[EMAIL PROTECTED] wrote: > Bryan Olson wrote: >> How can we efficiently implement an abstract data type, call it >> 'DoubleDict', where the state of a DoubleDict is a binary >> relation, that is, a set of pairs (x, y); and the operations on >> a DoubleDict are those on a Python set, plus: >> >> find_by_first(self, x): return [y where (x, y) in DoubleDict] >> >> find_by_second(self, y): return [x where (x, y) in DoubleDict]
> It gets hairier if you have an element that isn't a first or second > necessarily. > > find_by_other(self, x): return [y where (x, y) in DoubleDict or > (y, x) in DoubleDict] Do you need all three find_by's, or are the pairs actually unordered, so you just need to find partners? Are the relations many-to-many, and if so do you want duplicates removed? As programming exercises, the variants are all reasonable and possibly interesting. I was just trying to answer the call to nail down the problem statement. -- --Bryan -- http://mail.python.org/mailman/listinfo/python-list
