(window.webpackJsonp=window.webpackJsonp||[]).push([[2664],{3074: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:"classes"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#classes"}},[t._v("#")]),t._v(" Classes")]),t._v(" "),a("p",[t._v("Python offers itself not only as a popular scripting language, but also supports the object-oriented programming paradigm. Classes describe data and provide methods to manipulate that data, all encompassed under a single object. Furthermore, classes allow for abstraction by separating concrete implementation details from abstract representations of data.")]),t._v(" "),a("p",[t._v("Code utilizing classes is generally easier to read, understand, and maintain.")]),t._v(" "),a("h2",{attrs:{id:"introduction-to-classes"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#introduction-to-classes"}},[t._v("#")]),t._v(" Introduction to classes")]),t._v(" "),a("p",[t._v("A class, functions as a template that defines the basic characteristics of a particular object. Here's an 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("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Person")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("object")]),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 triple-quoted-string string"}},[t._v('"""A simple class."""')]),t._v("                            "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# docstring")]),t._v("\n     species "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Homo Sapiens"')]),t._v("                         "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# class attribute")]),t._v("\n\n     "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("def")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("__init__")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" name"),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("# special method")]),t._v("\n         "),a("span",{pre:!0,attrs:{class:"token triple-quoted-string string"}},[t._v('"""This is the initializer. It\'s a special\n         method (see below).\n         """')]),t._v("\n         self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" name                             "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# instance attribute")]),t._v("\n\n     "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("def")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("__str__")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("self"),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("# special method")]),t._v("\n         "),a("span",{pre:!0,attrs:{class:"token triple-quoted-string string"}},[t._v('"""This method is run when Python tries \n         to cast the object to a string. Return \n         this string when using print(), etc.\n         """')]),t._v("\n         "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("name\n\n     "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("def")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("rename")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" renamed"),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("# regular method")]),t._v("\n         "),a("span",{pre:!0,attrs:{class:"token triple-quoted-string string"}},[t._v('"""Reassign and print the name attribute."""')]),t._v("\n         self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" renamed\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('"Now my name is {}"')]),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("self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("name"),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("There are a few things to note when looking at the above example.")]),t._v(" "),a("ol",[a("li",[t._v("The class is made up of "),a("strong",[t._v("attributes")]),t._v(" (data) and "),a("strong",[t._v("methods")]),t._v(" (functions).")]),t._v(" "),a("li",[t._v("Attributes and methods are simply defined as normal variables and functions.")]),t._v(" "),a("li",[t._v("As noted in the corresponding docstring, the "),a("code",[t._v("__init__()")]),t._v(" method is called the "),a("strong",[t._v("initializer")]),t._v(". It's equivalent to the constructor in other object oriented languages, and is the method that is first run when you create a new object, or new instance of the class.")]),t._v(" "),a("li",[t._v("Attributes that apply to the whole class are defined first, and are called "),a("strong",[t._v("class attributes")]),t._v(".")]),t._v(" "),a("li",[t._v("Attributes that apply to a specific instance of a class (an object) are called "),a("strong",[t._v("instance attributes")]),t._v(". They are generally defined inside "),a("code",[t._v("__init__()")]),t._v("; this is not necessary, but it is recommended (since attributes defined outside of "),a("code",[t._v("__init__()")]),t._v(" run the risk of being accessed before they are defined).")]),t._v(" "),a("li",[t._v("Every method, included in the class definition passes the object in question as its first parameter. The word "),a("code",[t._v("self")]),t._v(" is used for this parameter (usage of "),a("code",[t._v("self")]),t._v(" is actually by convention, as the word "),a("code",[t._v("self")]),t._v(" has no inherent meaning in Python, but this is one of Python's most respected conventions, and you should always follow it).")]),t._v(" "),a("li",[t._v("Those used to object-oriented programming in other languages may be surprised by a few things. One is that Python has no real concept of "),a("code",[t._v("private")]),t._v(" elements, so everything, by default, imitates the behavior of the C++/Java "),a("code",[t._v("public")]),t._v(' keyword. For more information, see the "Private Class Members" example on this page.')]),t._v(" "),a("li",[t._v("Some of the class's methods have the following form: "),a("code",[t._v("__functionname__(self, other_stuff)")]),t._v('. All such methods are called "magic methods" and are an important part of classes in Python. For instance, operator overloading in Python is implemented with magic methods. For more information, see '),a("a",{attrs:{href:"http://stackoverflow.com/documentation/python/2063/overloading/1113/magic-dunder-methods#t=201608092225343955327",target:"_blank",rel:"noopener noreferrer"}},[t._v("the relevant documentation"),a("OutboundLink")],1),t._v(".")])]),t._v(" "),a("p",[t._v("Now let's make a few instances of our "),a("code",[t._v("Person")]),t._v(" class!")]),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 comment"}},[t._v("# Instances")]),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(" kelly "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" Person"),a("span",{pre:!0,attrs:{class:"token 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operator"}},[t._v(">")]),t._v(" john_doe"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("__str__"),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 string"}},[t._v("'John Doe'")]),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("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("john_doe"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'John Doe'")]),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("  john_doe"),a("span",{pre:!0,attrs:{class:"token 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In Python 3 when you declare a method within a class, you are using a "),a("code",[t._v("def")]),t._v(" keyword, thus creating a function object. This is a regular function, and the surrounding class works as its namespace. In the following example we declare method "),a("code",[t._v("f")]),t._v(" within class "),a("code",[t._v("A")]),t._v(", and it becomes a function "),a("code",[t._v("A.f")]),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("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("object")]),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("def")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("f")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" x"),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("return")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v(" x\nA"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("f\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# <function A.f at ...>  (in Python 3.x)")]),t._v("\n\n")])])]),a("p",[t._v("In Python 2 the behavior was different: function objects within the class were implicitly replaced with objects of type "),a("code",[t._v("instancemethod")]),t._v(", which were called "),a("strong",[t._v("unbound methods")]),t._v(" because they were not bound to any particular class instance. It was possible to access the underlying function using "),a("code",[t._v(".__func__")]),t._v(" property.")]),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("f\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# <unbound method A.f>   (in Python 2.x)")]),t._v("\nA"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("f"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("__class__\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# <type 'instancemethod'>")]),t._v("\nA"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("f"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("__func__\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# <function f at ...>")]),t._v("\n\n")])])]),a("p",[t._v("The latter behaviors are confirmed by inspection - methods are recognized as functions in Python 3, while the distinction is upheld in Python 2.")]),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(" inspect\n\ninspect"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("isfunction"),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("f"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# True")]),t._v("\ninspect"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("ismethod"),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("f"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# False")]),t._v("\n\n")])])]),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(" inspect\n\ninspect"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("isfunction"),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("f"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# False")]),t._v("\ninspect"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("ismethod"),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("f"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# True")]),t._v("\n\n")])])]),a("p",[t._v("In both versions of Python function/method "),a("code",[t._v("A.f")]),t._v(" can be called directly, provided that you pass an instance of class "),a("code",[t._v("A")]),t._v(" as the first argument.")]),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("f"),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("7")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Python 2: TypeError: unbound method f() must be called with")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("#                      A instance as first argument (got int instance instead) ")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Python 3: 14   ")]),t._v("\na "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" A"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\nA"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("f"),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 number"}},[t._v("20")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Python 2 & 3: 40")]),t._v("\n\n")])])]),a("p",[t._v("Now suppose "),a("code",[t._v("a")]),t._v(" is an instance of class "),a("code",[t._v("A")]),t._v(", what is "),a("code",[t._v("a.f")]),t._v(" then? Well, intuitively this should be the same method "),a("code",[t._v("f")]),t._v(" of class "),a("code",[t._v("A")]),t._v(', only it should somehow "know" that it was applied to the object '),a("code",[t._v("a")]),t._v(" – in Python this is called method "),a("strong",[t._v("bound")]),t._v(" to "),a("code",[t._v("a")]),t._v(".")]),t._v(" "),a("p",[t._v("The nitty-gritty details are as follows: writing "),a("code",[t._v("a.f")]),t._v(" invokes the magic "),a("code",[t._v("__getattribute__")]),t._v(" method of "),a("code",[t._v("a")]),t._v(", which first checks whether "),a("code",[t._v("a")]),t._v(" has an attribute named "),a("code",[t._v("f")]),t._v(" (it doesn't), then checks the class "),a("code",[t._v("A")]),t._v(" whether it contains a method with such a name (it does), and creates a new object "),a("code",[t._v("m")]),t._v(" of type "),a("code",[t._v("method")]),t._v(" which has the reference to the original "),a("code",[t._v("A.f")]),t._v(" in "),a("code",[t._v("m.__func__")]),t._v(", and a reference to the object "),a("code",[t._v("a")]),t._v(" in "),a("code",[t._v("m.__self__")]),t._v(". When this object is called as a function, it simply does the following: "),a("code",[t._v("m(...) => m.__func__(m.__self__, ...)")]),t._v(". Thus this object is called a "),a("strong",[t._v("bound method")]),t._v(" because when invoked it knows to supply the object it was bound to as the first argument. (These things work same way in Python 2 and 3).")]),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"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\na"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("f\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# <bound method A.f of <__main__.A object at ...>>")]),t._v("\na"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("f"),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("# 4")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Note: the bound method object a.f is recreated *every time* you call it:")]),t._v("\na"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("f "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("is")]),t._v(" a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("f  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# False")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# As a performance optimization you can store the bound method in the object's")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# __dict__, in which case the method object will remain fixed:")]),t._v("\na"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("f "),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("f\na"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("f "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("is")]),t._v(" a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("f  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# True")]),t._v("\n\n")])])]),a("p",[t._v("Finally, Python has "),a("strong",[t._v("class methods")]),t._v(" and "),a("strong",[t._v("static methods")]),t._v(" – special kinds of methods. Class methods work the same way as regular methods, except that when invoked on an object they bind to the "),a("strong",[t._v("class")]),t._v(" of the object instead of to the object. Thus "),a("code",[t._v("m.__self__ = type(a)")]),t._v(". When you call such bound method, it passes the class of "),a("code",[t._v("a")]),t._v(" as the first argument. Static methods are even simpler: they don't bind anything at all, and simply return the underlying function without any transformations.")]),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("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("D")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("object")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n    multiplier "),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\n    "),a("span",{pre:!0,attrs:{class:"token decorator annotation punctuation"}},[t._v("@classmethod")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token 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For more details on classmethods and staticmethods:")]),t._v(" "),a("ul",[a("li",[a("a",{attrs:{href:"http://stackoverflow.com/questions/136097/what-is-the-difference-between-staticmethod-and-classmethod-in-python",target:"_blank",rel:"noopener noreferrer"}},[t._v("What is the difference between @staticmethod and @classmethod in Python?"),a("OutboundLink")],1)]),t._v(" "),a("li",[a("a",{attrs:{href:"http://stackoverflow.com/questions/12179271/python-classmethod-and-staticmethod-for-beginner",target:"_blank",rel:"noopener noreferrer"}},[t._v("Meaning of @classmethod and @staticmethod for beginner?"),a("OutboundLink")],1)])]),t._v(" "),a("h2",{attrs:{id:"basic-inheritance"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#basic-inheritance"}},[t._v("#")]),t._v(" Basic inheritance")]),t._v(" "),a("p",[t._v("Inheritance in Python is based on similar ideas used in other object oriented languages like Java, C++ etc.\nA new class can be derived from an existing class 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 keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("BaseClass")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("object")]),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("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("DerivedClass")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("BaseClass"),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("p",[t._v("The "),a("code",[t._v("BaseClass")]),t._v(" is the already existing ("),a("strong",[t._v("parent")]),t._v(") class, and the "),a("code",[t._v("DerivedClass")]),t._v(" is the new ("),a("strong",[t._v("child")]),t._v(") class that inherits (or "),a("strong",[t._v("subclasses")]),t._v(") attributes from "),a("code",[t._v("BaseClass")]),t._v(".  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"),a("strong",[t._v("A new-style class is a user-defined type")]),t._v(", and is very similar to built-in types.")]),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("# new-style class")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("New")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("object")]),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("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# new-style instance")]),t._v("\nnew "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" New"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\nnew"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("__class__\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# <class '__main__.New'>")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("type")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("new"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# <class '__main__.New'>")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("issubclass")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("New"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("object")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# True")]),t._v("\n\n")])])]),a("p",[a("strong",[t._v("Old-style")]),t._v(" classes do "),a("strong",[t._v("not")]),t._v(" inherit from "),a("code",[t._v("object")]),t._v(". Old-style instances are always implemented with a built-in "),a("code",[t._v("instance")]),t._v(" type.")]),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("# old-style class")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Old")]),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("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# old-style instance")]),t._v("\nold "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" Old"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\nold"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("__class__\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# <class __main__.Old at ...>")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("type")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("old"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# <type 'instance'>")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("issubclass")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("Old"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("object")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# False")]),t._v("\n\n")])])]),a("p",[t._v("In Python 3, old-style classes were removed.")]),t._v(" "),a("p",[t._v("New-style classes in Python 3 implicitly inherit from "),a("code",[t._v("object")]),t._v(", so there is no need to specify "),a("code",[t._v("MyClass(object)")]),t._v(" anymore.")]),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("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("MyClass")]),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\nmy_inst "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" MyClass"),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("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("type")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("my_inst"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# <class '__main__.MyClass'>")]),t._v("\nmy_inst"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("__class__\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# <class '__main__.MyClass'>")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("issubclass")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("MyClass"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("object")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# True")]),t._v("\n\n")])])]),a("h2",{attrs:{id:"class-methods-alternate-initializers"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#class-methods-alternate-initializers"}},[t._v("#")]),t._v(" Class methods: alternate initializers")]),t._v(" "),a("p",[t._v("Class methods present alternate ways to build instances of classes. To illustrate, let's look at an example.")]),t._v(" "),a("p",[t._v("Let's suppose we have a relatively simple "),a("code",[t._v("Person")]),t._v(" class:")]),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("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Person")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("object")]),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("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("def")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("__init__")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" first_name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" last_name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" age"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n        self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("first_name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" first_name\n        self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("last_name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" last_name\n        self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("age "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" age\n        self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("full_name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" first_name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('" "')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" last_name\n    \n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("def")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("greet")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("self"),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('"Hello, my name is "')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("full_name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"."')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("It might be handy to have a way to build instances of this class specifying a full name instead of first and last name separately. One way to do this would be to have "),a("code",[t._v("last_name")]),t._v(" be an optional parameter, and assuming that if it isn't given, we passed the full name in:")]),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("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Person")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("object")]),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("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("def")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("__init__")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" first_name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" age"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" last_name"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("None")]),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("if")]),t._v(" last_name "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("is")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("None")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n            self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("first_name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("last_name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" first_name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("split"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('" "')]),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("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("else")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n            self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("first_name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" first_name\n            self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("last_name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" last_name\n        \n        self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("full_name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("first_name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('" "')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("last_name\n        self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("age "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" age\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("def")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("greet")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("self"),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('"Hello, my name is "')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" self"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("full_name "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"."')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("However, there are two main problems with this bit of code:")]),t._v(" "),a("li",[t._v("\nThe parameters `first_name` and `last_name` are now misleading, since you can enter a full name for `first_name`. Also, if there are more cases and/or more parameters that have this kind of flexibility, the if/elif/else branching can get annoying fast.\n")]),t._v(" "),a("li",[t._v("\nNot quite as important, but still worth pointing out: what if `last_name` is `None`, but `first_name` doesn't split into two or more things via spaces? We have yet another layer of input validation and/or exception handling...\n")]),t._v(" "),a("p",[t._v("Enter class methods. Rather than having a single initializer, we will create a separate initializer, called "),a("code",[t._v("from_full_name")]),t._v(", and decorate it with the (built-in) "),a("code",[t._v("classmethod")]),t._v(" decorator.")]),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("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Person")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("object")]),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("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("def")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("__init__")]),a("span",{pre:!0,attrs:{class:"token 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