[Tutor] quickie: a better dynamic dictionary update?

[Terry Carroll]

On Tue, 11 Jul 2006, Terry Carroll wrote:

> On Tue, 11 Jul 2006, Marcus Goldfish wrote:
> 
> > # 1st, find the 'stale' items in our dictionary to delete
> > # lstKeepers is a list of current pictures
> > # Note: if I try to iterate over the keys of the dict and
> > # remove-as-I-go, I get an exception (dict size changed
> > # during iteration)
> > lstRemove = []
> > for key in myDict:
> >    if key not in lstKeepers:
> >        lstRemove.append(key)
> > 
> > # 2nd, remove them
> > for oldKey in lstRemove:
> >    del myDict[oldKey]
> 
> [snip code]
> It's still a two-passer, but I don't see straightforward any way around
> that, if you want to update the dictionary (as opposed to making a new
> dictionary with the result, which could probably be done with an
> excessively clever list comprehension).

Actually, it turns out not to be excessively clever at all (if I could do
it):

myDict = dict([(key, myDict[key]) for key in myDict.keys()
               if key in lstKeepers])

I'm not sure it's any nicer looking, though, than my first suggestion 
(although my first suggestion is probably a little slower).