CODEWITHSUNDEEP
pythondictionaryunset
NIlesh Sharma
NIlesh Sharma

Reputation: 5665

delete all keys except one in dictionary

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

Upvotes: 40

Views: 33700

Answers (4)

nehem
nehem

Reputation: 13662

pop() it via for loop like this

[s.pop(k) for k in list(s.keys()) if k != 'en']

Upvotes: 8

Fabian
Fabian

Reputation: 4348

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.

Upvotes: 50

jimifiki
jimifiki

Reputation: 5544

This is quite fast: 

En_Value = lang['en']
lang.clear() 
lang['en'] = En_Value

Upvotes: 36

thegrinner
thegrinner

Reputation: 12241

Iterate over keys() instead:

for k in lang.keys():
    if k != 'en':
        del lang_name[k]

If you're using Python 3 I believe you need to use list(lang.keys()) instead.

Upvotes: 11

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