Editing Subtyping (section)

===Python===
The following python code establishes an explicit inheritance relationship between classes {{var|B}} and {{var|A}}, where {{var|B}} is both a subclass and a subtype of {{var|A}}, and can be used as an {{var|A}} wherever a {{var|B}} is required.

<syntaxhighlight lang="python">
class A:
    def do_something_a_like(self):
        pass

class B(A):
    def do_something_b_like(self):
        pass

def use_an_a(some_a):
    some_a.do_something_a_like()

def some_func():
    b = B()
    use_an_a(b)  # b can be substituted for an A.
</syntaxhighlight>

The following example, {{var|type(a)}} is a "regular" type, and {{var|type(type(a))}} is a metatype. While as distributed all types have the same metatype ({{var|PyType_Type}}, which is also its own metatype), this is not a requirement. The type of classic classes, known as {{var|types.ClassType}}, can also be considered a distinct metatype.<ref>{{cite web|author=Guido van Rossum|title=Subtyping Built-in Types|url=https://www.python.org/dev/peps/pep-0253/|access-date=2 October 2012}}</ref>

<syntaxhighlight lang="pycon">
>>> a = 0
>>> type(a)
<type 'int'>
>>> type(type(a))
<type 'type'>
>>> type(type(type(a)))
<type 'type'>
>>> type(type(type(type(a))))
<type 'type'>
</syntaxhighlight>