Post History

A namespace is a category to which a name can belong. Think of family names for people: I may be friends with several Jims, and if only one of them is present I can just call him Jim. But if multiple are present, I can disambiguate which I mean by saying Jim Jones or Jim Smith. ‘Jones’ and ‘Smith’ are namespaces which can both contain the name ‘Jim’, and thanks to them the name ‘Jim’ can be used by two different people without ambiguity.

In programming languages, sometimes types, variables, functions, labels (thing you can `goto`), struct fields, etc. all belong to distinct namespaces—if I write `foo(a, b);`, a compiler or interpreter might know to look for `foo` in the function namespace and ignore any variables or types that are also named `foo`. Python doesn't do this; variables and functions (and types, when using type annotations) are all looked up in the same namespace.

Programming languages also often have a concept of a ‘module’ or a ‘package’, which is another way to create namespaces. Python does have these, of course; I can define a function `foo` in module `wibble`, and you can define a function `foo` in module `babble`, and a user can disambiguate them by importing the modules and writing `wibble.foo` or `babble.foo`.

This is not an exhaustive classification; other types of namespaces are possible, but these are two of the most common.

A namespace may or may not have a run-time representation. Python modules do, but the term/type/etc. namespaces in languages like C and Haskell don't, nor do the module-like namespaces in Java and C#. As an abstract concept, the only important quality of a namespace is the ability to use the same name to mean different things in different contexts without ambiguity.