Arnaud Delobelle wrote:
Paul Rubin <http://phr...@nospam.invalid> writes:
Tim Chase <python.l...@tim.thechases.com> writes:
Return True if all elements of the iterable are
true. ...
Then I'd say the comment is misleading. An empty list has no item
that is true (or false), yet it returns true.
The comment is correct. "All the items of the iterable are true"
means EXACTLY the same thing as "there are no items of the iterable
that are false". The empty list has no false items. Therefore
all(empty_list) = True is the correct behavior.
Another possible implementation:
import operator,itertools
def all(xs):
return reduce(operator.and_, itertools.imap(bool, xs), True)
A contest! My entry:
def all(iterable):
return not sum(not x for x in iterable)
Problem with both entries: short-circuit evaluation.
def test_me(how_many=99999999999999999):
yield False
for _ in xrange(how_many): yield True
print all(test_me())
The stdlib version wisely bails on the first False. A
particularly useful aspect when test_me() does something
time-consuming:
def test_me(times=100)
for _ in xrange(times):
yield some_long_running_process_that_usually_returns_false()
where that process may do something like slurp a web-page across
the planet, or calculate some expensive expression.
-tkc
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