What is Python Interpreter

A Python Interpreter is the program that reads and executes Python code. It translates your Python instructions into machine-readable form line by line, so the computer can understand and run them.

When you run a Python program, code passes through Python Interpreter, which is responsible for:

• Checking your code for errors.
• Converting it into an intermediate form called bytecode.
• Sending it to the Python Virtual Machine (PVM) for execution.

Working of Interpreter

Let’s understand the step-by-step process of how your Python code runs:

1. Python Source Code (.py file): You write your program in a .py file.
2. Parser and AST (Syntax Check -> Abstract Syntax Tree): Python checks the code for syntax errors and converts it into an AST (Abstract Syntax Tree), which represents the program structure.
3. Bytecode (.pyc file in __pycache__): The AST is compiled into bytecode, a low-level instruction set. This bytecode may also be saved in the __pycache__ folder for reuse.
4. Python Virtual Machine (Executes Bytecode): The PVM executes the bytecode line by line and translates it into machine instructions.
5. Output (Result on Screen): Finally, the program’s result is shown on the screen (for example, via print()).

To visualize this at a high level, here’s a simple diagram of how an interpreter processes your code:

Example

This program takes two inputs as a and b and prints sum in the third variable which is c. It follows sequential as well as functional execution of programs

a = 3 b = 7 c = a + b print(c) 

10

Behind the scenes, here’s what happens:

• The interpreter reads each line.
• Converts it into tokens (a, =, 3, +, b, etc.).
• Builds an AST and then bytecode.
• PVM executes the bytecode and displays 10.

Different Python Interpreter Variants

The default and most widely used interpreter is called CPython, because it is implemented in the C programming language.

• CPython is the official Python interpreter you download from python.org
• Every time you type python script.py, you are using CPython unless you install another interpreter.

Other variants of Python interpreters include:

• PyPy: faster, uses JIT (Just-In-Time compilation).
• Stackless Python: optimized for concurrency.
• MicroPython: lightweight, designed for microcontrollers.
• Jython: runs on the Java platform.
• IronPython: runs on .NET framework.

Difference between Compilers and Interpreters

It’s important to understand how an interpreter differs from a compiler:

Advantages

• Easy debugging: errors are shown immediately line by line.
• Flexible and portable: works across platforms without recompiling.
• No need for separate compilation: just run the script directly.
• Supports dynamic typing: variable types don’t need to be declared.

Disadvantages

• Slower than compiled languages (because it executes line by line).
• Higher memory usage.
• Not ideal for low-level programming (like OS kernels or device drivers).