Removing keys from dictionary in Python

Question

I want to remove some keys from a Python dictionary. The keys are provided in a list; my code so far:

my_keys = [2,4]
my_dict = {1:"aaaa" , 2: "bbb", 3:"ccc", 4:"ddd" }

for number in my_keys:
    for key, value in my_dict.items():
            if key == number:
                del my_dict[(key)]

@njzk2 presumably because the key may or may not be in the dictionary. — ffledgling, Feb 28 '16 at 00:01

ffledgling · Accepted Answer · 2016-02-27T23:50:55.107

4

You can use a dict comprehension, like so:

{x:y for x,y in my_dict.items() if x not in my_keys}

As e0k and njzk2 have suggested in the comments, if you're happy to modify the existing dictionary, the following works better:

for key in my_keys:
    try:
        del my_dict[key]
    except KeyError:
        pass # Key wasn't in the dictionary at all.

edited Feb 27 '16 at 23:50

answered Feb 27 '16 at 23:45

ffledgling

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Modifying the existing `dict` might be more efficient than creating a new one. – e0k Feb 27 '16 at 23:48
@e0k definitely, that was already suggested by njzk2 in his comment, I'll add it in anyway. – ffledgling Feb 27 '16 at 23:49

score 2 · Answer 2 · answered Feb 27 '16 at 23:52

Here's how you do it in place:

>>> my_keys = [2,4]
>>> my_dict = {1:"aaaa" , 2: "bbb", 3:"ccc", 4:"ddd" }
>>> for key in my_keys:
...     del my_dict[key]
... 
>>> my_dict
{1: 'aaaa', 3: 'ccc'}

As a sidenote: To delete a key and get the value, use dict.pop

>>> x = my_dict.pop(1)
>>> x
'aaaa'
>>> my_dict
{3: 'ccc'}

score 2 · Answer 3 · edited Oct 27 '16 at 12:18

2

You could use a range with a step of 2, and then delete each key for each value in the range. You can also use map, which is a great function.

map(my_dict.pop, [2,4])

And if you want to catch an error where the key isn't in the dictionary, use a lambda function thus:

map(lambda x: my_dict.pop(x, None), [2,4])

edited Oct 27 '16 at 12:18

Tom Fuller

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answered Feb 27 '16 at 23:59

opeonikute

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Removing keys from dictionary in Python

3 Answers3