79 lines
1.7 KiB
Python
79 lines
1.7 KiB
Python
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## -*- coding: utf-8 -*-
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"""
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first
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=====
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first is the function you always missed in Python.
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In the simplest case, it returns the first true element from an iterable:
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>>> from first import first
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>>> first([0, False, None, [], (), 42])
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42
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Or None if there is none:
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>>> from first import first
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>>> first([]) is None
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True
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>>> first([0, False, None, [], ()]) is None
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True
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It also supports the passing of a key argument to help selecting the first
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match in a more advanced way.
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>>> from first import first
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>>> first([1, 1, 3, 4, 5], key=lambda x: x % 2 == 0)
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4
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:copyright: (c) 2012 by Hynek Schlawack.
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:license: MIT, see LICENSE for more details.
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"""
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__title__ = 'first'
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__version__ = '2.0.2'
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__author__ = 'Hynek Schlawack'
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__license__ = 'MIT'
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__copyright__ = 'Copyright 2012 Hynek Schlawack'
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def first(iterable, default=None, key=None):
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"""
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Return first element of `iterable` that evaluates true, else return None
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(or an optional default value).
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>>> first([0, False, None, [], (), 42])
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42
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>>> first([0, False, None, [], ()]) is None
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True
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>>> first([0, False, None, [], ()], default='ohai')
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'ohai'
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>>> import re
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>>> m = first(re.match(regex, 'abc') for regex in ['b.*', 'a(.*)'])
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>>> m.group(1)
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'bc'
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The optional `key` argument specifies a one-argument predicate function
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like that used for `filter()`. The `key` argument, if supplied, must be
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in keyword form. For example:
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>>> first([1, 1, 3, 4, 5], key=lambda x: x % 2 == 0)
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4
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"""
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if key is None:
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for el in iterable:
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if el:
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return el
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else:
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for el in iterable:
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if key(el):
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return el
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return default
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