Python Modules: import, from ... import, and Creating Your Own

A module is simply a Python file that contains code (functions, variables, classes) you can reuse in other files. Python ships with hundreds of ready-made modules, called the standard library, and you can write your own to keep large programs organised.

Importing a module#

import math

print(math.sqrt(16), math.pi, math.ceil(4.2), math.floor(4.8))

4.0 3.141592653589793 5 4

import math loads the module once; you then use its contents with dot notation: math.sqrt, math.pi.

Importing specific names#

from ... import ... brings names directly into your file, so you can drop the prefix:

from math import sqrt, pi

print(sqrt(25), round(pi, 3))

5.0 3.142

You can also give a module a shorter alias:

import datetime as dt
print(type(dt.date(2026, 10, 23)).__name__)

date

A tour of useful standard modules#

import random

random.seed(42)   # makes the "random" results repeatable
print(random.randint(1, 6), random.choice(["red", "green", "blue"]))

nums = [1, 2, 3, 4, 5]
random.shuffle(nums)
print(nums)

6 red
[2, 4, 5, 3, 1]

Without random.seed(42), you would get different values each run, which is usually what you want. Seeding is useful for tests and for reproducing results.

import statistics

data = [70, 85, 85, 90, 100]
print(statistics.mean(data), statistics.median(data), statistics.mode(data))

86 85 85

Other modules you will use often:

To see what a module contains, use dir() or help():

import math
print(dir(math)[:8])

['__doc__', '__loader__', '__name__', '__package__', '__spec__', 'acos', 'acosh', 'asin']

Creating your own module#

Any .py file is a module. Create helpers.py:

"""Small helper functions."""

TAX_RATE = 0.18

def add_tax(price):
    return round(price * (1 + TAX_RATE), 2)

def greet(name):
    return f"Hello, {name}!"

In another file in the same folder:

import helpers

print(helpers.add_tax(100))
print(helpers.greet("Asha"))
print(helpers.TAX_RATE)

from helpers import greet
print(greet("Ravi"))

118.0
Hello, Asha!
0.18
Hello, Ravi!

The module name is the file name without .py.

if name == "main"#

When Python runs a file directly, it sets the special variable __name__ to "__main__". When the file is imported, __name__ is the module's name instead. This lets a file contain code that runs only when executed directly:

def double(n):
    return n * 2

if __name__ == "__main__":
    print("Running tools.py directly")
    print(double(21))

Running python tools.py prints both lines. But importing it from another file:

import tools
print("imported, double(5) =", tools.double(5))

imported, double(5) = 10

The test code inside the if did not run. This pattern lets a module be both a reusable library and a runnable script.

When an import fails#

import nonexistent_module

ModuleNotFoundError: No module named 'nonexistent_module'

Usual causes:

1. A typo in the name.
2. A third-party package that is not installed yet: install it with python -m pip install name (see Packages).
3. Your own module is in a different folder from the file importing it.
4. You named your own file the same as a module, such as random.py, which hides the real one.

Common mistakes#

Practice#

import math

r = 7
print(round(math.pi * r ** 2, 2))
print(math.ceil(r / 2))

153.94
4

Key takeaway#