(window.webpackJsonp=window.webpackJsonp||[]).push([[2713],{3124:function(t,s,a){"use strict";a.r(s);var n=a(31),e=Object(n.a)({},(function(){var t=this,s=t.$createElement,a=t._self._c||s;return a("ContentSlotsDistributor",{attrs:{"slot-key":t.$parent.slotKey}},[a("h1",{attrs:{id:"getting-started-with-python-language"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#getting-started-with-python-language"}},[t._v("#")]),t._v(" Getting started with Python Language")]),t._v(" "),a("h2",{attrs:{id:"getting-started"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#getting-started"}},[t._v("#")]),t._v(" Getting Started")]),t._v(" "),a("p",[t._v("Python is a widely used high-level programming language for general-purpose programming, created by Guido van Rossum and first released in 1991. Python features a dynamic type system and automatic memory management and supports multiple programming paradigms, including object-oriented, imperative, functional programming, and procedural styles. It has a large and comprehensive standard library.")]),t._v(" "),a("p",[t._v("Two major versions of Python are currently in active use:")]),t._v(" "),a("ul",[a("li",[t._v("Python 3.x is the current version and is under active development.")]),t._v(" "),a("li",[t._v("Python 2.x is the legacy version and will receive only security updates until 2020. No new features will be implemented. Note that many projects still use Python 2, although migrating to Python 3 is getting easier.")])]),t._v(" "),a("p",[t._v("You can download and install either version of Python "),a("a",{attrs:{href:"https://www.python.org/downloads/",target:"_blank",rel:"noopener noreferrer"}},[t._v("here"),a("OutboundLink")],1),t._v(". See "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/python/809/incompatibilities-moving-from-python-2-to-python-3#t=201703280213123640438",target:"_blank",rel:"noopener noreferrer"}},[t._v("Python 3 vs. Python 2"),a("OutboundLink")],1),t._v(" for a comparison between them. In addition, some third-parties offer re-packaged versions of Python that add commonly used libraries and other features to ease setup for common use cases, such as math, data analysis or scientific use. See "),a("a",{attrs:{href:"https://www.python.org/download/alternatives/",target:"_blank",rel:"noopener noreferrer"}},[t._v("the list at the official site"),a("OutboundLink")],1),t._v(".")]),t._v(" "),a("h3",{attrs:{id:"verify-if-python-is-installed"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#verify-if-python-is-installed"}},[t._v("#")]),t._v(" Verify if Python is installed")]),t._v(" "),a("p",[t._v("To confirm that Python was installed correctly, you can verify that by running the following command in your favorite terminal (If you are using Windows OS, you need to add path of python to the environment variable before using it in command prompt):")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("$ python "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("version\n\n")])])]),a("p",[t._v("If you have "),a("strong",[t._v("Python 3")]),t._v(" installed, and it is your default version (see "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/python/193/introduction-to-python/2653/idle-python-gui",target:"_blank",rel:"noopener noreferrer"}},[a("strong",[t._v("Troubleshooting")]),a("OutboundLink")],1),t._v(" for more details) you should see something like this:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("$ python "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("version\nPython "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("3.6")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v(".0")]),t._v("\n\n")])])]),a("p",[t._v("If you have "),a("strong",[t._v("Python 2")]),t._v(" installed, and it is your default version (see "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/python/193/introduction-to-python/2653/idle-python-gui",target:"_blank",rel:"noopener noreferrer"}},[a("strong",[t._v("Troubleshooting")]),a("OutboundLink")],1),t._v(" for more details) you should see something like this:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("$ python "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("version\nPython "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2.7")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v(".13")]),t._v("\n\n")])])]),a("p",[t._v("If you have installed Python 3, but "),a("code",[t._v("$ python --version")]),t._v(" outputs a Python 2 version, you also have Python 2 installed. This is often the case on MacOS, and many Linux distributions. Use "),a("code",[t._v("$ python3")]),t._v(" instead to explicitly use the Python 3 interpreter.")]),t._v(" "),a("h3",{attrs:{id:"hello-world-in-python-using-idle"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#hello-world-in-python-using-idle"}},[t._v("#")]),t._v(" Hello, World in Python using IDLE")]),t._v(" "),a("p",[a("a",{attrs:{href:"https://docs.python.org/2/library/idle.html",target:"_blank",rel:"noopener noreferrer"}},[t._v("IDLE"),a("OutboundLink")],1),t._v(" is a simple editor for Python, that comes bundled with Python.")]),t._v(" "),a("p",[a("strong",[t._v("How to create Hello, World program in IDLE")])]),t._v(" "),a("li",[t._v("Open IDLE on your system of choice.\n"),a("ul",[t._v("\n- In older versions of Windows, it can be found at `All Programs` under the Windows menu.\n- In Windows 8+, search for `IDLE` or find it in the apps that are present in your system.\n- On Unix-based (including Mac) systems you can open it from the shell by typing `$ idle python_file.py`.\n"),a("p",[t._v("In the shell, there is a prompt of three right angle brackets:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n\n")])])]),a("p",[t._v("Now write the following code in the prompt:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Hello, World"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("Hit "),a("kbd",[t._v("Enter")]),t._v(".")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Hello, World"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\nHello"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" World\n\n")])])]),a("h3",{attrs:{id:"hello-world-python-file"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#hello-world-python-file"}},[t._v("#")]),t._v(" Hello World Python file")]),t._v(" "),a("p",[t._v("Create a new file "),a("code",[t._v("hello.py")]),t._v(" that contains the following line:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Hello, World'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("You can use the Python 3 "),a("code",[t._v("print")]),t._v(" function in Python 2 with the following "),a("code",[t._v("import")]),t._v(" statement:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("from")]),t._v(" __future__ "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("import")]),t._v(" print_function\n\n")])])]),a("p",[t._v("Python 2 has a number of functionalities that can be optionally imported from Python 3 using the "),a("code",[t._v("__future__")]),t._v(" module, as "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/python/809/incompatibility-between-python-3-and-python-2/6894/use-future-imports#t=201612062212456247425",target:"_blank",rel:"noopener noreferrer"}},[t._v("discussed here"),a("OutboundLink")],1),t._v(".")]),t._v(" "),a("p",[t._v("If using Python 2, you may also type the line below. Note that this is not valid in Python 3 and thus not recommended because it reduces cross-version code compatibility.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Hello, World'")]),t._v("\n\n")])])]),a("p",[t._v("In your terminal, navigate to the directory containing the file "),a("code",[t._v("hello.py")]),t._v(".")]),t._v(" "),a("p",[t._v("Type "),a("code",[t._v("python hello.py")]),t._v(", then hit the "),a("kbd",[t._v("Enter")]),t._v(" key.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("$ python hello"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("py\nHello"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" World\n\n")])])]),a("p",[t._v("You should see "),a("code",[t._v("Hello, World")]),t._v(" printed to the console.")]),t._v(" "),a("p",[t._v("You can also substitute "),a("code",[t._v("hello.py")]),t._v(' with the path to your file. For example, if you have the file in your home directory and your user is "user" on Linux, you can type '),a("code",[t._v("python /home/user/hello.py")]),t._v(".")]),t._v(" "),a("h3",{attrs:{id:"launch-an-interactive-python-shell"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#launch-an-interactive-python-shell"}},[t._v("#")]),t._v(" Launch an interactive Python shell")]),t._v(" "),a("p",[t._v("By executing (running) the "),a("code",[t._v("python")]),t._v(" command in your terminal, you are presented with an interactive Python shell. This is also known as the "),a("a",{attrs:{href:"https://docs.python.org/3.6/tutorial/interpreter.html",target:"_blank",rel:"noopener noreferrer"}},[t._v("Python Interpreter"),a("OutboundLink")],1),t._v(" or  a REPL (for 'Read Evaluate Print Loop').")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("$ python\nPython "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2.7")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v(".12")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("default"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" Jun "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("28")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2016")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("08")]),a("span",{pre:!0,attrs:{class:"token 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"),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("$ python "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("i hello"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("py\n"),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Hello World"')]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n\n")])])]),a("p",[t._v("There are multiple ways to close the Python shell:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" exit"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token 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Code, compile, and run code in Python.")]),t._v(" "),a("li",[a("a",{attrs:{href:"https://www.tutorialspoint.com/execute_python_online.php",target:"_blank",rel:"noopener noreferrer"}},[t._v("https://www.tutorialspoint.com/execute_python_online.php"),a("OutboundLink")],1),t._v(" -\nFull-featured UNIX shell, and a user-friendly project explorer.")]),t._v(" "),a("li",[a("a",{attrs:{href:"http://rextester.com/l/python3_online_compiler",target:"_blank",rel:"noopener noreferrer"}},[t._v("http://rextester.com/l/python3_online_compiler"),a("OutboundLink")],1),t._v(" - Simple and easy to use IDE which\nshows execution time")])])])]),t._v(" "),a("h3",{attrs:{id:"run-commands-as-a-string"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#run-commands-as-a-string"}},[t._v("#")]),t._v(" Run commands as a string")]),t._v(" "),a("p",[t._v("Python can be passed arbitrary code as a string in the shell:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("$ python "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("c "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'print(\"Hello, World\")'")]),t._v("\nHello"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" World\n\n")])])]),a("p",[t._v("This can be useful when concatenating the results of scripts together in the shell.")]),t._v(" "),a("h3",{attrs:{id:"shells-and-beyond"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#shells-and-beyond"}},[t._v("#")]),t._v(" Shells and Beyond")]),t._v(" "),a("p",[a("strong",[t._v("Package Management")]),t._v(" - The PyPA recommended tool for installing Python packages is "),a("a",{attrs:{href:"https://pip.pypa.io/en/stable/",target:"_blank",rel:"noopener noreferrer"}},[t._v("PIP"),a("OutboundLink")],1),t._v(". To install, on your command line execute "),a("code",[t._v("pip install <the package name>")]),t._v(". For instance, "),a("code",[t._v("pip install numpy")]),t._v(". (Note: On windows you must add pip to your PATH environment variables. To avoid this, use "),a("code",[t._v("python -m pip install <the package name>")]),t._v(")")]),t._v(" "),a("p",[a("strong",[t._v("Shells")]),t._v(" - So far, we have discussed different ways to run code using Python's native interactive shell.  Shells use Python's interpretive power for experimenting with code real-time.  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Formatting code well is important so you can quickly read what the code does.")]),t._v(" "),a("h2",{attrs:{id:"creating-variables-and-assigning-values"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#creating-variables-and-assigning-values"}},[t._v("#")]),t._v(" Creating variables and assigning values")]),t._v(" "),a("p",[t._v("To create a variable in Python, all you need to do is specify the variable name, and then assign a value to it.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("variable name"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("value"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n\n")])])]),a("p",[t._v("Python uses "),a("code",[t._v("=")]),t._v(" to assign values to variables. There's no need to declare a variable in advance (or to assign a data type to it), assigning a value to a variable itself declares and initializes the variable with that value. There's no way to declare a variable without assigning it an initial value.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Integer")]),t._v("\na "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: 2")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Integer    ")]),t._v("\nb "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("9223372036854775807")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: 9223372036854775807")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Floating point")]),t._v("\npi "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("3.14")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("pi"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: 3.14")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# String")]),t._v("\nc "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'A'")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: A")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# String    ")]),t._v("\nname "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'John Doe'")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: John Doe")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Boolean    ")]),t._v("\nq "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("True")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("q"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: True")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Empty value or null data type")]),t._v("\nx "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("None")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: None")]),t._v("\n\n")])])]),a("p",[t._v("Variable assignment works from left to right. So the following will give you an syntax error.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" x\n"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" Output"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" SyntaxError"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" can't assign to literal\n\n")])])]),a("p",[t._v("You can not use python's keywords as a valid variable name. You can see the list of keyword by:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("import")]),t._v(" keyword\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("keyword"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("kwlist"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("Rules for variable naming:")]),t._v(" "),a("ol",[a("li",[t._v("Variables names must start with a letter or an underscore.")])]),t._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[t._v("\nx  = True   # valid\n _y = True   # valid\n\n 9x = False  # starts with numeral \n => SyntaxError: invalid syntax   \n\n $y = False #  starts with symbol \n => SyntaxError: invalid 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This dummy variable can have any name, but it is conventional to use the underscore ("),a("code",[t._v("_")]),t._v(") for assigning unwanted values:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" _ "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("3")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: 1, 2")]),t._v("\n\n")])])]),a("p",[t._v("Note that the number of _ and number of remaining values must be equal. Otherwise 'too many values to unpack error' is thrown as above:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" _ "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("4")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("Traceback "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("most recent call last"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("File "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"name.py"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" line N"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("in")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("module"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" _ "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("4")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("ValueError"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" too many values to unpack "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("expected "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("You can also assign a single value to several variables simultaneously.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" b "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" c "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: 1 1 1")]),t._v("\n\n")])])]),a("p",[t._v("When using such cascading assignment, it is important to note that all three variables "),a("code",[t._v("a")]),t._v(", "),a("code",[t._v("b")]),t._v(" and "),a("code",[t._v("c")]),t._v(" refer to the "),a("strong",[t._v("same object")]),t._v(" in memory, an "),a("code",[t._v("int")]),t._v(" object with the value of 1. 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Assigning a different object to one of them afterwards doesn't change the  others, just as expected:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" b "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" c "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),t._v("    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# all three names a, b and c refer to same int object with value 1")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: 1 1 1")]),t._v("\nb "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),t._v("            "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# b now refers to another int object, one with a value of 2")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: 1 2 1  # so output is as expected.")]),t._v("\n\n")])])]),a("p",[t._v("The above is also true for mutable types (like "),a("code",[t._v("list")]),t._v(", "),a("code",[t._v("dict")]),t._v(", etc.) just as it is true for immutable types (like "),a("code",[t._v("int")]),t._v(", "),a("code",[t._v("string")]),t._v(", "),a("code",[t._v("tuple")]),t._v(", etc.):")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" y "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("7")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("8")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("9")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v("   "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# x and y refer to the same list object just created, [7, 8, 9]")]),t._v("\nx "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("13")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("8")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("9")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v("      "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# x now refers to a different list object just created, [13, 8, 9]")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("y"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("            "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# y still refers to the list it was first assigned")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: [7, 8, 9]")]),t._v("\n\n")])])]),a("p",[t._v("So far so good. Things are a bit different when it comes to "),a("strong",[t._v("modifying")]),t._v(" the object (in contrast to "),a("strong",[t._v("assigning")]),t._v(" the name to a different object, which we did above) when the cascading assignment is used for mutable types. Take a look below, and you will see it first hand:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" y "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("7")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("8")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("9")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v("     "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# x and y are two different names for the same list object just created, [7, 8, 9]")]),t._v("\nx"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("13")]),t._v("             "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# we are updating the value of the list [7, 8, 9] through one of its names, x in this case")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("y"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("              "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# printing the value of the list using its other name")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: [13, 8, 9]  # hence, naturally the change is reflected")]),t._v("\n\n")])])]),a("p",[t._v("Nested lists are also valid in python. This means that a list can contain another list as an element.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("4")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("6")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("7")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# this is nested list")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: [3, 4, 5]")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: 4")]),t._v("\n\n")])])]),a("p",[t._v("Lastly, variables in Python do not have to stay the same type as which they were first defined -- you can simply use "),a("code",[t._v("=")]),t._v(" to assign a new value to a variable, even if that value is of a different type.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),t._v(" \n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: 2")]),t._v("\n\na "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"New value"')]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Output: New value")]),t._v("\n\n")])])]),a("p",[t._v("If this bothers you, think about the fact that what's on the left of "),a("code",[t._v("=")]),t._v(" is just a name for an object. First you call the "),a("code",[t._v("int")]),t._v(" object with value 2 "),a("code",[t._v("a")]),t._v(", then you change your mind and decide to give the name "),a("code",[t._v("a")]),t._v(" to a "),a("code",[t._v("string")]),t._v(" object, having value 'New value'. Simple, right?")]),t._v(" "),a("h2",{attrs:{id:"block-indentation"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#block-indentation"}},[t._v("#")]),t._v(" Block Indentation")]),t._v(" "),a("p",[t._v("Python uses indentation to define control and loop constructs. This contributes to Python's readability, however, it requires the programmer to pay close attention to the use of whitespace. Thus, editor miscalibration could result in code that behaves in unexpected ways.")]),t._v(" "),a("p",[t._v("Python uses the colon symbol ("),a("code",[t._v(":")]),t._v(") and indentation for showing where blocks of code begin and end (If you come from another language, do not confuse this with somehow being related to the "),a("a",{attrs:{href:"https://en.wikipedia.org/wiki/%3F:",target:"_blank",rel:"noopener noreferrer"}},[t._v("ternary operator"),a("OutboundLink")],1),t._v("). That is, blocks in Python, such as functions, loops, "),a("code",[t._v("if")]),t._v(" clauses and other constructs, have no ending identifiers. All blocks start with a colon and then contain the indented lines below it.")]),t._v(" "),a("p",[t._v("For example:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("def")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("my_function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# This is a function definition. Note the colon (:)")]),t._v("\n    a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),t._v("             "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# This line belongs to the function because it's indented")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" a          "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# This line also belongs to the same function")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("my_function"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# This line is OUTSIDE the function block")]),t._v("\n\n")])])]),a("p",[t._v("or")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("             "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# If block starts here")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("          "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# This is part of the if block")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("else")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("                 "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# else must be at the same level as if")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("          "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# This line is part of the else block")]),t._v("\n\n")])])]),a("p",[t._v("Blocks that contain exactly one single-line statement may be put on the same line, though this form is generally not considered good style:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("else")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("  \n\n")])])]),a("p",[t._v("Attempting to do this with more than a single statement will "),a("strong",[t._v("not")]),t._v(" work:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" y"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" y "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" x\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("y"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# IndentationError: unexpected indent")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" y"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("while")]),t._v(" y "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("!=")]),t._v(" z"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" y "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# SyntaxError: invalid syntax")]),t._v("\n\n")])])]),a("p",[t._v("An empty block causes an "),a("code",[t._v("IndentationError")]),t._v(". Use "),a("code",[t._v("pass")]),t._v(" (a command that does nothing) when you have a block with no content:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("def")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("will_be_implemented_later")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("pass")]),t._v("\n\n")])])]),a("h3",{attrs:{id:"spaces-vs-tabs"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#spaces-vs-tabs"}},[t._v("#")]),t._v(" Spaces vs. Tabs")]),t._v(" "),a("p",[t._v("In short: "),a("strong",[t._v("always")]),t._v(" use 4 spaces for indentation.")]),t._v(" "),a("p",[t._v("Using tabs exclusively is possible but "),a("a",{attrs:{href:"https://www.python.org/dev/peps/pep-0008/#tabs-or-spaces",target:"_blank",rel:"noopener noreferrer"}},[t._v("PEP 8"),a("OutboundLink")],1),t._v(", the style guide for Python code, states that spaces are preferred.")]),t._v(" "),a("p",[t._v("Python 3 disallows mixing the use of tabs and spaces for indentation. In such case a compile-time error is generated: "),a("code",[t._v("Inconsistent use of tabs and spaces in indentation")]),t._v(" and the program will not run.")]),t._v(" "),a("p",[t._v("Python 2 allows mixing tabs and spaces in indentation; this is strongly discouraged. The tab character completes the previous indentation to be a "),a("a",{attrs:{href:"https://docs.python.org/2/reference/lexical_analysis.html#indentation",target:"_blank",rel:"noopener noreferrer"}},[t._v("multiple of "),a("strong",[t._v("8")]),t._v(" spaces"),a("OutboundLink")],1),t._v(". 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When configuring the editor, one should differentiate between the tab '),a("strong",[t._v("character")]),t._v(" ('\\t') and the "),a("kbd",[t._v("Tab")]),t._v(" key.")]),t._v(" "),a("ul",[a("li",[t._v("The tab "),a("strong",[t._v("character")]),t._v(" should be configured to show 8 spaces, to match the language semantics - at least in cases when (accidental) mixed indentation is possible. 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Tuples can also be nested and the values can be any valid Python valid.")]),t._v(" "),a("p",[t._v("A tuple with only one member must be defined (note the comma) this way:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("one_member_tuple "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Only member'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("or")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("one_member_tuple "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Only member'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("   "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# No brackets")]),t._v("\n\n")])])]),a("p",[t._v("or just using "),a("code",[t._v("tuple")]),t._v(" syntax")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("one_member_tuple "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("tuple")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Only member'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[a("strong",[t._v("Dictionaries")])]),t._v(" "),a("p",[t._v("A "),a("code",[t._v("dictionary")]),t._v(" in Python is a collection of key-value pairs. The dictionary is surrounded by curly braces. Each pair is separated by a comma and the key and value are separated by a colon. Here is an example:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("state_capitals "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Arkansas'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Little Rock'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Colorado'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Denver'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'California'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Sacramento'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" \n    "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Georgia'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Atlanta'")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("To get a value, refer to it by its key:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("ca_capital "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" state_capitals"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'California'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v("\n\n")])])]),a("p",[t._v("You can also get all of the keys in a dictionary and then iterate over them:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("for")]),t._v(" k "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("in")]),t._v(" state_capitals"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("keys"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'{} is the capital of {}'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("format")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("state_capitals"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),t._v("k"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" k"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("Dictionaries strongly resemble JSON syntax. The native "),a("code",[t._v("json")]),t._v(" module in the Python standard library can be used to convert between JSON and dictionaries.")]),t._v(" "),a("p",[a("strong",[t._v("set")])]),t._v(" "),a("p",[t._v("A "),a("code",[t._v("set")]),t._v(" is a collection of elements with no repeats and without insertion order but sorted order. They are used in situations where it is only important that some things are grouped together, and not what order they were included.  For large groups of data, it is much faster to check whether or not an element is in a "),a("code",[t._v("set")]),t._v(" than it is to do the same for a "),a("code",[t._v("list")]),t._v(".")]),t._v(" "),a("p",[t._v("Defining a "),a("code",[t._v("set")]),t._v(" is very similar to defining a "),a("code",[t._v("dictionary")]),t._v(":")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("first_names "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Adam'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Beth'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Charlie'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("Or you can build a "),a("code",[t._v("set")]),t._v(" using an existing "),a("code",[t._v("list")]),t._v(":")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("my_list "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v("\nmy_set "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("set")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("my_list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("Check membership of the "),a("code",[t._v("set")]),t._v(" using "),a("code",[t._v("in")]),t._v(":")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" name "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("in")]),t._v(" first_names"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("You can iterate over a "),a("code",[t._v("set")]),t._v(" exactly like a list, but remember: the values will be in a arbitrary, implementation-defined order.")]),t._v(" "),a("p",[a("strong",[t._v("defaultdict")])]),t._v(" "),a("p",[t._v("A "),a("code",[t._v("defaultdict")]),t._v(" is a dictionary with a default value for keys, so that keys for which no value has been explicitly defined can be accessed without errors. "),a("code",[t._v("defaultdict")]),t._v(" is especially useful when the values in the dictionary are collections (lists, dicts, etc) in the sense that it does not need to be initialized every time when a new key is used.")]),t._v(" "),a("p",[t._v("A "),a("code",[t._v("defaultdict")]),t._v(" will never raise a KeyError. Any key that does not exist gets the default value returned.")]),t._v(" "),a("p",[t._v("For example, consider the following dictionary")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" state_capitals "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Arkansas'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Little Rock'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Colorado'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Denver'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'California'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Sacramento'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" \n    "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Georgia'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Atlanta'")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("If we try to access a non-existent key, python returns us an error as follows")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" state_capitals"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Alabama'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v("\nTraceback "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("most recent call last"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n\n  File "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"<ipython-input-61-236329695e6f>"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" line "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("in")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("module"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n    state_capitals"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Alabama'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v("\n\nKeyError"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Alabama'")]),t._v("\n\n")])])]),a("p",[t._v("Let us try with a "),a("code",[t._v("defaultdict")]),t._v(". It can be found in the collections module.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("from")]),t._v(" collections "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("import")]),t._v(" defaultdict\n"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" state_capitals "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" defaultdict"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("lambda")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Boston'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("What we did here is to set a default value ("),a("strong",[t._v("Boston")]),t._v(") in case the give key does not exist. Now populate the dict as before:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" state_capitals"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Arkansas'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Little Rock'")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" state_capitals"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'California'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Sacramento'")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" state_capitals"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Colorado'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Denver'")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" state_capitals"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Georgia'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Atlanta'")]),t._v("\n\n")])])]),a("p",[t._v("If we try to access the dict with a non-existent key, python will return us the default value i.e. Boston")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" state_capitals"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Alabama'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Boston'")]),t._v("\n\n")])])]),a("p",[t._v("and returns the created values for existing key just like a normal "),a("code",[t._v("dictionary")])]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" state_capitals"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Arkansas'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Little Rock'")]),t._v("\n\n")])])]),a("h2",{attrs:{id:"idle-python-gui"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#idle-python-gui"}},[t._v("#")]),t._v(" IDLE - Python GUI")]),t._v(" "),a("p",[t._v("IDLE is Python’s Integrated Development and Learning Environment and is an alternative to the command line. As the name may imply, IDLE is very useful for developing new code or learning python. On Windows this comes with the Python interpreter, but in other operating systems you may need to install it through your package manager.")]),t._v(" "),a("p",[t._v("The main purposes of IDLE are:")]),t._v(" "),a("ul",[a("li",[t._v("Multi-window text editor with syntax highlighting, autocompletion, and smart indent")]),t._v(" "),a("li",[t._v("Python shell with syntax highlighting\n")]),a("li",[t._v("Integrated debugger with stepping, persistent breakpoints, and call\nstack visibility")]),t._v(" "),a("li",[t._v("Automatic indentation (useful for beginners learning about Python's indentation)")]),t._v(" "),a("li",[t._v("Saving the Python program as .py files and run them and edit them later at any them using IDLE.")])]),t._v(" "),a("p",[t._v("In IDLE, hit "),a("code",[t._v("F5")]),t._v(" or "),a("code",[t._v("run Python Shell")]),t._v(" to launch an interpreter. Using IDLE can be a better learning experience for new users because code is interpreted as the user writes.")]),t._v(" "),a("p",[t._v("Note that there are lots of alternatives, see for example "),a("a",{attrs:{href:"http://stackoverflow.com/questions/81584/what-ide-to-use-for-python",target:"_blank",rel:"noopener noreferrer"}},[t._v("this discussion"),a("OutboundLink")],1),t._v(" or "),a("a",{attrs:{href:"https://wiki.python.org/moin/PythonEditors",target:"_blank",rel:"noopener noreferrer"}},[t._v("this list"),a("OutboundLink")],1),t._v(".")]),t._v(" "),a("h3",{attrs:{id:"troubleshooting"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#troubleshooting"}},[t._v("#")]),t._v(" Troubleshooting")]),t._v(" "),a("li",[t._v("\n**Windows**\nIf you're on Windows, the default command is `python`. If you receive a `\"'python' is not recognized\"` error, the most likely cause is that Python's location is not in your system's `PATH` environment variable. This can be accessed by right-clicking on 'My Computer' and selecting 'Properties' or by navigating to 'System' through 'Control Panel'. Click on 'Advanced system settings' and then 'Environment Variables...'. Edit the `PATH` variable to include the directory of your Python installation, as well as the Script folder (usually `C:\\Python27;C:\\Python27\\Scripts`). This requires administrative privileges and may require a restart.\nWhen using multiple versions of Python on the same machine, a possible solution is to rename one of the `python.exe` files. For example, naming one version `python27.exe` would cause `python27` to become the Python command for that version.\nYou can also use the Python Launcher for Windows, which is available through the installer and comes by default. It allows you to select the version of Python to run by using `py -[x.y]` instead of `python[x.y]`. You can use the latest version of Python 2 by running scripts with `py -2` and the latest version of Python 3 by running scripts with `py -3`.\n")]),t._v(" "),a("li",[t._v("\n**Debian/Ubuntu/MacOS**\nThis section assumes that the location of the `python` executable has been added to the `PATH` environment variable.\nIf you're on Debian/Ubuntu/MacOS, open the terminal and type `python` for Python 2.x or `python3` for Python 3.x.\nType `which python` to see which Python interpreter will be used.\n")]),t._v(" "),a("li",[t._v("\n**Arch Linux**\nThe default Python on Arch Linux (and descendants) is Python 3, so use `python` or `python3` for Python 3.x and `python2` for Python 2.x.\n")]),t._v(" "),a("li",[t._v("\n**Other systems**\nPython 3 is sometimes bound to `python` instead of `python3`. To use Python 2 on these systems where it is installed, you can use `python2`.\n")]),t._v(" "),a("h2",{attrs:{id:"user-input"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#user-input"}},[t._v("#")]),t._v(" User Input")]),t._v(" "),a("p",[a("strong",[t._v("Interactive input")])]),t._v(" "),a("p",[t._v("To get input from the user, use the "),a("code",[t._v("input")]),t._v(" function ("),a("strong",[t._v("note")]),t._v(": in Python 2.x, the function is called "),a("code",[t._v("raw_input")]),t._v(" instead, although Python 2.x has its own version of "),a("a",{attrs:{href:"https://docs.python.org/2/library/functions.html#input",target:"_blank",rel:"noopener noreferrer"}},[a("code",[t._v("input")]),a("OutboundLink")],1),t._v(" that is completely different):")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("raw_input")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"What is your name? "')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Out: What is your name? _")]),t._v("\n\n")])])]),a("blockquote"),t._v(" "),a("p",[a("strong",[t._v("Security Remark")]),t._v(" Do not use "),a("code",[t._v("input()")]),t._v(" in Python2 - the entered text will be evaluated as if it were a Python expression (equivalent to "),a("code",[t._v("eval(input())")]),t._v(" in Python3), which might easily become a vulnerability. See "),a("a",{attrs:{href:"https://medium.com/@GallegoDor/python-exploitation-1-input-ac10d3f4491f#.cr6w4z7q8",target:"_blank",rel:"noopener noreferrer"}},[t._v("this article"),a("OutboundLink")],1),t._v(" for further information on the risks of using this function.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("input")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"What is your name? "')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Out: What is your name? _")]),t._v("\n\n")])])]),a("p",[t._v("The remainder of this example will be using Python 3 syntax.")]),t._v(" "),a("p",[t._v("The function takes a string argument, which displays it as a prompt and returns a string. The above code provides a prompt, waiting for the user to input.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("input")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"What is your name? "')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Out: What is your name?")]),t._v("\n\n")])])]),a("p",[t._v('If the user types "Bob" and hits enter, the variable '),a("code",[t._v("name")]),t._v(" will be assigned to the string "),a("code",[t._v('"Bob"')]),t._v(":")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("input")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"What is your name? "')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Out: What is your name? Bob")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Out: Bob")]),t._v("\n\n")])])]),a("p",[t._v("Note that the "),a("code",[t._v("input")]),t._v(" is always of type "),a("code",[t._v("str")]),t._v(", which is important if you want the user to enter numbers. Therefore, you need to convert the "),a("code",[t._v("str")]),t._v(" before trying to use it as a number:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("input")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Write a number:"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Out: Write a number: 10")]),t._v("\nx "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Out: TypeError: unsupported operand type(s) for /: 'str' and 'int'")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("float")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Out: 5.0")]),t._v("\n\n")])])]),a("p",[t._v("NB: It's recommended to use "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/python/1788/exceptions/5530/catching-exceptions#t=201607241956183569764",target:"_blank",rel:"noopener noreferrer"}},[a("code",[t._v("try")]),t._v("/"),a("code",[t._v("except")]),t._v(" blocks"),a("OutboundLink")],1),t._v(" to "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/python/1788/exceptions/8484/practical-examples-of-exception-handling#t=201607241956183569764",target:"_blank",rel:"noopener noreferrer"}},[t._v("catch exceptions when dealing with user inputs"),a("OutboundLink")],1),t._v(". For instance, if your code wants to cast a "),a("code",[t._v("raw_input")]),t._v(" into an "),a("code",[t._v("int")]),t._v(", and what the user writes is uncastable, it raises a "),a("code",[t._v("ValueError")]),t._v(".")]),t._v(" "),a("h2",{attrs:{id:"built-in-modules-and-functions"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#built-in-modules-and-functions"}},[t._v("#")]),t._v(" Built in Modules and Functions")]),t._v(" "),a("p",[t._v("A module is a file containing Python definitions and statements. Function is a piece of code which execute some logic.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">>")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("pow")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("#8")]),t._v("\n\n")])])]),a("p",[t._v("To check the built in function in python we can use "),a("code",[t._v("dir().")]),t._v(" If called without an argument, return the names in the current scope. 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