Modules

A module is a Python file (.py) that contains functions, classes, and variables you can reuse in other files. Using modules helps you split large programs into smaller, focused files and avoid duplicated code.

Creating a Simple Module

Create support.py:

def print_func(name):
    print(f"Hello: {name}")

Keep module names simple (support.py, math_utils.py) and avoid hyphens/spaces in file names.

Import Statement

Use import to load a module:

# non-runnable: requires external environment/setup
import support

support.print_func("Andy")

import support keeps names scoped under support. and makes the origin of each function clearer.

Common Import Variants

# non-runnable: requires external environment/setup
from support import print_func
print_func("Bob")

import support as sp
sp.print_func("Carol")

Use from module import name when you only need a few symbols. Avoid wildcard imports (from x import *) because they make code harder to read and debug.

Module Search Path

When you run import module_name, Python searches in:

1. Current script directory
2. PYTHONPATH entries
3. Standard library and site-packages

You can inspect current paths:

import sys
print(sys.path)

If you see ModuleNotFoundError, run the script from your project root and verify the module file is in one of these paths.

__name__ == "__main__"

A module can behave differently when executed directly vs imported:

def main():
    print("Run as script")

if __name__ == "__main__":
    main()

• Run directly: python support.py -> main() runs
• Import from another file: main() does not run automatically

Packages

A package groups related modules inside a directory.

Example structure:

project/
  app.py
  helpers/
    __init__.py
    math_utils.py

Use:

# non-runnable: requires external environment/setup
from helpers.math_utils import add

__init__.py marks the folder as a package and helps tools resolve imports consistently.

Inspecting Module Members

Use dir() to inspect names exported by a module:

import math
print(dir(math))

Common Errors

• ModuleNotFoundError: wrong working directory or module path.
• ImportError: circular import or symbol not exported.
• Name conflict: your file has the same name as a standard/third-party module (for example random.py).