Python Foundations & Execution Model

1. How Python Runs Your Code#

Unlike compiled languages (like C or Go) or purely interpreted languages, Python compiles source code into bytecode (.pyc), which is executed by the Python Virtual Machine (PVM):

  [ Source Code (.py) ]
            |
            v  (Compilation step)
    [ Bytecode (.pyc) ]
            |
            v  (Interpretation)
[ Python Virtual Machine (PVM) ]
            |
            v
     [ Machine Code ]

You can inspect this bytecode directly using Python's built-in dis module:

import dis
 
def calculate_discount(price: float, discount: float) -> float:
    return price * (1.0 - discount)
 
dis.dis(calculate_discount)

2. Variables are Names, Not Buckets#

In many languages, a variable is a memory box holding a value. In Python, variables are pointer labels attached to objects in the heap:

a = [1, 2, 3]
b = a
b.append(4)
 
print(a)  # Output: [1, 2, 3, 4] — both point to the same memory identity!
print(id(a) == id(b))  # True

Understanding this distinction is the key to mastering argument passing, mutation, and performance optimization in Python.