Rob Cowie a écrit : > I'm having a bit of trouble with this so any help would be gratefully > recieved... > > After splitting up a url I have a string of the form > 'tag1+tag2+tag3-tag4', or '-tag1-tag2' etc. The first tag will only be > preceeded by an operator if it is a '-', if it is preceded by nothing, > '+' is to be assumed. > > Using re.split, I can generate a list that looks thus: > ['tag1', '+', 'tag2', '+', 'tag3', '-', 'tag4'] > > I wish to derive two lists - each containing either tags to be > included, or tags to be excluded. My idea was to take an element, > examine what element precedes it and accordingly, insert it into the > relevant list. However, I have not been successful. > > Is there a better way that I have not considered?
If you're responsible for the original URL, you may consider rewriting it this way: scheme://domain.tld/resource?tag1=1&tag2=1&tag3=1&tag4=0 Else - and after you've finished cursing the guy that came out with such an innovative way to use url parameters - I think the first thing to do would be to fix the implicit-first-operator-mess, so you have something consistent: if the_list[0] != "-": the_list.insert(0, "+") Then a possible solution could be: todo = {'+' : [], '-' : []} for op, tag in zip(the_list[::2], the_list[1::2]): todo[op].append(tag) But there's surely something better... -- http://mail.python.org/mailman/listinfo/python-list