Using Libraries in Python

Libraries are sets of ready-made code that you can use in your programs. They allow you to avoid "reinventing the wheel" and achieve results faster by using solutions created by other developers.

What are libraries?

A library (or module) in Python is a file with code containing functions, classes, and variables that you can use in your programs.

Libraries help:

Save time by avoiding writing code "from scratch"
Use proven, optimized solutions
Extend the capabilities of the Python language
Create more complex programs with less effort

Importing libraries

To use a library, you first need to import it into your program. Python offers several ways to import:

Importing the entire library

Python 3.13
# Importing the entire math library
>>> import math

# Using functions through the library name
>>> radius = 5
>>> circle_area = math.pi * radius ** 2
>>> print(f"The area of a circle with radius {radius} is {circle_area:.2f}")
The area of a circle with radius 5 is 78.54

Importing specific elements

Python 3.13
# Importing only specific functions from a module
>>> from math import sqrt, pow

# Using imported functions directly
>>> x = 16
>>> result = sqrt(x)
>>> print(f"The square root of {x} is {result}")
The square root of 16 is 4.0

>>> y = pow(2, 3)
>>> print(f"2 to the power of 3 is {y}")
2 to the power of 3 is 8.0

Importing with renaming

Python 3.13
# Importing a module with an alternative name (alias)
>>> import math as m

>>> angle = 45
# Using m instead of math
>>> sin_value = m.sin(m.radians(angle))
>>> print(f"The sine of {angle} degrees is {sin_value:.4f}")
The sine of 45 degrees is 0.7071

Importing all elements

Python 3.13
# Importing all elements from a module
# Note: this method is generally not recommended
>>> from math import *

>>> radius = 3
# Using pi and cos directly, without specifying math
>>> print(f"π is approximately {pi:.5f}")
>>> print(f"The cosine of 0 is {cos(0)}")
π is approximately 3.14159
The cosine of 0 is 1.0

Types of libraries in Python

In Python, there are three main types of libraries:

Built-in modules — modules that are already included in the Python standard library and are available immediately after installing Python.
Third-party libraries — modules created by other developers that need to be installed additionally.
Custom modules — modules that you create yourself to organize your code.

Examples of built-in modules

Python 3.13
# The random module for generating random numbers
>>> import random

# Generating a random number from 1 to 10
>>> random_number = random.randint(1, 10)
>>> print(f"Random number: {random_number}")
Random number: 7

# The datetime module for working with dates and times
>>> import datetime

# Getting the current date and time
>>> current_date = datetime.datetime.now()
>>> print(f"Current date and time: {current_date}")
Current date and time: 2023-07-15 14:30:45.123456

Finding functions in the documentation

When working with libraries, it's important to know how to find information about available functions. Python provides several ways:

Using the help() function

Python 3.13
# Getting information about a module
>>> import math
>>> help(math)  # Will only display the beginning of the help to avoid overloading the example
Help on module math:

NAME
    math

MODULE REFERENCE
    https://docs.python.org/3.12/library/math.html

    The following documentation is automatically generated from the Python
    source files.  It may be incomplete, incorrect or include features that
    are considered implementation detail and may vary between Python
    implementations.  When in doubt, consult the module reference at the
    location listed above.

DESCRIPTION
    This module provides access to the mathematical functions
    defined by the C standard.

FUNCTIONS
    acos(x, /)
        Return the arc cosine (measured in radians) of x.

        The result is between 0 and pi.
...

Using the dir() function

Python 3.13
# Getting a list of all available attributes and methods
>>> import random
>>> attributes = dir(random)

# Let's display only the first 10 elements for brevity
>>> print(attributes[:10])
['BPF', 'LOG4', 'NV_MAGICCONST', 'RECIP_BPF', 'Random', 'SG_MAGICCONST', 'SystemRandom', 'TWOPI', '_ONE', '_Sequence']

Understanding Check

Let's check how well you've understood the topic of libraries:

Which of the following library import methods are correct in Python?

In the following lessons, we will look at specific libraries and their applications in more detail.