Python Modules

What is a Module?

Consider a module to be the same as a code library.

A file containing a set of functions you want to include in your application.

Create a Module

To create a module just save the code you want in a file with the file extension .py:

Example

Save this code in a file named mymodule.py

def greeting(name):
print("Hello, " + name)

Use a Module

Now we can use the module we just created, by using the import statement:

Example

Import the module named mymodule, and call the greeting function:

import mymodule

mymodule.greeting("Jonathan")

Note: When using a function from a module, use the syntax: module_name.function_name.

Variables in Module

The module can contain functions, as already described, but also variables of all types (arrays, dictionaries, objects etc):

Example

Save this code in the file mymodule.py

person1 = {
"name": "John",
"age": 36,
"country": "Norway"
}

Example

Import the module named mymodule, and access the person1 dictionary:

import mymodule

a = mymodule.person1["age"]
print(a)

Naming a Module

You can name the module file whatever you like, but it must have the file extension .py

Re-naming a Module

You can create an alias when you import a module, by using the as keyword:

Example

Create an alias for mymodule called mx:

import mymodule as mx

a = mx.person1["age"]
print(a)

Built-in Modules

There are several built-in modules in Python, which you can import whenever you like.

Example

Import and use the platform module:

import platform

x = platform.system()
print(x)

Using the dir() Function

There is a built-in function to list all the function names (or variable names) in a module. The dir() function:

Example

List all the defined names belonging to the platform module:

import platform

x = dir(platform)
print(x)

Note: The dir() function can be used on all modules, also the ones you create yourself.

Import From Module

You can choose to import only parts from a module, by using the from keyword.

Example

The module named mymodule has one function and one dictionary:

def greeting(name):
print("Hello, " + name)

person1 = {
"name": "John",
"age": 36,
"country": "Norway"
}

Example

Import only the person1 dictionary from the module:

from mymodule import person1

print (person1["age"])

Note: When importing using the from keyword, do not use the module name when referring to elements in the module. Example: person1["age"], not mymodule.person1["age"]

Where to Store a Module?

You can store the modules in the same directory as the rest of your python files, or you can choose a different location.

Python will start by searching the current directory, then it will search in every location described in the PYTHONPATH variable.

To see which locations that are described in the PYTHONPATH variable, check the sys.path property:

Example

List all the locations described in the PYTHONPATH property:

import sys

print(sys.path)

To add locations to the PYTHONPATH variable use the set PYTHONPATH statement:

Example

Add a new location to the PYTHONPATH property:

C:\Users\Your Name>set PYTHONPATH = C:\Users\Your Name\python_modules

Note: The dir() function can be used on all modules.