mirror of https://github.com/python/cpython
Issue 7764: Improve recipe for itertools.consume().
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@ -641,7 +641,13 @@ which incur interpreter overhead.
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def consume(iterator, n):
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"Advance the iterator n-steps ahead. If n is none, consume entirely."
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collections.deque(islice(iterator, n), maxlen=0)
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# The technique uses objects that consume iterators at C speed.
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if n is None:
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# feed the entire iterator into a zero-length deque
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collections.deque(iterator, maxlen=0)
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else:
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# advance to the emtpy slice starting at position n
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next(islice(iterator, n, n), None)
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def nth(iterable, n, default=None):
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"Returns the nth item or a default value"
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@ -751,3 +757,10 @@ which incur interpreter overhead.
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# unique_justseen('AAAABBBCCDAABBB') --> A B C D A B
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# unique_justseen('ABBCcAD', str.lower) --> A B C A D
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return imap(next, imap(itemgetter(1), groupby(iterable, key)))
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Note, many of the above recipes can be optimized by replacing global lookups
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with local variables defined as default values. For example, the
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*dotproduct* recipe can be written as:
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def dotproduct(vec1, vec2, sum=sum, imap=imap, mul=operator.mul):
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return sum(imap(mul, vec1, vec2))
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