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README.md

Basics Python

Topics

Argument Parser

  • The argparse module will “parse” the “arguments” to the program.
    • Make the name optional by changing the name of the argument to --name
    • -n for the “short” and and --name for “long” option names.
    • metavar value of “name” to describe what the value should be.
import argparse

parser = argparse.ArgumentParser(description='Say hello')
# parser.add_argument('name', help='user_name to greet') # positional argument 'name'
parser.add_argument('-n', '--name', metavar='user_name',
                    default='World', help='user_name to greet')
args = parser.parse_args()

print('Hello, ' + args.name + '!')

# use vars() to make args as the dict
args = vars(parser.parse_args())
print('Hello, ' + args['name'] + '!')
Type Example Required Default
Positional name Yes No
Optinal -n (short), --name (long)) No Yes
  • -h and --help to get the documentation
optional arguments:
  -h, --help                      show this help message and exit
  -n user_name, --name user_name  user_name to greet

Code Formater

  • The PEP 8 (Python Enhancement Proposal) describes best practices for formatting code, and most IDEs and text editors will have tools to help you format your code so that it’s easier to read and find problems.

Code Linter

  • A code linter is a tool that will report problems in your code, such as declaring a variable but never using it.
  • Two most popular code linter: Pylint and Flake8, and both can find errors in your code that the Python interpreter itself will not complain about.
  • Mypy can use to find problems along with type hints, such as using text when you should be using a number.

Makefile

  • If there is something you need to do literally hundreds of times, say run pytest, so you can creat a Makefile that looks like this:
.PHONY: test

test:
    pytest -xv test.py
  • If you have the program make installed on your computer, you can run you can run make test to execute pytest -xv test.py
    • The make program will look for a Makefile in your current working directory and then look for a recipe called “test.”

Pip

  • Show package information: pip show -f <pkgname>
  • Upgrade package: pip install --upgrade <pkgname>
  • Uninstall & install again: pip install --ignore-installed <pkgname>

Python IDLE

  • Python can run into 2 modes: Interactive (Python IDLE, IPython) & Script mode
  • The IDLE application (REPL because it’s a Read-Evaluate-Print-Loop) allows you to interact directly with the Python language. Each statement you type is evaluated when you press Enter, and the results are shown in the window.
  • The IPython program is yet another “interactive Python” REPL that has many enhancements over IDLE and python3

Shebang #!

  • Python programs live in plain text files
  • It’s common to put a special comment line in programs like #!/usr/bin/env python3 these to indicate which language needs to be used to execute the commands in the file.
  • Python will ignore the shebang, but the operating systems (like macOS or Windows) will use it to decide which program to use to run the rest of the file.
  • Below is the shebang you should add at the beginning of the file
#!/usr/bin/env python3
  • The shebang line tells the operating system to use the env program (located at /usr/bin/env) to find the python3 that is specific to the machine on which it’s running.

Executable Python Program

  • So far we’ve been explicitly telling python3 to run our program (python3 hello.py), but since we added the shebang, we can execute the program directly and let the OS figure out that it should use python3.
  • The first step in doing this is to make our program “executable” using the command chmod
chmod +x hello.py # +x will add an “executable” attribute to the file

# Now can run the program like
# The . / is the current directory, and it’s necessary to run a program when you are in the same directory as the program.
./hello.py