How can I source a Python file from another Python file?

In Python, sourcing one Python file from another enables code reuse and modular programming. This article explores different methods to import and use Python files in your scripts.

Understanding Python File Importing

Python importing allows you to use functions, classes, and variables defined in one file within another. This promotes code reusability and helps organize code into logical modules based on functionality.

Using the import Statement

The import statement is the most common way to include external Python files or modules in your script.

Following is the syntax ?

import module_name

Example

Here's a basic example importing the built-in math module ?

import math
print(math.sqrt(16))
print(math.pi)

4.0
3.141592653589793

For custom modules, first create a file called math_operations.py ?

# math_operations.py
def add(a, b):
    return a + b

def subtract(a, b):
    return a - b

Now in main.py, import and use the functions ?

# main.py
import math_operations

result = math_operations.add(5, 4)
print(result)

result = math_operations.subtract(10, 6)
print(result)

9
4

Using from...import Statement

The from...import statement imports specific functions, classes, or variables directly, allowing you to use them without the module prefix.

Here is the syntax ?

from module_name import attribute_name

Example

Create math_operations.py with additional functions ?

# math_operations.py
def multiply(a, b):
    return a * b

def divide(a, b):
    return a / b

def power(a, b):
    return a ** b

Import only specific functions in main.py ?

# Simulating the import (functions defined inline for demo)
def multiply(a, b):
    return a * b

def divide(a, b):
    return a / b

# Using the functions directly
result = multiply(2, 8)
print(result)

result = divide(10, 5)
print(result)

16
2.0

Using import...as Statement

The import...as statement imports a module with an alias, helping to shorten long module names and avoid naming conflicts.

Following is the syntax ?

import module_name as alias

Example

Import math_operations with an alias ?

# Simulating import with alias
def add(a, b):
    return a + b

def subtract(a, b):
    return a - b

# Using alias-like approach
math_ops_add = add
math_ops_subtract = subtract

result = math_ops_add(3, 8)
print(result)

result = math_ops_subtract(15, 9)
print(result)

11
6

Using exec() for Dynamic Imports

The exec() function dynamically executes Python code, including imports. This is useful for conditional imports at runtime.

Example

Dynamically import based on runtime conditions ?

# Simulate dynamic import behavior
import math

# Dynamic module selection
module_name = "math"

if module_name == "math":
    result = math.sqrt(25)
    print(f"Square root of 25: {result}")
    
# You can also use exec() for dynamic imports
exec("import random")
print(f"Random number: {random.randint(1, 10)}")

Square root of 25: 5.0
Random number: 7

Comparison of Import Methods

Conclusion

Use import for full module access, from...import for specific functions, and import...as for aliases. Reserve exec() for dynamic runtime imports when the module name isn't known beforehand.