New submission from Peter Norvig <pnor...@google.com>:
PEP 289 says "the semantic definition of a list comprehension in Python 3.0
will be equivalent to list(<generator expression>). Here is a counterexample
where they differ (tested in 3.2):
def five(x):
"Generator yields the object x five times."
for _ in range(5):
yield x
# If we ask five() for 10 objects in a list comprehension,
# we get an error:
>>> F = five('x')
>>> [next(F) for _ in range(10)]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
StopIteration
# But if we ask five() for 10 objects in a list(generator expr),
# we get five objects, no error:
>>> F = five('x')
>>> list(next(F) for _ in range(10))
['x', 'x', 'x', 'x', 'x']
----------
components: None
messages: 161023
nosy: Peter.Norvig
priority: normal
severity: normal
status: open
title: list(<generator expression>) != [<list comprehension>]
type: behavior
versions: Python 3.2
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue14845>
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