Python Foundation - part three

Metaclasses in Python3

>>> class FooBar:
pass
>>> type(FooBar)
<class 'type'>
>>> f = FooBar()
>>> type(f)
<class '__main__.FooBar'>

>>> isinstance(foo, Foobar)
True
>>> isinstance(Foobar, type)
True

These examples mean instance is an instance of a class, a class is an instance of metaclass. and

type

is very useful metaclass in python as we have seen.

we can use

type

to create a class like this:

>>> MyClass = type('MyClass', (), {})
>>> MyClass
<class '__main__.MyClass'>

As type is a metaclass, so we can also create a custom metaclass that extens type

>>> class Meta(type):
...     pass

Difference between , _ and xx in Python

One underscore in the beginning

one underscore marks a private method or attribute

Two underscores in the beginning

Such methods with two underscores can not be overrided.

Two underscores in the beginning and in the end

Such methods are called magic methods which only python can call. Some useful methods are

__call__

__new__

__init__

__prepare__

These four methods are very important for instance and class creation.