Using the Python Interpreter

Learn how to invoke and use the Python interpreter

The Python interpreter is your gateway to running Python code. This guide covers how to start the interpreter, pass arguments, and understand its interactive mode.

Invoking the Interpreter

The Python interpreter is usually installed as /usr/local/bin/python3.15 on Unix systems. You can start it by typing:

python3.15

On Windows, if you’ve installed Python from the Microsoft Store, use:

python

Or with the py launcher:

py

Exiting the Interpreter

To exit the interpreter:

• Unix/Linux: Press Ctrl-D
• Windows: Press Ctrl-Z then Enter
• All platforms: Type quit()

Command Line Editing

The interpreter supports:

• Interactive line editing
• History substitution
• Code completion on most systems

Test if command line editing works by typing a word and pressing the Left arrow key. If the cursor moves, editing is enabled.

Running Python Scripts

You can run Python code in several ways:

Execute a File

python script.py

Execute a Command

python -c "print('Hello, World!')"

Since Python statements often contain spaces or special characters, quote the entire command.

Execute a Module

python -m http.server

Interactive Mode After Script

Run a script and then enter interactive mode:

python -i script.py

Argument Passing

When you run a Python script, command-line arguments are available in sys.argv:

import sys

print("Script name:", sys.argv[0])
print("Arguments:", sys.argv[1:])

Special cases:

• No script: sys.argv[0] is an empty string
• With -c: sys.argv[0] is '-c'
• With -m: sys.argv[0] is the full module name

Interactive Mode

When you start the interpreter without a script, it enters interactive mode:

$ python3.15
Python 3.15 (default, May 7 2025, 15:46:04)
[GCC 10.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

Prompts

• Primary prompt (>>>): Ready for a new statement
• Secondary prompt (...): Continuation of a multi-line statement

>>> the_world_is_flat = True
>>> if the_world_is_flat:
...     print("Be careful not to fall off!")
...
Be careful not to fall off!

Source Code Encoding

By default, Python source files are treated as UTF-8 encoded. This allows using characters from most languages:

# UTF-8 is the default
name = "François"
greeting = "你好"

Declaring a Different Encoding

To use a different encoding, add a special comment as the first line:

# -*- coding: encoding -*-

Example for Windows-1252:

# -*- coding: cp1252 -*-

With a Shebang Line

If your script starts with a shebang, the encoding goes on the second line:

#!/usr/bin/env python3
# -*- coding: cp1252 -*-

For portable code, stick to UTF-8 encoding and ASCII identifiers even if you can use non-ASCII characters in strings and comments.

Next Steps

Now that you know how to invoke the interpreter, let’s explore Python basics in the Introduction to Python.