Remove a dictionary key that has a certain value

Question

I know dictionary's are not meant to be used this way, so there is no built in function to help do this, but I need to delete every entry in my dictionary that has a specific value.

so if my dictionary looks like:

'NameofEntry1': '0'
'NameofEntry2': 'DNC'
 ...

I need to delete(probably pop) all the entries that have value DNC, there are multiple in the dictionary.

score 23 · Accepted Answer · edited Dec 09 '19 at 09:44

23

Modifying the original dict:

for k,v in your_dict.items():
    if v == 'DNC':
       del your_dict[k]

or create a new dict using dict comprehension:

your_dict = {k:v for k,v in your_dict.items() if v != 'DNC'}

From the docs on iteritems(),iterkeys() and itervalues():

Using iteritems(), iterkeys() or itervalues() while adding or deleting entries in the dictionary may raise a RuntimeError or fail to iterate over all entries.

Same applies to the normal for key in dict: loop.

In Python 3 this is applicable to dict.keys(), dict.values() and dict.items().

edited Dec 09 '19 at 09:44

ChrisF

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answered Jun 13 '13 at 19:15

Ashwini Chaudhary

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1

I get `RuntimeError: dictionary changed size during iteration` – Climbs_lika_Spyder Jun 30 '20 at 18:40
@Climbs_lika_Spyder Check the statement about Python 3 in last line. – Ashwini Chaudhary Jun 30 '20 at 20:59
In Python 3, you need `list(d.items())` as mentioned in @jared's answer. – Climbs_lika_Spyder Jul 01 '20 at 16:13

score 8 · Answer 2 · answered Jun 13 '13 at 19:16

You just need to make sure that you aren't modifying the dictionary while you are iterating over it else you would get RuntimeError: dictionary changed size during iteration.

So you need to iterate over a copy of the keys, values (for d use d.items() in 2.x or list(d.items()) in 3.x)

>>> d = {'NameofEntry1': '0', 'NameofEntry2': 'DNC'}
>>> for k,v in d.items():
...     if v == 'DNC':
...         del d[k]
... 
>>> d
{'NameofEntry1': '0'}

score 2 · Answer 3 · edited Jun 13 '13 at 19:44

2

This should work:

for key, value in dic.items():
     if value == 'DNC':
         dic.pop(key)

edited Jun 13 '13 at 19:44

Ashwini Chaudhary

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answered Jun 13 '13 at 19:16

Ankur Ankan

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score 0 · Answer 4 · answered Jun 13 '13 at 20:22

If restrictions re: modifying the dictionary while iterating on it is a problem, you could create a new class compatible with dict that stores a reverse index of all keys that have the given value (updated at create / update / delete of dict item), which can be arguments to del without iterating over the dict's items.

Subclass dict, and override __setitem__, __delitem__, pop, popitem and clear.

If this is an operation you're doing a lot of, that might be convenient and fast.

Remove a dictionary key that has a certain value

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