On Jul 11, 1:30 pm, Nick Craig-Wood <[EMAIL PROTECTED]> wrote: > Alan Isaac <[EMAIL PROTECTED]> wrote: > > Miles wrote: > > > What boolean operation does '-' represent? > > > Complementation. > > And as usual, a-b is to be interpreted as a+(-b). > > In which case the desired behavior is > > False-True = False+(-True)=False+False = False > > If you want to do algebra with bools in python then use the logical > operators (and or not) and not the arithmetical operators. > > Eg > > >>> False or not True > False
Let me comment on what I suspect is Alan's Hidden Agenda (tm). Since this question surfaced earlier on the numpy list, I suspect that part of the motivation here has to do with trying to come up with a natural way to work with arrays of booleans. The operators and,or,not don't work for this purpose since they can't be overloaded to return an arbitrary value. You can almost make this work with &,|,^: >>> a = np.array([True, False, False]) >>> b = np.array([True, True, False]) >>> a & b array([ True, False, False], dtype=bool) >>> a | b array([ True, True, False], dtype=bool) >>> a ^ b array([False, True, False], dtype=bool) This is meshes well with the behavior of True and False: >>> True & True True >>> True | True True >>> True ^ True False This doesn't leave you with anything equivalent to 'not' however. Or nothing consistent. Currently '~a' will complement a boolean array,: >>> ~a array([False, True, True], dtype=bool) However that's less than ideal since it doesn't mesh up with the behavior of booleans on their own: >>> ~True -2 That's potentially confusing. It's not any skin of my nose since I use, and will likely continue to use, boolean arrays in only the most rudimentary ways. However, I thought I'd offer some additional context. -tim -- http://mail.python.org/mailman/listinfo/python-list
