Roy Smith wrote:
> In reviewing somebody else's code today, I found the following
> construct (eliding some details):
>
> f = open(filename)
> for line in f:
> if re.search(pattern1, line):
> outer_line = f.next()
> for inner_line in f:
> if re.search(pattern2, inner_line):
> inner_line = f.next()
>
> Somewhat to my surprise, the code worked. I didn't know it was legal
> to do nested iterations over the same iterable (not to mention mixing
> calls to next() with for-loops). Is this guaranteed to work in all
> situations?
That depends on what you mean by "all". A well-behaved iterator like
Python's file object allows mixing of for loops and next(...) calls, but
stupid people who deserve to burn in hell sometimes do
class MyIterable:
def __iter__(self):
reset_internal_counter()
return self
with the consequence that every for loop implicitly resets the iterator's
state.
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