Python inner working

How Python Works Internally (Inner Workings of Python)

Python is an interpreted, dynamically-typed, and high-level language. Let’s break down its inner workings step by step.

1. Python Code Execution Process

When you write and run a Python script (.py file), Python internally goes through several steps:

1️⃣ Source Code (.py file)

You write Python code in a .py file.
Example:
```
  pythonCopyEditprint("Hello, World!")
```

2️⃣ Lexical Analysis (Tokenizer)

Python breaks the code into tokens (small meaningful units).

Example: print("Hello, World!") is broken into:

  csharpCopyEdit[PRINT, STRING_LITERAL("Hello, World!"), NEWLINE]

3️⃣ Parsing (Syntax Analysis)

Python checks the syntax using the tokens and creates a parse tree.
If there are syntax errors, Python throws an error.

4️⃣ Abstract Syntax Tree (AST)

The parse tree is converted into an AST (simplified tree structure).

Example:

  scssCopyEditAST of print("Hello"):
    ├── Print
    ├── String("Hello")

5️⃣ Bytecode Generation (.pyc file)

The AST is converted into Python Bytecode (.pyc), which is a low-level, platform-independent set of instructions.

Example of bytecode:

  bashCopyEditLOAD_GLOBAL 0 (print)
  LOAD_CONST 1 ('Hello, World!')
  CALL_FUNCTION 1
  POP_TOP

6️⃣ Python Virtual Machine (PVM)

The bytecode is executed by the Python Virtual Machine (PVM).
The PVM is responsible for running your Python program.

2. Python Memory Management

Python manages memory automatically using: ✅ Reference Counting
✅ Garbage Collection (GC)
✅ Dynamic Memory Allocation

(a) Reference Counting

Python keeps track of how many times an object is referenced.

pythonCopyEditx = "Hello"  # Reference count = 1
y = x        # Reference count = 2
del x        # Reference count = 1 (but object still exists)

If reference count reaches zero, Python deletes the object.

(b) Garbage Collection (GC)

Python has an automatic garbage collector that removes unused objects.
Uses Generational Garbage Collection to manage memory efficiently.

(c) Memory Allocation (Heap & Stack)

Stack Memory: Stores function calls and local variables.
Heap Memory: Stores objects like lists, dictionaries, and user-defined objects.

3. Python Internals: Objects & Variables

In Python, everything is an object (numbers, strings, functions, etc.).

pythonCopyEditx = 10
print(id(x))  # Returns memory address of x

Variables in Python are references (pointers) to objects in memory.

4. Python's Global Interpreter Lock (GIL)

Python uses the GIL, which means:

Only one thread can execute Python bytecode at a time.
This can limit multi-threading performance.
Solution? Use multiprocessing instead of threading for CPU-intensive tasks.

5. Python's Built-in Data Structures

Python provides efficient built-in data structures:

Lists ([]) → Dynamic arrays
Tuples (()) → Immutable sequences
Dictionaries ({}) → Hash tables (key-value pairs)
Sets ({}) → Unordered collections of unique elements

6. Python's Interpreter

Python has different implementations:

CPython (Default, written in C)
PyPy (Uses JIT for faster execution)
Jython (Runs on Java Virtual Machine)
IronPython (Runs on .NET framework)

Summary: Python's Inner Workings

1️⃣ Python converts source code → tokens → AST → bytecode
2️⃣ Bytecode runs on Python Virtual Machine (PVM)
3️⃣ Memory management uses reference counting & garbage collection
4️⃣ GIL restricts threading, so multiprocessing is preferred
5️⃣ Everything in Python is an object