Gerard Flanagan wrote: > Rob Cowie wrote: > >>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 this method is >>suitable, how might I implement it? >> >>Thanks all, >> >>Rob Cowie > > > a = [ '+', 'tag1', '+', 'tag2', '-', 'tag3', '+', 'tag4' ] > > import itertools > > b = list(itertools.islice(a,0,8,2)) > c = list(itertools.islice(a,1,8,2)) > > result1 = [x[1] for x in itertools.izip(b,c) if x[0] == '+'] > result2 = [x[1] for x in itertools.izip(b,c) if x[0] == '-'] > > print > print result1 > print result2 > > > Gerard >
Unfortunately this does not address the complete specification: >>> a = [ 'tag1', '+', 'tag2', '-', 'tag3', '+', 'tag4' ] >>> >>> import itertools >>> >>> b = list(itertools.islice(a,0,len(a),2)) >>> c = list(itertools.islice(a,1,len(a),2)) >>> >>> result1 = [x[1] for x in itertools.izip(b,c) if x[0] == '+'] >>> result2 = [x[1] for x in itertools.izip(b,c) if x[0] == '-'] >>> >>> print >>> print result1 [] >>> print result2 [] Need to check for the absence of that first op. James -- http://mail.python.org/mailman/listinfo/python-list
