**Video link:**

In this video, we learned why modules are used and how we can import them in our program.

We then learned to create custom modules with the help of examples.

**Programs in the Video**

- [Python Modules](#python-modules-1)

- [Renaming modules](#renaming-modules)

- [Python from...import statement](#python-fromimport-statement)

- [The `dir()` function](#the-dir-function)

- [Custom Modules](#custom-modules)

A module is a file that contains Python code that we can use in our program.

There are several built-in functions like `print()`, `input()` and `sum()` that are readily available to us.

In addition to these functions, Python also has several functions that are defined inside a module which we can use after we import them.

Let's use one such module called `math`:

import math

number = 25

result = math.sqrt(number)

print(result)

print(math.pi)

**Output**

Once we import a module, we can use everything inside it using the dot operator.

We imported `math` using the `import` statement and called its `sqrt()` function that calculates the square root of a number.

Also, the value of the constant `pi` is printed to the screen.

While importing a module, we can also rename it to a different name as per our needs.

Let's rename the `math` module to `m`:

import math as m

number = 25

result = m.sqrt(number)

print(result)

print(m.pi)

**Output**

We get the same output as before.

When we import a module like in our previous examples, everything in the module is available to us.

However, if we only need to import a specific definition like a function or a constant, we can use the `from..import` statement.

from math import sqrt

num = sqrt(64)

print(num)

**Output**

Here, only the `sqrt` function is imported from the `math` module.

When we use this syntax, instead of `math.sqrt`, we need to directly use the `sqrt` function.

We can also import multiple definitions from the module in a single line using this syntax:

from math import pi, sin, sqrt

value = sin(pi/2)

print(value)

num = sqrt(64)

print(num)

**Output**

We can also use the `from...import` statement to import all definitions from a module using `*`:

from math import *

value = sin(pi/2)

print(value)

num = sqrt(64)

print(num)

**Output**

Here, asterisk `*` means import everything.

The `math` module comes with many more handy functions and constants.

We can list out all the things defined inside a module by using the `dir()` function:

import math

print(dir(math))

**Output**

As you can see, there are many other mathematical, trigonometric and logarithmic functions inside the `math` module.

In Python, we can also create our own custom modules as per our needs. This helps us to keep our code organized.

Let's a module named `calculator` that will contain functions to perform arithmetic operations.

First, create a file named `calculator.py` in the same directory and add the following:

def add(a, b):

return a + b

def subtract(a, b):

return a - b

def multiply(a, b):

return a * b

def divide(a, b):

return a / b

This file in itself is a module. Let's import this file from the main file.

In my main file:

import calculator

result1 = calculator.add(2, 3)

print(result1)

result2 = calculator.subtract(6, 3)

print(result2)

result3 = calculator.multiply(10, 3)

print(result3)

result4 = calculator.divide(6, 3)

print(result4)

**Output**

In our example, we have only used functions and constants from a module. However a module may also contain classes or any other definitions.

Now, we can already sense how useful a module is. It helps us in better code management and improves the reusability of our code.