Here are common Python interview questions categorized by difficulty and topic, with detailed explanations and examples.

Answer: Lists are mutable (can be modified), while tuples are immutable (cannot be changed after creation). Lists use [] syntax, tuples use ().

list_example = [1, 2, 3]
list_example[0] = 99  # ✅ OK

tuple_example = (1, 2, 3)
# tuple_example[0] = 99  # ❌ TypeError!

Answer: Python determines variable types at runtime, not at compile time. A variable can hold different types at different points in execution.

x = 10        # int
x = "hello"   # str — no error!
x = [1, 2, 3] # list

Answer: == checks value equality (same content), is checks identity (same object in memory).

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

print(a == b)  # True (same values)
print(a is b)  # False (different objects)
print(a is c)  # True (same object)

Answer: Decorators are functions that modify the behavior of other functions. They wrap the original function with additional logic.

def timer(func):
    def wrapper(*args, **kwargs):
        import time
        start = time.time()
        result = func(*args, **kwargs)
        print(f"Took {time.time() - start:.2f}s")
        return result
    return wrapper

@timer
def slow_function():
    import time
    time.sleep(1)

Answer: The GIL is a mutex that allows only one thread to execute Python bytecode at a time. This makes Python threads unsuitable for CPU-bound tasks but fine for I/O-bound tasks. Use multiprocessing for CPU-intensive work.

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __str__(self):
        return f"({self.x}, {self.y})"  # For users

    def __repr__(self):
        return f"Point({self.x!r}, {self.y!r})"  # For developers

p = Point(3, 4)
print(p)        # (3, 4) — __str__
repr(p)         # 'Point(3, 4)' — __repr__

Answer: Python uses reference counting (each object tracks how many references point to it) and a garbage collector (handles circular references). Objects are freed when their reference count reaches zero.

Answer: MRO determines the order in which classes are searched when resolving a method. Python uses C3 linearization. Use ClassName.__mro__ to see the order.

Answer: Metaclasses are classes of classes. They control how classes are created and behave. type is the default metaclass.

class Singleton(type):
    _instances = {}
    def __call__(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = super().__call__(*args, **kwargs)
        return cls._instances[cls]

class Database(metaclass=Singleton):
    pass

Answer: Context managers handle setup/cleanup automatically. Implement __enter__ and __exit__ or use @contextmanager.

# Method 1: Slicing
s[::-1]

# Method 2: reversed()
''.join(reversed(s))

# Method 3: Loop
result = ""
for char in s:
    result = char + result

def find_duplicates(lst):
    seen = set()
    duplicates = set()
    for item in lst:
        if item in seen:
            duplicates.add(item)
        seen.add(item)
    return list(duplicates)

1. Explain your thinking before writing code
2. Consider edge cases — empty input, large input, invalid input
3. Analyze time and space complexity after writing
4. Write clean, readable code with meaningful variable names
5. Test your solution with sample inputs mentally