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10. Using the Python REPL

1. Introduction​

The Python REPL (Read-Eval-Print Loop) is an interactive shell where you can type Python commands and see results immediately.
It is one of the fastest ways to experiment, test small pieces of code, and learn Python.

2. Starting the REPL​

Open a terminal (Linux/macOS) or Command Prompt (Windows) and type:

python

or, if multiple versions are installed:

python3

You should see something like:

Python 3.12.2 (tags/v3.12.2:...) 
>>>

The >>> prompt means Python is ready for input.

3. Running Basic Commands​

Try typing:

2 + 3

Output:

5

Try another:

print("Hello, Python!")

Output:

Hello, Python!

4. Using Variables​

You can create variables and use them immediately:

x = 10
y = 5
x + y

Output:

15

5. Using Built-in Functions​

The REPL supports all Python functions:

len("Python")

Output:

6

6. Getting Help​

Inside the REPL, type:

help()

This opens an interactive help system.
Type quit to exit help.

You can also get help on a specific function:

help(len)

7. Exiting the REPL​

To exit, type:

exit()

or press:

  • Ctrl + Z then Enter (Windows)
  • Ctrl + D (Linux/macOS)

8. Useful Tips​

  • Use the arrow keys to scroll through command history.
  • Press Tab to autocomplete variable names and functions.
  • Use Ctrl + L (Linux/macOS) or cls command on Windows to clear the screen.

9. Why Use the REPL?​

  • Great for learning Python.
  • Quick way to test ideas.
  • Lightweight compared to opening an IDE.

10. Next Steps​

✅ You now know how to use the Python REPL to run code interactively.
In the next chapter, we’ll learn how to run Python scripts from the command line.