Python Series – Part 9: How Python Executes Code | Step-by-Step Execution Model

🎉 Introduction

"Python code likhna easy hai… lekin kya aapko pata hai Python us code ko execute kaise karta hai?

Variables memory me kaise jaate hain? Function call hota hai to kya hota hai? Agar koi variable bina define kiye use ho jaaye to Python gussa kyun ho jaata hai?

Aaj iss video me hum Python ke dimaag ke andar jaake dekhenge — how Python really executes your code, line by line."

📦 Section 1: Python Execution — Big Picture

"Python interpreter code ko top-to-bottom read karta hai — line-by-line, jaise hum book padhte hain."

Steps:

1. Interpreter file load karta hai
2. Top se bottom tak read hota hai
3. Functions aur classes pehle sirf define hote hain (execute nahi)
4. Function call hone par new execution frame create hota hai call stack par

🔢 Section 2: Let’s Break It Down with an Example

x = 5
 
def greet():
    print("Hello")
 
greet()
print(x)

Execution Steps:

1. x = 5 ➔ memory me Global Scope me store hota hai
2. greet function define hota hai (abhi call nahi hua)
3. greet() call hone par new frame banta hai ➔ "Hello" print
4. x global scope se print hota hai

📂 Section 3: Memory Model (Stack & Heap)

"Python ke memory model me 2 major cheeze hoti hain: Stack aur Heap."

• Heap: Jahan objects, lists, dicts jaise values store hote hain
• Stack: Jahan function call frames aur local variables store hote hain

Example:

def add(a, b):
    return a + b
 
result = add(10, 20)

• add() call hone par stack pe frame banta hai
• a=10, b=20 stack me store hote hain
• Return ke baad frame delete ho jaata hai
• Result heap me value 30 ke reference ke saath store hota hai

📌 Section 4: Why Order Matters in Python

say_hello()
 
def say_hello():
    print("Hi")

"Ye error dega! Kyunki jab interpreter code read kar raha tha, say_hello ka declaration abhi nahi aaya tha."

Lesson:

• Python code line-by-line execute karta hai
• Pehle define karo, baad me use karo

🧪 Section 5: Python Execution with Conditions

x = 10
 
if x > 5:
    def shout():
        print("Big!")
 
shout()

"Function shout tabhi define hota hai jab condition true ho.

Agar condition false hoti to shout naam ka function kabhi banta hi nahi."

Lesson:

• Functions condition ke andar bhi define ho sakte hain
• Definition depends on execution flow

🧬 Section 6: Behind-the-Scenes Function Execution

def greet(name):
    message = f"Hello {name}"
    return message
 
output = greet("DeathCode")

Execution:

1. greet define hota hai
2. greet() call hone par new frame banta hai
3. name="DeathCode", message create hota hai
4. message return hota hai, frame destroy
5. output variable me store

"Har function ka apna ek chhota sa environment ya frame hota hai."

⚠ Section 7: Common Mistakes by Beginners

1. Calling function before defining
2. Using variables before assigning value
3. Confusing global and local variables
4. Not understanding definition time vs execution time

🧹 Section 8: Final Real-life Analogy

"Socho Python ek chef hai.

Uske paas ek recipe (code) hai.

Wo recipe ek-ek step follow karta hai.

Agar kisi step me bola 'add sugar', lekin sugar define nahi hai, to chef confused ho jaayega — jaise Python confused ho jaata hai."

📝 Section 9: Practice Questions

1. What will this code print?

def foo():
    print(x)
 
x = 10
foo()

2. What happens here?

if False:
    def hidden():
        print("You found me!")
 
hidden()

3. Trace this code line-by-line:

def outer():
    x = "outer"
    def inner():
        print(x)
    inner()
 
x = "global"
outer()

4. Create a function that accepts a number and returns double it. Trace memory.

🎤 Outro

"Ab aapko clear ho gaya hoga ki Python ka execution model kaise kaam karta hai!

Agla part hoga advanced Function Parameters in Python — jahan hum sikhenge positional arguments, keyword arguments, default values, *args, **kwargs ka advance breakdown!

Like karo, comment karo, aur subscribe karna mat bhoolna! 💥"