Gerard Flanagan <[EMAIL PROTECTED]> wrote:
...
> a = [ '+', 'tag1', '+', 'tag2', '-', 'tag3', '+', 'tag4' ]
>
> import itertools
>
> b = list(itertools.islice(a,0,8,2))
> c = list(itertools.islice(a,1,8,2))
Much as I love itertools, this specific task would be best expressed ad
b = a[::2]
c = a[1::2]
Do note that you really don't need the 'list(...)' here, for the
following use:
> 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] == '-']
...would be just as good if b and c were islice objects rather than
lists, except for the issue of _repeating_ (izipping twice). I'd rather
do some variant of a single-loop such as:
results = {'+':[], '-':[]}
for operator, tag in itertools.izip(a[::2], a[1::2]):
results[operator].append(tag)
and use results['+'] and results['-'] thereafter.
These approaches do not consider the inconvenient fact that the leading
'+' does in fact not appear in list a -- it needs to be assumed, the OP
stated; only a '-' would instead appear explicitly. Little for it but
specialcasing depending on whether a[0]=='-', I think -- e.g. in the
above 3-line snippet of mine, insert right after the first line:
if a[0]!='-': results['+'].append(a.pop(0))
Alex
--
http://mail.python.org/mailman/listinfo/python-list
