Interview question

What is the difference between mutable and immutable objects in Python? Python में mutable और immutable objects में क्या अंतर है?

Answer

Mutable	Immutable
list, dict, set	int, float, str, tuple, frozenset, bool
Can be changed in place	Cannot be changed after creation

# Mutable - list changes in place, same object id
my_list = [1, 2, 3]
print(id(my_list))
my_list.append(4)
print(id(my_list))  # SAME id - modified in place

# Immutable - string 'change' actually creates a NEW object
s = 'hello'
print(id(s))
s = s + ' world'
print(id(s))  # DIFFERENT id - new string object created

# Common gotcha: mutable default arguments
def add_item(item, items=[]):  # DANGEROUS - default list is shared across calls!
    items.append(item)
    return items

print(add_item('a'))  # ['a']
print(add_item('b'))  # ['a', 'b'] - unexpected! Same default list reused

# Fix - use None as default, create new list inside
def add_item_safe(item, items=None):
    if items is None:
        items = []
    items.append(item)
    return items

Mutable	Immutable
list, dict, set	int, float, str, tuple
जगह पर बदल सकते हैं	Creation के बाद बदल नहीं सकते

my_list = [1, 2, 3]
print(id(my_list))
my_list.append(4)
print(id(my_list))  # SAME id

s = 'hello'
print(id(s))
s = s + ' world'
print(id(s))  # अलग id - नया object

# Common gotcha: mutable default arguments
def add_item(item, items=[]):  # खतरनाक!
    items.append(item)
    return items

print(add_item('a'))  # ['a']
print(add_item('b'))  # ['a', 'b'] - अनपेक्षित!

# Fix
def add_item_safe(item, items=None):
    if items is None:
        items = []
    items.append(item)
    return items

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