What are Libraries?

Imagine you need to find the square root of a number. You could write the math yourself — but that would take a while. Instead, Python lets you use a library: a collection of pre-written code that you can plug into your program.

Libraries save you from reinventing the wheel. Someone already wrote the hard part — you just import it.

Importing a Library

To use a library, add an import statement at the top of your file:

import math
 
print(math.sqrt(25))  # 5.0

The import math line loads the library. After that, you access its functions using a dot: math.sqrt(), math.floor(), etc.

Importing Specific Things

Sometimes you only need one function from a library. You can import just that piece:

from random import randint
 
print(randint(1, 10))

This lets you call randint() directly instead of random.randint().

Two Types of Libraries

Standard libraries come built into Python — no installation needed. There are over 200 of them. Examples: math, random, csv.

External libraries are written by the Python community and need to be installed before you can use them. Examples: Pillow (image editing), pandas (data analysis).