pyhton list – remove dictionares with certain key

Question

When running this python code:

shapes = [{"label": "bad_stuff"}, {"label": "cat"}, {"label": "cat"},{"label": "cat"}, {"label": "bad_stuff"}, {"label": "bad_stuff"}]
for elem in shapes:
    if elem['label'] == "bad_stuff":
        shapes.remove(elem)

… I get this result:

[{'label': 'cat'}, {'label': 'cat'}, {'label': 'cat'}, {'label': 'bad_stuff'}]

Why does not the code remove the last element in the list and how can I solve it?

Asked By: Johan hvn

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Source

Answer 1

Because you are modifying list during for loop.
Let’s see what’s happening in your code:

On 1st interation it removes shapes[0] item.
2, 3, 4 iterations do not satisfy condition, so passed.
On 5th iteration the elem is {"label": "bad_stuff"}, and your shapes looks like this:

[{"label": "cat"}, {"label": "cat"},{"label": "cat"}, **{"label": "bad_stuff"}**, {"label": "bad_stuff"}]

So when you remove(elem) on this step, it removes last item in the list.
And since you removed last item – iteation stops.

There is solution to your problem:

shapes = [{"label": "bad_stuff"}, {"label": "cat"}, {"label": "cat"},{"label": "cat"}, {"label": "bad_stuff"}, {"label": "bad_stuff"}]

cat_shapes = []
for elem in shapes:
    if elem['label'] != "bad_stuff":
        cat_shapes.append(elem)

Another solution mentioned in comments by DanielB
:

cat_shapes = [elem for elem in shapes if elem['label'] != "bad_stuff"]

Answered By: Nick Laid

Answer 2

You can do this with filter,

list(filter(lambda x:x['label'] != 'bad_stuff', shapes))
# [{'label': 'cat'}, {'label': 'cat'}, {'label': 'cat'}]

Answered By: Rahul K P

Answer 3

If you want to remove matching elements from list please check below code

def remove_bad_stuff(shapes, remove_value):
    for elem in shapes:
        if elem['label'] == remove_value:
            shapes.remove(elem)
            remove_bad_stuff(shapes, remove_value)

shapes = [{"label": "bad_stuff"}, {"label": "cat"}, {"label": "cat"},{"label": "cat"}, {"label": "bad_stuff"}, {"label": "bad_stuff"}]
remove_bad_stuff(shapes,"bad_stuff")
print(shapes)

Answered By: Neo-coder

pyhton list – remove dictionares with certain key

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