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Date: Sun, 8 Dec 2013 12:58:20 -0600
From: Tim Chase <python.list@tim.thechases.com>
To: python-list@python.org
Subject: Re: Eliminate "extra" variable
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Xref: csiph.com comp.lang.python:61313

On 2013-12-08 15:04, Peter Otten wrote:
> >     data = dict(
> >       (str(date), {source: freq})
> >       for date, freq, source in original_data
> >       )  
> 
> or even just
> 
> data = {str(date): {source: freq}
>         for date, freq, source in original_data}

I maintain enough pre-2.7 code that I tend to eschew
dict-comprehensions for the time being.  I like them as a language
addition, but can't use them yet in most of the code-bases with which
I work.  To the OP, if you don't have to support pre-2.7 code, then
this is a tidier way to go.

> But do you really need a dict with a single key? And is it even
> correct? If a date occurs twice only the last source:freq pair is
> kept. Without knowing the context the humble
> 
> data = {}
> for date, freq, source in original_data:
>     source_to_freq = data.setdefault(date, {})
>     if source in source_to_freq:
>         raise ValueError(
>             "Multiple frequencies for one source not supported")
>     source_to_freq[source] = freq
> 
> appears so much more plausible...

The OP's code didn't do any such sanity-checking so I made the
assumption that the data came in clean.  I know better than to trust
incoming data (even my own) in my own code, but...

(followup to the OP's reply elsewhere in the thread coming shortly)

-tkc