1. Core Python

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

Question: 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.

Question: 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.

Question: 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".

Question: 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.

Question: 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

Question: 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