2. Python Under the Hood

To be an expert, you must understand the tool.

1. Everything is an Object

In languages like C, a variable can store a raw integer value directly in a memory address. In Python, everything—integers, strings, functions—is an Object.

• Header: Contains metadata (Reference Count, Type Pointer).
• Value: The actual data.

2. The Id Function (Memory Address)

You can see where an object literally lives in your RAM using id().

python
x = 10
print(hex(id(x)))  # 0x100a4... (Memory Address)

3. Variables are Labels, Not Boxes

This is the most critical concept to unlearn from other languages.

• Mental Model C++: A variable is a box. int a = 10 puts 10 into box 'a'.
• Mental Model Python: A variable is a Name Tag. a = 10 sticks the tag 'a' onto the object 10.

python
a = [1, 2, 3]
b = a

We did not copy the list. We just put a second sticker (b) on the same object.

4. Mutability (The Source of Bugs)

• Immutable (Safe): Strings, Tuples, Integers. You cannot change the object content. modifying it creates a new object.
• Mutable (Dangerous): Lists, Dictionaries. You change the object in place.

python
def append_item(lst):
    lst.append(99) # This modifies the ORIGINAL list outside the function!

my_list = [1]
append_item(my_list)
print(my_list) # [1, 99] <- Side Effect!

Engineering Rule: Prefer Immutability to avoid side-effects.