On Tue, May 3, 2016 at 8:00 PM, <pavlovevide...@gmail.com> wrote: > > What you should have been expecting is a symmetry. Say you have a string G. > islower(G) will return a certain result. Now take every letter in G and swap > the case, and call that string g. isupper(g) will always return the same > result is islower(G). > > More succinctly, for any string x, the following is always ture: > > islower(x) == isupper(swapcase(x)) > > But that is not the same thing, and does not imply, as the following identity > (which it turns out is not always true, as we've seen): > > islower(x) == not isupper(x) > > > Another example of functions that behave like this are ispositive and > isnegative. The identity "ispositive(x) == isnegative(-x)" is always true. > However, "ispositive(x) == not isnegative(x)" is false if x == 0. >
This assumes, of course, that there is a function swapcase which can return a string with case inverted. I'm not sure such a function exists. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
