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36 lines
884 B
36 lines
884 B
3 years ago
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from itertools import filterfalse
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from typing import (
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Callable,
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Iterable,
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Iterator,
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Optional,
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Set,
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TypeVar,
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Union,
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)
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# Type and type variable definitions
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_T = TypeVar('_T')
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_U = TypeVar('_U')
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def unique_everseen(
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iterable: Iterable[_T], key: Optional[Callable[[_T], _U]] = None
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) -> Iterator[_T]:
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"List unique elements, preserving order. Remember all elements ever seen."
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# unique_everseen('AAAABBBCCDAABBB') --> A B C D
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# unique_everseen('ABBCcAD', str.lower) --> A B C D
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seen: Set[Union[_T, _U]] = set()
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seen_add = seen.add
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if key is None:
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for element in filterfalse(seen.__contains__, iterable):
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seen_add(element)
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yield element
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else:
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for element in iterable:
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k = key(element)
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if k not in seen:
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seen_add(k)
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yield element
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