[Python-3000] have zip() raise exception for sequences of different lengths (original) (raw)
Steven Bethard steven.bethard at gmail.com
Thu Aug 31 01:33:27 CEST 2006
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On 8/30/06, Raymond Hettinger <rhettinger at ewtllc.com> wrote:
Until now, there have been zero requests for zip() to have exception raising behavior.
For Python 3k, I recommend: * simply replacing zip() with itertools.izip() * keeping the ziplongest() in a separate module * punting on an exception raising version The first covers 99% of use cases.
I guess it depends what you mean by "covers". If you mean "produces the correct output for correct input" then yes, it does, but so would the exception raising one. I contend that it often does the wrong thing for incorrect input by silently truncating. To try to give a fair evaluation of this contention, I looked at some stdlib examples and tried to classify them:
Examples where different lengths should be an error:
compiler/pycodegen.py: for i, for_ in zip(range(len(node.quals)), node.quals): dis.py: for byte_incr, line_incr in zip(byte_increments, line_increments): email/Header.py: return zip(chunks, [charset]*len(chunks)) filecmp.py: a = dict(izip(imap(os.path.normcase, self.left_list), self.left_list)) idlelib/keybindingDialog.py: for modifier, variable in zip(self.modifiers, self.modifier_vars):
Examples where truncation is needed:
csv.py: d = dict(zip(self.fieldnames, row)) idlelib/EditorWindow.py: for i, file in zip(count(), rf_list):
A couple of the examples (pycodegen.py, EditorWindow.py) are really just performing a poor-man's enumerate(), but with a cursory glance it still looks to me like there are more cases in the stdlib where it is a programming error to have lists of different sizes.
If changing zip()'s behavior to match the most common use case is totally out, the stdlib code at least argues for adding something like itertools.izip_exact().
Steve
I'm not in-sane. Indeed, I am so far out of sane that you appear a tiny blip on the distant coast of sanity. --- Bucky Katt, Get Fuzzy
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