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How Imports Work

When your Python file needs code from another file or library, you use import.

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Visualize It

See how Python searches for and loads modules when you import: Open in Python Tutor

Basic import

import math
print(math.sqrt(16))    # 4.0

Import specific things

from math import sqrt, pi
print(sqrt(16))          # 4.0 — no "math." prefix needed
print(pi)                # 3.14159...

Import your own files

If you have two files in the same folder:

my_project/
├── main.py
└── helpers.py

# helpers.py
def greet(name):
    return f"Hello, {name}!"

# main.py
from helpers import greet
print(greet("Alice"))

Packages — folders of modules

A package is a folder that contains Python files and an __init__.py:

my_package/
├── __init__.py      # Makes this folder a package (can be empty)
├── calculator.py    # A module
└── statistics.py    # Another module

from my_package.calculator import add
from my_package import statistics

What __init__.py does

__init__.py runs when you import the package. It controls what gets exported:

# my_package/__init__.py
from my_package.calculator import add, subtract
from my_package.statistics import mean

# Now users can do:
# from my_package import add, mean

Without __init__.py, Python does not recognize the folder as a package.

The import search path

When you write import something, Python looks in this order:

  1. Current directory (the folder your script is in)
  2. Installed packages (site-packages/ — things you installed with pip)
  3. Standard library (modules that come with Python, like os, json, math)

You can see the full search path:

import sys
print(sys.path)

Common patterns

Alias (rename on import):

import pandas as pd
import numpy as np

Import everything (avoid this):

from math import *    # Bad — pollutes your namespace, hard to track what came from where

Conditional import:

try:
    import ujson as json    # Faster JSON library
except ImportError:
    import json             # Fall back to standard library

Common mistakes

Circular imports:

# file_a.py
from file_b import helper_b    # file_b imports from file_a → circular!

# file_b.py
from file_a import helper_a    # Fails with ImportError

Fix: restructure so both files import from a third file, or move imports inside functions.

Naming conflicts:

# Don't name your file "random.py" — it shadows the built-in random module!
import random    # Imports YOUR random.py instead of Python's

Missing __init__.py:

# If my_package/ has no __init__.py:
from my_package import calculator    # May fail in some Python versions

Practice

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