itertools and functools

The itertools module builds efficient loops for you: chain joins iterables end to end, combinations and permutations enumerate choices, groupby groups neighbouring items, and count counts forever. The functools module has tools for functions: reduce folds a list into one value, partial pre-fills some arguments, and lru_cache remembers results.

How it reads

• combinations(items, 2) gives every pair, ignoring order
• reduce carries an accumulator through the whole list
• partial(power, exp=2) is a new function with exp already filled in

Cloud tip: itertools functions return lazy iterators. Wrap them in list() when you want to see every value.