A module in Python is a file (ending in .py) that contains a set of definitions (variables and functions) that you can use when they are imported. Modules are considered as objects, just as everything else is in Python. Many methods can operate on modules. As mentioned previously, the dir() function can list all the objects imported and available to work with in your active Python session. The name of the module that contains all the built-in Python functions is called __builtins__ and can be accessed:

dir(__builtins__)

Another example of a method that can operate on modules is the str() function, returning a string representation of the module including the pathname on your local disk. Outside of the __builtins__ module, there are many modules in Python that you can import to access familiar functions.

Importing modules

There are two ways to import modules. The first is to use the word import followed by the name of the module:

import math

This will import a module named math which containing functions such as log(), sin(), cos(), etc. To access this functions, you have to specify the name of the module and the name of the function separated by a dot (or period): e.g. math.sin(x). To access the value of $\pi$, use math.pi

The second way to import a module is with the words from and import. This allows you to use the name of the functions directly without having to type the name of the module and a period in front of the name of the function. To import a specific function from the math module, use the first line. To import everything from a module, use the second line.

from math import pi
from math import *

Now you can use pi directly. To see all the variables and functions available in the math module, use dir().

dir(math)

Going back to the __builtins__ modules, you can think of Python automatically importing this module on the startup of your Python session:

from __builtins__ import *

Reloading modules

When you import a module in python, all the variables and functions are stored in a namespace. The next time you use import, the existing module will be loaded. If the module has been changed, to force a reload, use reload()

import mymodule
reload(mymodule)

Module attributes

Every Python class has a built-in class attribute __module__ which is the name of the module in which the class is defined. For example, the following will tell us the function sin() came from the math module.

sin.__module__

Writing modules

Any file that contains Python code and ends in .py can be imported as a module. If your file name is cool.py, you can import the program directly

import cool
print cool

which will print that the object ‘cool’ is a module from ‘cool.py’. The functions inside the module are accessed in same syntax as before: the name of the module, a dot (or period) and the name of the function.

Note: If you import a module that has already been imported, Python will not re-read the file (even if it has changed!). To reload the module, use the built-in Python function reload.

Other useful modules

copy

• copy.copy() = function to duplicate any object (not create an alias)

types

This module can be used to compare the types of any object.

import types
type(os) == types.ModuleType