Python Knowledge

Question 1

How to reverse a string (x) in Python?

Answer 1

x[::-1]

Question 2

List vs. Tuple

Answer 2

Definition:
Lists are mutable sequences, while tuples are immutable sequences.

• Lists can be changed in-place; tuples cannot.
• Tuples can be used as dictionary keys (hashable), whereas lists cannot.

Question 3

List Comprehensions

Answer 3

Definition:
A concise syntax for creating lists from iterables with optional conditions.

• Written as:
  [expression for item in iterable if some condition]

e.g., Increment item when <9
[item+1 for item in items if item<9]

• Improves readability and can be more efficient than equivalent for-loops.

Question 4

Generators

Answer 4

Definition:
Functions that use yield to produce a sequence of values lazily.

• Saves memory by not storing the entire sequence in memory.
• Can be iterated over just once (stateful).

Question 5

GIL (Global Interpreter Lock)

Answer 5

Definition:
A mutex in CPython preventing multiple native threads from executing Python bytecodes simultaneously.

• Affects CPU-bound multi-threading (no true parallelism).
• I/O-bound tasks can still benefit from threading.

Question 6

Decorator

Answer 6

Definition:
A callable (function or class) that takes another function and extends or modifies its behavior.

• Commonly used for logging, synchronization, caching, or authentication.
• Syntax: @my_decorator above the function definition.

Question 7

__init__ vs. __new__

Answer 7

Definition:
__init__ initializes an instance after it’s created; __new__ actually creates the instance (rarely overridden).

__init__ is used for most initialization tasks.

__new__ is useful for customizing the creation of immutable types or singletons.

Question 8

Python Memory Management

Answer 8

Definition:
Uses reference counting and a cyclic garbage collector to free unreachable objects.

• The gc module handles detection and cleanup of reference cycles.
• Reference counting is immediate for zero-count objects.