diff options
| -rw-r--r-- | Doc/library/itertools.rst | 29 | ||||
| -rw-r--r-- | Lib/test/test_itertools.py | 49 |
2 files changed, 77 insertions, 1 deletions
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst index fd77f99..254e055 100644 --- a/Doc/library/itertools.rst +++ b/Doc/library/itertools.rst @@ -837,6 +837,34 @@ which incur interpreter overhead. t1, t2 = tee(iterable) return filterfalse(pred, t1), filter(pred, t2) + def before_and_after(predicate, it): + """ Variant of takewhile() that allows complete + access to the remainder of the iterator. + + >>> all_upper, remainder = before_and_after(str.isupper, 'ABCdEfGhI') + >>> str.join('', all_upper) + 'ABC' + >>> str.join('', remainder) + 'dEfGhI' + + Note that the first iterator must be fully + consumed before the second iterator can + generate valid results. + """ + it = iter(it) + transition = [] + def true_iterator(): + for elem in it: + if predicate(elem): + yield elem + else: + transition.append(elem) + return + def remainder_iterator(): + yield from transition + yield from it + return true_iterator(), remainder_iterator() + def powerset(iterable): "powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)" s = list(iterable) @@ -948,4 +976,3 @@ which incur interpreter overhead. c, n = c*(n-r)//n, n-1 result.append(pool[-1-n]) return tuple(result) - diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py index 4019af0..0cf7eaf 100644 --- a/Lib/test/test_itertools.py +++ b/Lib/test/test_itertools.py @@ -2412,6 +2412,40 @@ Samuele ... pending -= 1 ... nexts = cycle(islice(nexts, pending)) +>>> def partition(pred, iterable): +... "Use a predicate to partition entries into false entries and true entries" +... # partition(is_odd, range(10)) --> 0 2 4 6 8 and 1 3 5 7 9 +... t1, t2 = tee(iterable) +... return filterfalse(pred, t1), filter(pred, t2) + +>>> def before_and_after(predicate, it): +... ''' Variant of takewhile() that allows complete +... access to the remainder of the iterator. +... +... >>> all_upper, remainder = before_and_after(str.isupper, 'ABCdEfGhI') +... >>> str.join('', all_upper) +... 'ABC' +... >>> str.join('', remainder) +... 'dEfGhI' +... +... Note that the first iterator must be fully +... consumed before the second iterator can +... generate valid results. +... ''' +... it = iter(it) +... transition = [] +... def true_iterator(): +... for elem in it: +... if predicate(elem): +... yield elem +... else: +... transition.append(elem) +... return +... def remainder_iterator(): +... yield from transition +... yield from it +... return true_iterator(), remainder_iterator() + >>> def powerset(iterable): ... "powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)" ... s = list(iterable) @@ -2539,6 +2573,21 @@ True >>> list(roundrobin('abc', 'd', 'ef')) ['a', 'd', 'e', 'b', 'f', 'c'] +>>> def is_odd(x): +... return x % 2 == 1 + +>>> evens, odds = partition(is_odd, range(10)) +>>> list(evens) +[0, 2, 4, 6, 8] +>>> list(odds) +[1, 3, 5, 7, 9] + +>>> all_upper, remainder = before_and_after(str.isupper, 'ABCdEfGhI') +>>> str.join('', all_upper) +'ABC' +>>> str.join('', remainder) +'dEfGhI' + >>> list(powerset([1,2,3])) [(), (1,), (2,), (3,), (1, 2), (1, 3), (2, 3), (1, 2, 3)] |