Running Python Scripts (REPL, .py Files)

Python is a versatile language that provides multiple ways to execute code. The two most common methods are using the REPL (Read-Eval-Print Loop) for interactive execution and running standalone .py files for scripts. In this article, we will explore both approaches with examples.

1. REPL (Read-Eval-Print Loop)

The Python REPL is an interactive environment where you can execute Python commands one line at a time. It is ideal for experimenting with code snippets and debugging.

How to Use REPL

  • Open a terminal or command prompt.
  • Type python or python3 and press Enter.
  • You will enter the interactive mode, where you can execute Python commands.
          
            # Example 1: Basic commands in REPL
            >>> print("Hello, REPL!")
            Hello, REPL!

            >>> x = 10
            >>> y = 20
            >>> print("Sum:", x + y)
            Sum: 30

2. Running .py Files

For larger programs or scripts, it is more convenient to write code in a file with the .py extension and execute it as a standalone program.

How to Create and Run a .py File

  • Create a new file with a .py extension, for example, script.py.
  • Write your Python code in the file.
  • Run the file from the terminal using the command: python script.py
          
            # Example 2: script.py
            def greet(name):
                return f"Hello, {name}!"

            print(greet("World"))

Output when you run python script.py:

          Hello, World!

3. Benefits of REPL

Using REPL is advantageous for quick testing and debugging. For example, you can immediately check the results of calculations or test a function.

          
            >>> def square(n):
            ...     return n * n
            ...
            >>> square(4)
            16

4. Benefits of .py Files

Using .py files is more suitable for developing full programs or scripts that you want to save and reuse.

          
            # Example 3: script.py with reusable functions
            def add(a, b):
                return a + b

            if __name__ == "__main__":
                result = add(5, 7)
                print("Result:", result)

Output when running the script:

          Result: 12

5. Combining Both Approaches

You can use REPL to test parts of a program and then integrate the tested code into a .py file for larger projects.

          
            >>> def multiply(a, b):
            ...     return a * b
            ...
            >>> multiply(3, 4)
            12

After testing, you can add the multiply function to a script file.

Conclusion

Python provides flexibility in executing code through REPL for interactive use and .py files for full programs. Each method has its own advantages, and understanding when to use them can enhance your programming workflow.




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