Day 31 :Not Understanding Variable Scope

 

🐍 Python Mistakes Everyone Makes ❌

Day 31: Not Understanding Variable Scope

Variable scope decides where a variable can be accessed or modified. Misunderstanding it leads to confusing bugs and unexpected results.

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❌ The Mistake

x = 10

def update():
    x = x + 1
    print(x)

update()

This raises an error.

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❌ Why This Fails

• Python sees x inside the function as a local variable

• You’re trying to use it before assigning it

• The outer x is not automatically modified

• Result: UnboundLocalError

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✅ The Correct Ways

Option 1: Use global (use sparingly)

x = 10

def update():
    global x
    x += 1

update()
print(x)

Option 2 (Recommended): Pass and return

def update(x):
    return x + 1

x = 10
x = update(x)
print(x)

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✔ Scope Rules in Python (LEGB)

• Local – inside the function

• Enclosing – inside outer functions

• Global – module-level

• Built-in – Python keywords

Python searches variables in this order.

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🧠 Simple Rule to Remember

✔ Variables assigned inside a function are local by default
✔ Read-only access is allowed, modification is not
✔ Pass values instead of relying on globals

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🐍 Understanding scope saves hours of debugging.