On 9/17/07, Nick Alexander <[EMAIL PROTECTED]> wrote: > > > > Robert, Since you do so much work on Cython, maybe you could think > > about the formal specification of the Python language and see whether > > .. > > not appearing in a string is ever valid Python. I.e., could we add > > [expr1 .. expr2] > > to the language without running into problems? > > Much like generators (K.<x>), this cannot be added to the preparser > without parsing arbitary python expressions (expr1 and expr2 in this > case). At the moment, you can make the preparser barf and it would > be a great deal of work to fix. Are we willing to do another > "correct 90% of the time" hack? If this is considered very valuable, > I suggest we hijack a Python binary operator and repurpose it. Or we > could uniformly preparse '..' to be that redefined operator; that > would be better. > > I vote against.
Just for clarification, could you explain why the following algorithm wouldn't suffice to parse the above 100% of the time? Suppose at position i, i+1 in the input string that there is "..", and this is not in a string. Reduce i counting ['s and ]'s that are not in a string literal until the count of [ is greater than the count of ]. This locates the left [. Starting again with position i at .., increase i counting ['s and ]'s not in string literals until the count of ] is greater than the count of ['s. I naively think the above should correctly find the positions of [ and ], and hence of expr1 and expr2, in [ expr1 ... expr2 ] in all cases. I naively think this because I think that any valid Python expression with a [ must have a balanced ] (discarding string literals). -- William --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://sage.scipy.org/sage/ and http://modular.math.washington.edu/sage/ -~----------~----~----~----~------~----~------~--~---
