Modules and imports

A module is just a Python file. import lets one file use the functions and values defined in another — including the vast standard library that ships with Python. This is the project-shape and abstraction ideas in practice: organise code into files, and use them through their public names.

Importing

The standard library is full of ready-made tools. Import a module and use its contents with a dot:

import math
math.sqrt(16)       # 4.0
math.pi             # 3.14159...

import vs from-import vs alias

Three forms, each useful:

import random                 # use as random.choice(...)
from random import choice     # bring one name in directly: choice(...)
import statistics as stats    # alias a long name: stats.mean(...)

from x import y is handy when you use one or two things a lot; plain import x keeps the source visible (random.choice says where choice came from), which aids readability.

Your own files are modules too

If you have helpers.py with a function greet, another file imports it by filename:

# in main.py, next to helpers.py
from helpers import greet
greet("Ada")

This is how projects grow beyond one file — each module owns a focused job (cohesion), and others use it through its names (its interface).

Where to go next

That completes Python Core syntax. The intermediate Idioms & structure module goes Pythonic: comprehensions, generators, decorators, classes, and type hints.