Function Scope, Closures and Default Arguments Short Notes for GATE DA: Concepts, Formulas, Worked Examples & Practice

Function Scope, Closures and Default Arguments short notes for GATE DA: 2 study cards covering concepts, formulas, shortcuts and exam traps, plus solved practice questions.

Mutable Defaults Cheat Sheet

Non-Negotiable Rules

Default arguments are evaluated once at definition time.
Immutable defaults (int, str, tuple) are always safe.
Mutable defaults (list, dict, set) are shared across all calls.
Mutating a mutable default (e.g., .append()) changes it for all future calls.
Reassigning a mutable default (e.g., lst = []) does not change the shared default.

Quick Diagnostic Flow

See a function with a default argument?
    |-- Is the default immutable (int, string, None)?
    |     -> Safe. Each call gets its own value.
    |
    |-- Is the default mutable (list, dict)?
    |     |-- Does the body mutate it (e.g., .append)?
    |     |     -> Trap! State is shared across calls.
    |     |
    |     |-- Does the body reassign it (e.g., lst = ...)?
    |           -> Safe. The default object is not mutated.

The Golden Fix

Always use None for mutable defaults:

def func(x, my_list=None):
    if my_list is None:
        my_list = []

Core Rules for Closures

Final Revision Checklist:

Definition: Nested function + enclosed reference + returned by outer function.
Isolation: f1 = outer() and f2 = outer() have strictly separate memory states.
Mutation: Mutable types (lists) can be modified in-place directly.
Rebinding: Immutable types (ints) require the nonlocal keyword to update.
Inspection: Check func.__closure__ to verify a closure exists.
Trap: Loop variables are evaluated at execution time (late binding); use default arguments to force early binding.

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Function Scope, Closures and Default Arguments Short Notes for GATE DA: Concepts, Formulas, Worked Examples & Practice

Function Scope, Closures and Default Arguments short notes for GATE DA: 2 study cards covering concepts, formulas, shortcuts and exam traps, plus solved pract

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