Learning Python

Module Files Are Namespaces

Modules are probably best understood as places to define names you want visible to the rest of a system. In Python-speak, modules are a namespace—a place where names are created. And names that live in a module are called its attributes. Technically, modules correspond to files, and Python creates a module object to contain all the names defined in the file; but in simple terms, modules are just namespaces.

So how do files become namespaces? Every name that is assigned a value at the top level of a module file (i.e., not in a function body) becomes an attribute of that module. For instance, given an assignment statement such as X=1 at the top level of a module file M.py, the name X becomes an attribute of M, which we can refer to from outside the module as M.X. The name X also becomes a global variable to other code inside M.py, but we need to explain the notion of module loading and scopes a bit more formally to understand why:

Module statements run on the first import

The first time a module is imported anywhere in a system, Python creates an empty module object and executes the statements in the module file one after another, from the top of the file to the bottom.

Top-level assignments create module attributes

During an import, statements at the top-level of the file that assign names (e.g., =, def) create attributes of the module object; assigned names are stored in the module’s namespace.

Module namespace: attribute _ _dict__, or dir( )

Module namespaces ...