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Re: Understanding Python Code

References <4045d8ca-923d-4384-a684-57cbd80ab7b7@googlegroups.com> <mailman.11118.1403118997.18130.python-list@python.org> <03a82bc4-340f-4b16-8dbb-791b706c7862@googlegroups.com> <mailman.11131.1403161255.18130.python-list@python.org> <f1d47c99-b309-4ecd-8a6b-1f3b25d83370@googlegroups.com>
From Ian Kelly <ian.g.kelly@gmail.com>
Date 2014-06-19 08:09 -0600
Subject Re: Understanding Python Code
Newsgroups comp.lang.python
Message-ID <mailman.11152.1403187031.18130.python-list@python.org> (permalink)

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On Thu, Jun 19, 2014 at 3:48 AM,  <subhabangalore@gmail.com> wrote:
> I am trying to see this line,
> prev_f_sum = sum(f_prev[k]*a[k][st] for k in states)
>
> a[k][st], and f_prev[k] I could take out and understood.
> Now as it is doing sum() so it must be over a list,
> I am trying to understand the number of entities in the list, thinking whether to put len(), and see for which entities it is doing the sum.

It's summing a generator expression, not a list.  If it helps to
understand it, you could rewrite that line like this:

values_to_be_summed = []
for k in states:
    values_to_be_summed.append(f_prev[k]*a[k][st])
prev_f_sum = sum(values_to_be_summed)

So the number of entities in the list is len(states).

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Thread

Understanding Python Code subhabangalore@gmail.com - 2014-06-18 09:36 -0700
  Re: Understanding Python Code Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-18 13:15 -0600
    Re: Understanding Python Code subhabangalore@gmail.com - 2014-06-18 22:50 -0700
      Re: Understanding Python Code Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-19 01:00 -0600
        Re: Understanding Python Code subhabangalore@gmail.com - 2014-06-19 02:48 -0700
          Re: Understanding Python Code Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-19 08:09 -0600
            Re: Understanding Python Code subhabangalore@gmail.com - 2014-06-19 07:27 -0700
              Re: Understanding Python Code subhabangalore@gmail.com - 2014-06-19 11:44 -0700
                Re: Understanding Python Code Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-19 13:07 -0600
                Understanding Python Code[Forward_Backward_Wikipedia] subhabangalore@gmail.com - 2014-06-21 15:05 -0700

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