How to call Python module from command line?

To call a Python module from the command line, you can use the python command followed by flags like -m or -c, or run the script file directly. This article covers the most common approaches with practical examples.

Running a Module with python -m

The -m flag tells Python to run a module by its module name (without the .py extension). Python searches sys.path for the module and executes its __main__ block −

~$ python -m module_name

For example, to run the built-in json.tool module for formatting JSON −

~$ echo '{"name":"Alice"}' | python -m json.tool
{
    "name": "Alice"
}

For your own modules, ensure the file has an if __name__ == "__main__" guard so that code runs only when the module is executed directly.

Running a Script File Directly

The simplest approach is to run a .py file directly and use sys.argv to accept command-line arguments ?

Example

Create a file called my_script.py ?

import sys

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

if __name__ == "__main__":
    if len(sys.argv) != 3:
        print("Usage: python my_script.py arg1 arg2")
    else:
        arg1 = int(sys.argv[1])
        arg2 = int(sys.argv[2])
        print(multiply(arg1, arg2))

Run it from the command line ?

~$ python my_script.py 5 7
35

Calling a Specific Function with python -c

The -c flag lets you pass a Python command as a string. This is useful for calling a specific function from a module without modifying the file ?

Example

Create a file called example.py ?

def add_numbers(num1, num2):
    return num1 + num2

Call the function from the command line ?

~$ python -c "import example; print(example.add_numbers(2, 3))"
5

This imports the example module and calls add_numbers with arguments 2 and 3, then prints the result.

Example: Calling a Function with String Arguments

Given a file greetings.py ?

def greet(name):
    return f"Hello, {name}!"

Call it from the command line ?

~$ python -c "import greetings; print(greetings.greet('Alice'))"
Hello, Alice!

Conclusion

Use python script.py with sys.argv for scripts that accept arguments, python -m module_name to run a module by name, and python -c for quick one-off function calls. Always include an if __name__ == "__main__" guard in modules meant to be both imported and executed directly.