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Chapter 8

Comprehensions and built-ins

Comprehensions build a list, set or dict in one line: a loop, and maybe a test, inside brackets. Python also ships with built-in functions that save you writing loops at all: sum(), sorted(), max(), enumerate() and zip(). This chapter covers both, so you can read the short, tidy code experienced Python programmers write, and spot when len() is given something with no length.

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  1. What does this list comprehension print?[0, 2, 4]
  2. What does the if in this list keep?[0, 3, 6]
  3. What does this dict comprehension print?{'hi': 2, 'sea': 3}
  4. What does sum() print for this list?10
  5. What does sorted() print with reverse=True?[3, 2, 1]
  6. What does enumerate() pair each letter with?[(0, 'a'), (1, 'b')]
  7. What does zip() make of two lists?[(1, 'a'), (2, 'b')]
  8. What does max() with key=len print?banana
  9. Fill the blank in this list comprehensionfor
  10. What's wrong here: len() of a number?TypeError
  11. Built-in that pairs items from two listszip
  12. Built-in that gives each item with its positionenumerate

Image credits

  • What does this list comprehension print?: Brain Zap, CC0 1.0 Source
  • What does the if in this list keep?: Brain Zap, CC0 1.0 Source
  • What does this dict comprehension print?: Brain Zap, CC0 1.0 Source
  • What does sum() print for this list?: Brain Zap, CC0 1.0 Source
  • What does sorted() print with reverse=True?: Brain Zap, CC0 1.0 Source
  • What does enumerate() pair each letter with?: Brain Zap, CC0 1.0 Source
  • What does zip() make of two lists?: Brain Zap, CC0 1.0 Source
  • What does max() with key=len print?: Brain Zap, CC0 1.0 Source
  • Fill the blank in this list comprehension: Brain Zap, CC0 1.0 Source
  • What's wrong here: len() of a number?: Brain Zap, CC0 1.0 Source