Extract subset of key-value pairs from dictionary?

You could try:

dict((k, bigdict[k]) for k in ('l', 'm', 'n'))

... or in Python versions 2.7 or later:

{k: bigdict[k] for k in ('l', 'm', 'n')}

I'm assuming that you know the keys are going to be in the dictionary. See the answer by Håvard S if you don't.

Alternatively, as timbo points out in the comments, if you want a key that's missing in bigdict to map to None, you can do:

{k: bigdict.get(k, None) for k in ('l', 'm', 'n')}

If you're using Python 3, and you only want keys in the new dict that actually exist in the original one, you can use the fact to view objects implement some set operations:

{k: bigdict[k] for k in bigdict.keys() & {'l', 'm', 'n'}}

A bit shorter, at least:

wanted_keys = ['l', 'm', 'n'] # The keys you want
dict((k, bigdict[k]) for k in wanted_keys if k in bigdict)

interesting_keys = ('l', 'm', 'n')
subdict = {x: bigdict[x] for x in interesting_keys if x in bigdict}

This answer uses a dictionary comprehension similar to the selected answer, but will not except on a missing item.

python 2 version:

{k:v for k, v in bigDict.iteritems() if k in ('l', 'm', 'n')}

python 3 version:

{k:v for k, v in bigDict.items() if k in ('l', 'm', 'n')}