Question

The following Python code executes normally without raising an exception:

class Foo:
    pass

class Foo:
    pass

def bar():
    pass

def bar():
    pass

print(Foo.__module__ + Foo.__name__)

Yet clearly, there are multiple instances of __main__.Foo and __main__.bar. Why does Python not raise an error when it encounters this namespace collision? And since it doesn’t raise an error, what exactly is it doing? Is the first class __main__.Foo replaced by the second class __main__.Foo?

Answer 1

In Python everything is an object – instance of some type. E.g. 1 is an instance of type int, def foo(): pass creates object foo which is an instance of type function (same for classes – objects, created by class statement are instances of type type). Given this, there no difference (at the level of name binding mechanism) between

class Foo:
  string = "foo1"

class Foo:
  string = "foo2"

and

a = 1
a = 2

BTW, class definition may be performed using type function (yeah, there is type type and built-in function type):

Foo = type('Foo', (), {string: 'foo1'})

So classes and functions are not some different kind of data, although special syntax may be used for creating their instances.

See also related Data Model section.