Python Modules

As our program grows bigger, it may contain many lines of code. Instead of putting everything in a single file, we can use modules to separate codes in separate files as per their functionality. This makes our code organized and easier to maintain.

Module is a file that contains code to perform a specific task. A module may contain variables, functions, classes etc. Let's see an example,

Let us create a module. Type the following and save it as example.py.

# Python Module addition

def add(a, b):

   result = a + b
   return result

Here, we have defined a function add() inside a module named example. The function takes in two numbers and returns their sum.

Import modules in Python

We can import the definitions inside a module to another module or the interactive interpreter in Python.

We use the import keyword to do this. To import our previously defined module example, we type the following in the Python prompt.

import example

This does not import the names of the functions defined in example directly in the current symbol table. It only imports the module name example there.

Using the module name we can access the function using the dot . operator. For example:

example.add(4,5) # returns 9

Import Python Standard Library Modules

The Python standard library contains well over 200 modules. We can import a module according to our needs.

Suppose we want to get the value of pi, first we import the math module and use math.pi. For example,

# import standard math module 
import math

# use math.pi to get value of pi
print("The value of pi is", math.pi)

Output

The value of pi is 3.141592653589793

Python import with Renaming

In Python, we can also import a module by renaming it. For example,

# import module by renaming it
import math as m

print(m.pi)

# Output: 3.141592653589793

Here, We have renamed the math module as m. This can save us typing time in some cases.

Note that the name math is not recognized in our scope. Hence, math.pi is invalid, and m.pi is the correct implementation.

Python from...import statement

We can import specific names from a module without importing the module as a whole. For example,

# import only pi from math module
from math import pi

print(pi)

# Output: 3.141592653589793

Here, we imported only the pi attribute from the math module.

Import all names

In Python, we can import all names(definitions) from a module using the following construct:

# import all names from the standard module math
from math import *

print("The value of pi is", pi)

Here, we have imported all the definitions from the math module. This includes all names visible in our scope except those beginning with an underscore(private definitions).

Importing everything with the asterisk (*) symbol is not a good programming practice. This can lead to duplicate definitions for an identifier. It also hampers the readability of our code.

The dir() built-in function

In Python, we can use the dir() function to list all the function names in a module.

For example, earlier we have defined a function add() in the module example.

We can use dir in example module in the following way:

print(dir(example))

['__builtins__',
'__cached__',
'__doc__',
'__file__',
'__initializing__',
'__loader__',
'__name__',
'__package__',
'add']

Here, we can see a sorted list of names (along with add). All other names that begin with an underscore are default Python attributes associated with the module (not user-defined).

For example, the __name__ attribute contains the name of the module.

import example

example.__name__

# Output: 'example'

All the names defined in our current namespace can be found out using the dir() function without any arguments.

a = 1
b = "hello"

import math

print(dir())

['__builtins__', '__doc__', '__name__', 'a', 'b', 'math', 'pyscripter']