1. Core Python

A fast overview of everyday Python building blocks: types, truthiness, slicing, and small-but-crucial idioms you use constantly.

Q1 What are the main built-in data types?

Answer: Python has numbers (int, float, complex), strings (str), booleans (bool), binary types (bytes, bytearray, memoryview), ranges (range), and collections. None represents the absence of a value.

Explanation:

• Strings: Immutable sequences of characters. Use f-strings (f"Hello, {name}") for easy formatting.

• Collections:

  • list [1, 2]: Mutable (changeable) and ordered.

  • tuple (1, 2): Immutable (cannot be changed) and ordered.

  • dict {"k": 1}: Mutable key-value pairs, ordered by insertion (Python 3.7+).

  • set {1, 2}: Mutable, unordered, and contains unique elements.

  • frozenset frozenset({1, 2}): Immutable set; hashable and usable as a dictionary key.

Q2 When would you use a tuple instead of a list?

Answer: Use a tuple for data that should not change, like coordinates (x, y). Because they are immutable, tuples are hashable and can be used as dictionary keys, whereas lists cannot.

Q3 What does it mean for a value to be "falsy"?

Answer: In a boolean context (like an if statement), some values evaluate to False. These are called "falsy" values. They include 0, 0.0, empty strings '', empty collections ([], {}, (), set()), None, and False itself. All other values are "truthy".

Q4 How do you slice strings and sequences?

Answer: Use sequence[start:stop:step]; negative indices count from the end.

s = "abcdef"
s[1:4]     # 'bcd'
s[:3]      # 'abc'
s[-2:]     # 'ef'
s[::2]     # 'ace'

Explanation: Slicing returns a new object of the same type; out-of-range indices are clamped, not errors.

Q5 What’s the difference between str and bytes?

Answer: str is text (Unicode), bytes is raw 8-bit data. Convert with .encode()/.decode().

text = "Привет"
data = text.encode("utf-8")   # bytes
back = data.decode("utf-8")   # str

Q6 How does iterable unpacking work?

Answer: You can unpack sequences into names; use *rest to capture remaining items.

a, b = (1, 2)
first, *middle, last = [10, 20, 30, 40]   # first=10, middle=[20,30], last=40