[dictionary] how to get key by item

[Roy Smith]

Skip Montanaro <skip at pobox.com> wrote:

>     Roy> BTW, does Python really build the intermediate list and throw it
>     Roy> away after using it to initialize the dictionary, or is it smart
>     Roy> enough to know that it doesn't really need to build the whole list
>     Roy> in memory?
> 
> That's why I called .iteritems() in my example.  It won't generate the
> entire list of tuples as .items() would.

I know it won't generate the list of items from the forward dict, but I 
was thinking of the list generated by the list comprehension, passed as 
the argument to the reverse dict constructor.  That's the throw-away 
list I was thinking of (see Tim Delaney's response to my post).