Generator expressions in Python

Lazy comprehensions that compute one item at a time.

readings = [21.5, 19.8, 23.1, 22.4, 18.9]

total = sum(r for r in readings if r > 20)
hottest = max(r for r in readings)
any_cold = any(r < 19 for r in readings)
all_mild = all(15 < r < 25 for r in readings)

squares = (n * n for n in range(1_000_000))
first = next(squares)
second = next(squares)

count = sum(1 for r in readings if r > 20)

How it works

1. sum(r for r in readings if r > 20) never builds a list.
2. any and all short-circuit over the stream.
3. next pulls single values from an endless expression.

Keywords and builtins used here

• all
• any
• for
• if
• max
• next
• range
• sum

The run, in numbers

Lines

12

Characters to type

341

Tokens

103

Three-star pace

100 tpm

At the three-star pace of 100 tokens a minute, this run takes about 62 seconds.

Type this snippet

Step 4 of 4 in Comprehensions, step 4 of 53 in Pythonic Python.

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