How to Run Another Python Script from Python Easily

You can run another Python script from your Python code using the subprocess.run() function to execute it as a separate process, or by importing the script as a module and calling its functions directly. The subprocess method runs the script like a command, while importing lets you reuse code inside the script.

Syntax

Here are two common ways to run another Python script:

• Using subprocess: Runs the script as a separate process.
• Using import: Runs the script by importing it as a module.

subprocess syntax:

subprocess.run(["python", "script_name.py"])

import syntax:

import script_name
script_name.some_function()

python

import subprocess

# Run script as a separate process
subprocess.run(["python", "script_name.py"])

# Or import and call functions
import script_name
script_name.some_function()

Example

This example shows how to run a script named hello.py from another script. The hello.py script prints a greeting. The main script runs it using subprocess.run() and also imports it to call a function.

python

# hello.py

def greet():
    print("Hello from hello.py!")

if __name__ == "__main__":
    greet()

# main.py
import subprocess
import hello

print("Running hello.py using subprocess:")
subprocess.run(["python", "hello.py"])

print("\nCalling greet() from imported hello module:")
hello.greet()

Output

Running hello.py using subprocess:
Hello from hello.py!

Calling greet() from imported hello module:
Hello from hello.py!

Common Pitfalls

1. Wrong Python executable: Use sys.executable instead of just "python" to ensure the correct Python version runs the script.

2. Importing scripts with side effects: If the script runs code on import, use if __name__ == "__main__" guard to avoid unwanted execution.

3. File paths: Make sure the script path is correct or use absolute paths to avoid "file not found" errors.

python

import subprocess
import sys

# Correct way to run another script with current Python
subprocess.run([sys.executable, "hello.py"])

# In hello.py, protect code that runs on import
if __name__ == "__main__":
    greet()

Quick Reference

Summary of ways to run another Python script:

Method	Description	Use Case
subprocess.run()	Runs script as a separate process	When you want to run script independently and capture output
import module	Imports script as a module to reuse functions	When you want to call specific functions or reuse code
exec(open().read())	Executes script code in current script	Less common, can cause namespace issues

Key Takeaways

Use subprocess.run([sys.executable, 'script.py']) to run another script as a separate process safely.

Import scripts as modules to reuse functions without running the whole script.

Always protect executable code in scripts with if __name__ == '__main__' to avoid unwanted runs on import.

Check file paths and Python executable to avoid common errors.

Choose subprocess for independent runs and import for code reuse.