Efficiently change a key of a Python dict

Question

I'm looking to replace the keys of a dict to shorter variants so that it can be sent across the wire in a compact form. Is there a way to updating a key, rather than creating a new item in in the dict and deleting the old?

What I'm doing now:

>>> a = dict(long_key=None)
>>> a['l'] = a['long_key']
>>> del a['long_key']

What I would like to do is something like this:

>>> a = dict(long_key=None)
>>> a.update_key('long_key', 'l')

I'm unsure of dict's internals. However, it seems that something like update_key might be able to avoid needing to delete the old key.

Answer 1

A more elegant solution might be to create a new dictionary... essentially make a slightly different shallow copy:

a_send = dict((k[0], v) for k,v in a.items())

That will certainly be less space-efficient, though - are you looking for space efficiency, time efficiency, or code elegance?

Answer 2

That's premature optimization. If you really want to save bandwidth, do it by either compressing the data normally or use simpler data structures.

Answer 3

How many times do you need to send it? Maybe instead of changing anything, you can just process the keys as you go?

Instead of doing something like (guessing pseudo-code):

short_dict = shorten_keys(long_dict)
for k,v in short_dict:
    send_over(k,v)

do something like:

for k,v in long_dict:
    send_over(shorten(k),v)

If you have to send it many times, you can also create a map of long -> short keys and use it while sending. Wasting space / time to create copies might not be the best solution.