How to import custom module in Python

Python is a high-level programming language that supports various programming paradigms. It has a large ecosystem of libraries and third-party packages to support various functionalities. We can import modules to include external libraries and modules in our program and use their functionalities.

What is a custom module?

A custom module is a facility provided by Python to create a Python file containing reusable functions and classes that can be imported and used in different code files. It provides a more readable code interface and consequently improves maintainability.

Import validate.py in main.py to access its functions.
Import validate.py in main.py to access its functions.

Simple steps to import custom module

  1. Create a Python file for the module we need to import. Keep a relevant name and define all the required functionalities in it. For example, a validate.py file that contains validation functions.

def validate_num(num):
    if len(num) == 11:
        return True
def validate_pass(password):
    if len(password) < 7:
        return False

  1. Create a Python file for the program where the created module will be imported and used. For example, a main.py file that checks for the validity of a number and a password.

#need to import custom module here
print("Let's check for validity :\n")
number = '03001234567'
#need to add code here
paasword = 'key123'
#need to add code here

  1. Import the created module to the code file and use its functionalities according to the requirement. We can import the whole module or a single function from the module.

Import the whole custom module

The whole module is imported to the main.py file, which means that we can access all the functions and classes available inside the module and use them in our code. We can access the functions inside the module using the dot operator i.e. moduleName.functionName to specify from where the function is accessed.

Syntax

We can import the custom module by using the import keyword and specifying the module's name.

import validate

Example code

In this example, we import the validate module and use its validate_num() and validate_pass() functions to check the validities in our code.

main.py
validate.py
#import the whole custom module
import validate
print("Let's check for validity :\n")
number = '03001234567'
#access the function insdie the imported module
if validate.validate_num(number):
    print('num is valid')
else:
    print('num is invalid')
password = 'key123'
#access the function insdie the imported module
if validate.validate_pass(password):
    print('password is valid')
else:
    print('password is invalid')

Import a function from a custom module

A specific function is imported from the whole module to the main.py file, which means that we can access the specified function in our code. We can import more than one function from a single module i.e. import function1 , function2 , function3 when there is a specified need for functions.

Syntax

We can import a function from the custom module by using the from keyword to specify the destination module of the function and import keyword followed by the function's name.

from validate import validate_num

Example code

In this example, we import the validate_num() function from the validate module and use it to check the validity of numbers in our code.

main.py
validate.py
#import function from a custom module
from validate import validate_num
print("Let's check for validity :\n")
number = '03001234567'
#use the imported function
if validate_num(number):
    print('number is valid')
else:
    print('number is invalid')

Summary

Custom modules improve reusability and code accessibility by allowing users to store necessary functions in one place and use them according to their requirements. If the module is large and needs specified functions only, it is preferred to import functions. However, importing the whole module also works equally well.

Common query

Question

Why must we access a function using the dot operator if the whole module is already imported?

Show Answer

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