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How to Import and Use Functions from Another Python File

How to Import and Use Functions from Another Python File

How to Import and Use Functions from Another Python File

Splitting your Python code into multiple files is a core skill for organizing larger projects and promoting code reuse. Python’s import statement lets you access functions and variables defined in another file (called a "module") to keep your code clean, maintainable, and modular. This guide covers how imports work, common patterns, and practical examples to help you use them like a pro.

Table of Content

Why Import Functions from Another File?

  • Reusability: Write functions once and use them in many programs.
  • Organization: Keep related functions together by topic.
  • Maintainability: Fix bugs or update code in just one place.
  • Collaboration: Work as a team with well-separated code files.

Syntax & Structure

# Import an entire module (file)
import module_name

# Import specific function(s) from a module
from module_name import function_name

# Import with alias
import module_name as mn
from module_name import function_name as fn

# Import multiple functions
from module_name import func1, func2
  • module_name: The name of the file without .py (e.g., my_utils.py → my_utils).
  • function_name: The function you want to use from the module.
  • as: Gives an imported name an alias for convenience.

Basic Import Examples

For all these examples, assume you have a file math_utils.py: 
def add(a, b):
    return a + b

def square(x):
    return x * x

1. Import the Whole Module

import math_utils

result = math_utils.add(2, 3)
print(result)

Output

5

2. Import a Specific Function

from math_utils import square

print(square(4))

Output

16

3. Import Multiple Functions

from math_utils import add, square

result = add(5, square(2))
print(result)

Output

9

Import Variations & Aliases

1. Module Aliases (for shorter names)

import math_utils as mu

print(mu.add(6, 7))

2. Function Aliases

from math_utils import square as sq

print(sq(8))

3. Import All (not recommended)

from math_utils import *
print(add(1, 2))
print(square(3))
Note: from ... import * pollutes your namespace and can overwrite existing names. Use with care.

Comparison Table: Import Styles

Pattern Import Example How to Use Best For
Whole module 
import math_utils

math_utils.add(x, y)
Reusing many functions, clear code
Specific function 
from math_utils import square

square(10)
Simpler syntax, importing just what you need
With alias 
import math_utils as mu

mu.add(3, 6)
Shorter names, avoiding conflicts
Import all functions 
from math_utils import *

add(1, 2)
square(4)
Quick scripts; avoid in large projects

Useful Tips

  • File must be in the same directory or Python path: Otherwise, you’ll get a ModuleNotFoundError.
  • No .py in module name: Just use the filename (e.g., my_utils not my_utils.py).
  • Prefer explicit imports: Use from ... import or import ... as ... for clarity and maintainability.
  • Reload after changes: If you edit a module and are using an interactive session, you may need to restart Python or use importlib.reload().
  • Avoid circular imports: Structure your modules so that files do not import each other in a loop.
  • Packages and directories: Use import package.module when organizing code in folders (add an __init__.py file to the folder).

Conclusion

Using import in Python is the foundation of writing organized, reusable, and maintainable code. Break your code into modules, import what you need, and use clear names for robust scripts and scalable projects.

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