"Volker Grabsch" <[EMAIL PROTECTED]> schrieb im Newsbeitrag news:[EMAIL PROTECTED] | Hello! | | Ich just found a very nice 'pythonic' solution for an often appearing | problem. I didn't find it documented anywhere, so I'm posting it here. | If this isn't new in any way, I'd really like to get to know it. | | Example problem: | I have some "datetime" objects and want to sort them, as here: | | birthdays = [d1,d2,d3,d4] | birthdays.sort() | | However, I don't want to sort them the default way. These are birthdays, | so only the month and day do matter, not the year. E.g.: | | 2003-01-01 should be smaller than 1984-05-01 | | So I have to write the comparison on my own, e.g. | | def cmp_birthdays(d1,d2): | if d1.month > d2.month: return 1 | if d1.month < d2.month: return -1 | if d1.day > d2.day: return 1 | if d1.day < d2.day: return -1 | return 0 | | ... | birthdays.sort(cmp_birthdays)
If you don't care about the year, why not just "normalize" the year to all be the same using the replace method of the date instance? Something like: d1 = datetime.date(2004, 12, 2) d2 = datetime.date(2001, 12, 3) d3 = datetime.date(2002, 12, 6) d4 = datetime.date(1977, 12, 7) dates =[d1,d2,d3,d4] datesNorm = [obj.replace(year=1900) for obj in (dates)] datesNorm.sort() print datesNorm # etcetera HTH, --- Vincent | | This implementation of cmp_birthdays is very ugly. Image you want to | chain more than 2 values in that "cmp_birthdays". I also want to use the | builtin "cmp" function, not ">" and "<". | | After thinking some minutes about it, I found a very nice solution: | I have some "cmp"s one aftter another. If one if them return 1 oder -1, | it sould be returned. If it returns 0, the next "cmp" is used. In other | words: I have a sequence of numbers, and want to get the first one that | is not 0. (or return 0, if all numbers were 0) | | But this is exactly what the "or" operator does, due to short-circuit | evaluation. In this example, that means: | | def cmp_bithdays(d1,d2): | return cmp(d1.month,d2.month) or cmp(d1.day,d2.day) | | The generic pattern is: | | return cmp(...) or cmp (...) or cmp(...) or ... | | I'm not sure whether this pattern is already a "common recipe", but | I found it to be a very nice idea. :-) | | Any opinions? | | | Greets, | | Volker | | -- | Volker Grabsch | ---<<(())>>--- | \frac{\left|\vartheta_0\times\{\ell,\kappa\in\Re\}\right|}{\sqrt | [G]{-\Gamma(\alpha)\cdot\mathcal{B}^{\left[\oint\!c_\hbar\right]}}} -- http://mail.python.org/mailman/listinfo/python-list