Stephen Drake added the comment:
Ok, I can accept that. I think my mistake was to assume that because a
generator has a close() method, I could treat it as a lightweight wrapper for
another closeable object.
But it's better to regard a generator function that wraps an iterable as
something more akin to map() or filter(), and use a class if it's necessary to
wrap a file such that close() is passed through.
I happened to take a fresh look at this just the other day and it also occurred
to me that the kind of composition I was trying to do can work if it's
generators all the way down:
def open_lines(name, mode='rt', buffering=-1):
with open(name, mode, buffering) as f:
for line in f:
yield line
def logged_lines(f):
try:
for line in f:
logging.warning(line.strip())
yield line
finally:
f.close()
lines = open_lines('yyy', 'r')
if verbose:
lines = logged_lines(lines)
try:
for line in lines:
print(line)
finally:
lines.close()
So a generator can transparently wrap a plain iterable or another generator,
but not closeable objects in general. There's nothing really wrong with that,
so I'm happy for this issue to be closed as invalid.
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<http://bugs.python.org/issue23227>
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