{"id":1652,"date":"2019-12-27T14:04:18","date_gmt":"2019-12-27T14:04:18","guid":{"rendered":"https:\/\/www.askpython.com\/?p=1652"},"modified":"2019-12-27T14:04:21","modified_gmt":"2019-12-27T14:04:21","slug":"metaclass-in-python","status":"publish","type":"post","link":"https:\/\/www.askpython.com\/python\/metaclass-in-python","title":{"rendered":"Metaclass in Python"},"content":{"rendered":"\n

A Metaclass<\/em><\/strong> is the class of a class. Whenever an instance of a class (object) is created, the way that the object behaves is defined by the Class. A Metaclass defines the behavior of the Class itself.<\/p>\n\n\n\n

\n\n\n\n

Use of Metaclass in Python<\/h2>\n\n\n\n

The reason behind the use of Metaclasses is that Python Classes are Objects themselves. Since Classes are Objects, we can do various operations on it, such as assigning it to a variable, copying, etc.<\/p>\n\n\n\n

And since they are objects, we can create them dynamically, as we can do for any other object.<\/p>\n\n\n\n

\n\n\n\n

To understand the concept of Metaclasses better, we first look at how Python defines Classes. The language defines everything as an object, whether it be an int<\/code>, a string<\/code>, or anything else.<\/p>\n\n\n\n

To look at the type of any Python object, if you remember, we use the type<\/code> function.<\/p>\n\n\n

\n>>> print(type(123))\n<class 'int'>\n>>> print(type([1, 2, 3]))\n<class 'list'>\n\n>>> class A():\n...     def __init__(self):\n...             pass\n...\n>>> a = A()\n>>> print(type(a))\n<class '__main__.A'>\n<\/pre><\/div>\n\n\n
It returns a class<\/code> for each case, as we can observe. But to see how Python defines the class itself, we simply look at its type.<\/p>\n\n\n
\n>>> print(type(type(123))\n<class 'type'>\n>>> print(type(A))\n<class 'type'>\n<\/pre><\/div>\n\n\n
As you can see, the type(class<\/code>) is the class type<\/code>! So it turns out that the class is defined by a class itself? What is this phenomenon?<\/p>\n\n\n\n
This is the concept of a metaclass, which serves to define other classes. Basically, it is a class factory, from which other classes such as int<\/code>s and str<\/code>s can be defined. <\/p>\n\n\n\n
\"Metaclass\"
Metaclass hierarchy<\/figcaption><\/figure>\n\n\n\n
type<\/code> is the metaclass which the language uses to create an<\/em> object. (which is why every object has a type)<\/p>\n\n\n\n
And because type<\/code> is a metaclass, we can create other classes from it.<\/p>\n\n\n\n
\n\n\n\n
Creating Classes Dynamically<\/h2>\n\n\n\n
We can create classes dynamically by instantiation from the type constructor: type(name, bases, attr)<\/code><\/p>\n\n\n\n