[Python-ideas] use context managers for new-style "for" statement
dangyogi at gmail.com
Fri Feb 20 23:41:33 CET 2009
An idea occurred to me about another way to achieve "new-style" for
statements that finalize generators properly:
1. Modify for statements to accept context mangers in addition to
iterables. If it gets a context manager, it calls __exit__ when the
loop terminates for any reason. Otherwise, it does what it does now.
2. Add an optional __throw__ method to context managers. If the
context manager has a __throw__ method, the for statement forwards
uncaught exceptions within its body to the context manager.
Thus, you can use:
for i in closing(gen(x)):
if you want the generator closed automatically.
This would also work for files:
for line in open(filename):
We might also add a new context manager to contextlib to do both the
close and the throw. Maybe call it throwing_to?
for i in throwing_to(gen(x)):
I would think that throwing_to would also do what closing does.
This somewhat simplifies the common "with closing"/"for" pattern as well
as adds support for the new close/throw generator methods without any
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