On Wed, Apr 24, 2013 at 1:40 AM, Roy Smith <r...@panix.com> 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?
The definition of the for loop is sufficiently simple that this is safe, with the caveat already mentioned (that __iter__ is just returning self). And calling next() inside the loop will simply terminate the loop if there's nothing there, so I'd not have a problem with code like that - for instance, if I wanted to iterate over pairs of lines, I'd happily do this: for line1 in f: line2=next(f) print(line2) print(line1) That'll happily swap pairs, ignoring any stray line at the end of the file. Why bother catching StopIteration just to break? ChrisA -- http://mail.python.org/mailman/listinfo/python-list
