While learning python programming language we generally write some code or sample applications. But these will generally consist of a few lines of code below 100 lines. In real-world applications the situation is different. We generally write a lot of code, function, helpers, etc. Generally, these applications consist of above 10.000 lines of code. Putting all of these code into single or few py files are not a practical or logical solution. Python provides modules to make things more modular and tidy. We can put codes into different files in a hierarchical manner.

Create a Module

Creating a module is as easy as creating a source file and putting some code into this source file. We will create a module named mymodule.py with some code like below.

#Sum up given variables 
def sum(a,b): 
   return a+b

Module Search Path

We have created a module and put /home/ismail directory in operating system files system. But how can we access this module from different directories for load operation? Python uses a search path to locate modules named PYTHONPATH . Python follows below step to search and load modules

• Look current working directory
• Look PYTHONPATH environment variable provided directories
• Installation dependent default

Set PYTHONPATH

As previously stated we can provide a module directory different way. The most reliable way to set modules path is setting PYTHONPATH environment variable. We will run this command in the operating system shell. If we want to make PYTHONPATH variable persistent we should add this to startup-config.

This will add /home/ismail/modules to the PYTHONPATH in Linux systems.

$ PYTHONPATH=PYTHONPATH:/home/ismail/modules

Import Python Module

We have previously created a module named mymodule.py . We want to use the sum function inside this module. So we should import this module. We will import the module with import directive by specifying the module name with .py extension.

import mymodule

This will import module but if we want to call the function sum we should use the following line which provides module name specifier.

mymodule.sum(2,3)

This may be a bit trivial to specifying module names in every function or similar usage. We can commit the module name by importing like below. We will use from keyword and import all elements of the given module.

from mymodule import * 
sum(2,3)

Here we can call without providing a module name. We can implement this solutions mode multi-level modules too like below.

from mymodule.math import *

Get Name of Module

We have imported the module by using the source file name by removing the extension. We can get the module name in the application or interactive shell by calling __name__ global variable.

mymodule.__name__

List Module Functions, Attributes

Modules provide different variables, functions, sub-modules, attributes. We can list a module content with dir function. The result will the list of names provided by the module.

dir(math)