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Add another example of PEP 479 justification, courtesy of Isaac Schwabacher

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Chris Angelico 2014-12-07 02:45:03 +11:00
parent d6edada20d
commit a09e8b3dae
1 changed files with 16 additions and 3 deletions
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19
pep-0479.txt
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@ -72,9 +72,9 @@ stumble on these cases by accident::
print('commit') print('commit')
def do_it(): def do_it():
print('Refactored preparations') print('Refactored initial setup')
yield # Body of with-statement is executed here yield # Body of with-statement is executed here
print('Refactored finalization') print('Refactored finalization of successful transaction')
def gene(): def gene():
for i in range(2): for i in range(2):
@ -92,7 +92,20 @@ subtle bug: if the wrapped block raises ``StopIteration``, under the
current behavior this exception will be swallowed by the context current behavior this exception will be swallowed by the context
manager; and, worse, the finalization is silently skipped! Similarly manager; and, worse, the finalization is silently skipped! Similarly
problematic behavior occurs when an ``asyncio`` coroutine raises problematic behavior occurs when an ``asyncio`` coroutine raises
``StopIteration``, causing it to terminate silently. ``StopIteration``, causing it to terminate silently, or when ``next``
is used to take the first result from an iterator that unexpectedly
turns out to be empty, for example::
# using the same context manager as above
import pathlib
with transaction():
print('commit file {}'.format(
# I can never remember what the README extension is
next(pathlib.Path('/some/dir').glob('README*'))))
In both cases, the refactoring abstraction of ``yield from`` breaks
in the presence of bugs in client code.
Additionally, the proposal reduces the difference between list Additionally, the proposal reduces the difference between list
comprehensions and generator expressions, preventing surprises such as comprehensions and generator expressions, preventing surprises such as