delete all keys except one in dictionary

python dictionary unset
NIlesh Sharma picture NIlesh Sharma · Sep 12, 2012 · Viewed 17.2k times · Source

I have a dictionary 

lang = {'ar':'arabic', 'ur':'urdu','en':'english'}

What I want to do is to delete all the keys except one key. Suppose I want to save only en here. How can I do it ? (pythonic solution)
What I have tried:

In [18]: for k in lang:
   ....:     if k != 'en':
   ....:         del lang_name[k]
   ....

Which gave me the run time error:RuntimeError: dictionary changed size during iteration

Answer

Fabian picture Fabian · Sep 12, 2012

Why don't you just create a new one?

lang = {'en': lang['en']}

Edit: Benchmark between mine and jimifiki's solution:

$ python -m timeit "lang = {'ar':'arabic', 'ur':'urdu','en':'english'}; en_value = lang['en']; lang.clear(); lang['en'] = en_value"
1000000 loops, best of 3: 0.369 usec per loop

$ python -m timeit "lang = {'ar':'arabic', 'ur':'urdu','en':'english'}; lang = {'en': lang['en']}"
1000000 loops, best of 3: 0.319 usec per loop

Edit 2: jimifiki's pointed out in the comments that my solution keeps the original object unchanged.

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