building a dict

[rurpy at yahoo.com]

On Mar 13, 8:28 am, Patrick Maupin <pmau... at gmail.com> wrote:
> On Mar 13, 9:05 am, vsoler <vicente.so... at gmail.com> wrote:
>
> > Say that "m" is a tuple of 2-tuples
>
> > m=(('as',3), ('ab',5), (None, 1), ('as',None), ('as',6))
>
> > and I need to build a "d" dict where each key has an associated list
> > whose first element is the count, and the second is the sum. If a 2-
> > tuple contains a None value, it should be discarded.
>
> > The expected result is:
> > d={'as':[2, 9], 'ab': [1,5]}
>
> > How should I proceed? So far I have been unsuccessful. I have tried
> > with a "for" loop.
>
> Post your first try at a for loop, and people might be willing to
> point out problems, but this is such a basic for loop that it is
> unlikely that anybody is going to write your ENTIRE homework for you.

This is probably what you (OP) were trying to come up with?
[untested]

d = {}
for item in m:
    key = m[0];  value = m[1]
    if key is None or value is None: continue
    if key not in dict:
        d[key] = [value]
    else:
        d[key].append (value)

You can replace the
  for item in m:
      key = m[0];  value = m[1]
above with
  for key, value in m:
which is a little nicer.

However, as other responses point out, when you want
to "accumulate" results in a dict, collections.defaultdict
should pop into your mind first.