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.

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
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# 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
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# Importing only specific functions from a module
from math import sqrt, floor

# 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
89
y = floor(3.7)
print(f"Floor of 3.7 is {y}")
Floor of 3.7 is 3

Importing with renaming

Python 3.13
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# 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

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
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# 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
789101112
# 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
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# 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
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# 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 next lesson we'll look at built-in libraries — the ones available right after you install Python.