What are Python namespaces?

Why are they used in python?

A simple way to put it is that when you are writing a 100,000-lines program, it is impossible to choose different names for all variables. So, every function defines a namespace. It is like a box with bindings (variables) inside, and the variables cannot be accessed from the outside.

>>> def f(x):
...     a = x + 2
...     print(a)
>>> f(5)
>>> a
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'a' is not defined

Modules are also namespaces. There is not a single sqrt function for example. The one from math applies to floats. The one from cmath also handles complex number. Thanks to namespaces, there is no conflict between these functions. They are called math.sqrt and so on.

Furthermore, you will discover when you learn object-oriented programming that objects are namespaces too. A simple example is file objects:

>>> file = open("foo")
>>> file.name
>>> file.closed
>>> file.mode
>>> file.encoding

See? This file object has associated data, which it owns. The object is a form of namespace.

You can read a lot on the net about namespaces, like