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itertools

module

Building blocks for lazy iterators: chaining, slicing, grouping, permutations and endless counters.

Syntax

import itertools

The functions in itertools return lazy iterators: nothing is computed until the result is consumed, and it can be consumed only once, so a second list() gives an empty list. count and cycle never end, so bound them with islice or takewhile. A common mistake is groupby on unsorted data: it only merges adjacent equal keys.

Examples

import itertools
it = itertools.chain([1, 2], (3,))
print(list(it), list(it))  # → [1, 2, 3] [] — итератор одноразовый
print(list(itertools.islice(itertools.count(10), 3)))  # → [10, 11, 12]
print([k for k, _ in itertools.groupby('aabaa')])  # → ['a', 'b', 'a']

See also

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