Is Python Compiled or Interpreted?

Python is an interpreted programming language. However, when we want to check whether Python is compiled or interpreted can be a bit confusing. Let's dive into a detailed explanation to understand the inner workings of Python's execution model and how it combines aspects of compilation and interpretation.

Interpreted languages are typically executed directly by an interpreter without a separate compilation step. In contrast, compiled languages go through a compilation process where the source code is translated into machine code or an intermediate representation before execution. However, Python's execution model is a blend of both interpretation and compilation.

At a high level, Python source code is written in human-readable form and saved with a .py extension. When we run a Python program, the following steps take place:

Parsing

The Python interpreter reads the source code and parses it into a form called an Abstract Syntax Tree (AST). The parser analyzes the structure and syntax of the code, ensuring it is valid according to Python's grammar rules ?

import ast

code = "x = 5 + 3"
tree = ast.parse(code)
print(ast.dump(tree, indent=2))

Module(
  body=[
    Assign(
      targets=[
        Name(id='x', ctx=Store())],
      value=BinOp(
        left=Constant(value=5),
        op=Add(),
        right=Constant(value=3)))],
  type_ignores=[])

Bytecode Compilation

Once the parsing is complete, the Python interpreter compiles the AST into an intermediate form called bytecode. Bytecode is a low-level representation specific to the Python Virtual Machine (PVM), rather than being tied to any particular hardware or operating system.

Bytecode is a compact and platform-independent representation of the original source code. It consists of instructions that the PVM can execute directly ?

import dis

def add_numbers(a, b):
    return a + b

dis.dis(add_numbers)

  2           0 LOAD_FAST                0 (a)
              2 LOAD_FAST                1 (b)
              4 BINARY_ADD
              6 RETURN_VALUE

Execution

The bytecode is executed by the Python interpreter's execution loop. The interpreter reads each bytecode instruction, performs the necessary operations, and updates the program state accordingly.

During execution, the Python interpreter employs various built-in functions and modules to provide a wide range of functionality. The interpreter also manages memory allocation, object creation, and handles exceptions that occur during execution.

Dynamic Typing and Late Binding

Python is dynamically typed, which means that variable types are determined at runtime. This allows for greater flexibility but requires interpreting the code to determine types and bind variables to objects ?

x = 5        # x is an integer
print(type(x))

x = "hello"  # x is now a string
print(type(x))

<class 'int'>
<class 'str'>

Benefits of Python's Execution Model

• Ease of Development Python's interpreted nature makes it excellent for rapid development and prototyping. Developers can write code and immediately see results without a separate compilation step.

• Cross-Platform Portability Python's bytecode is platform-independent, meaning programs can run on different operating systems as long as a compatible Python interpreter is available.

• Runtime Debugging and Interactivity The interactive shell (REPL) enables exploration and experimentation with immediate feedback.

• Dynamic Code Execution Python supports dynamic code execution, enabling powerful metaprogramming techniques and dynamic module loading.

Python Implementations

It's worth noting that Python implementations can vary. The reference implementation, known as CPython, executes Python code by interpreting the bytecode. Other implementations like PyPy employ just-in-time (JIT) compilation techniques to optimize bytecode execution.

Conclusion

Python is an interpreted language with a bytecode compilation step. It parses source code, compiles it into bytecode, and executes the bytecode using an interpreter. This hybrid approach provides Python with its characteristic balance of flexibility, portability, and ease of development.