What are Python namespaces all about

Question

I have just started learning Python & have come across "namespaces" concept in Python. While I got the jist of what it is, but am unable to appreciate the gravity of this concept.

Some browsing on the net revealed that one of the reasons going against PHP is that it has no native support for namespaces.

Could someone explain how to use namespaces & how this feature makes programming better (not just in Python, as I assume namespaces in not a concept limited to a particular language).

I am predominantly coming from JAVA and C programming backgrounds.

Answer 1

To understand namespaces, you also have to have some understanding of modules in Python. A module is simply a file containing Python code. This code can be in the form of Python classes, functions, or just a list of names. Each module gets it’s own global namespaces. So you can’t have two classes or two functions in the same module with the same name as they share the namespace of the module.

reference: http://bytebaker.com/2008/07/30/python-namespaces/

Answer 2

Namespaces prevent conflicts between classes, methods and objects with the same name that might have been written by different people.

Coming from a Java background you are probably familiar with how this is achieved using packages e.g. you might create a movieyoda.DateUtils class and I can create a mikej.DateUtils class and the package allows code using the classes to distinguish between them. (Python has something very similar.)

Namespaces were added to PHP in 5.3.0 but in earlier versions (and in other languages that don't provide namespaces) you would have to prefix your class and method names with something to reduce the risk of a name clash. e.g. a movieyoda_parse_file function.

Answer 3

Hi,

If you make a big program with someone else, you could write your own part of the program as you want. All variables in the file will be private, there will be no collisions. When you write PHP programs, it is easy to rewrite global variables by mistake. In python you can import other modules variables if you want, and they will be "global" on your module.

You could think one file one object in Python. When you write PHP programs you can achieve the same by writing classes with instance variables.

Answer 4

Namespace is a way to implement scope.

In Java (or C) the compiler determines where a variable is visible through static scope analysis.

• In C, scope is either the body of a function or it's global or it's external. The compiler reasons this out for you and resolves each variable name based on scope rules. External names are resolved by the linker after all the modules are compiled.

• In Java, scope is the body of a method function, or all the methods of a class. Some class names have a module-level scope, also. Again, the compiler figures this out at compile time and resolves each name based on the scope rules.

In Python, each package, module, class, function and method function owns a "namespace" in which variable names are resolved. Plus there's a global namespace that's used if the name isn't in the local namespace.

Each variable name is checked in the local namespace (the body of the function, the module, etc.), and then checked in the global namespace.

Variables are generally created only in a local namespace. The global and nonlocal statements can create variables in other than the local namespace.

When a function, method function, module or package is evaluated (that is, starts execution) a namespace is created. Think of it as an "evaluation context". When a function or method function, etc., finishes execution, the namespace is dropped. The variables are dropped. The objects may be dropped, also.