CODEWITHSUNDEEP
pythonmethodsdictionary
Xeos
Xeos

Reputation: 6497

Remove key from dictionary in Python returning new dictionary

I have a dictionary

d = {'a':1, 'b':2, 'c':3}

I need to remove a key, say c and return the dictionary without that key in one function call

{'a':1, 'b':2}

d.pop('c') will return the key value - 3 - instead of the dictionary.

I am going to need one function solution if it exists, as this will go into comprehensions

Upvotes: 99

Views: 79355

Answers (9)

govind
govind

Reputation: 250

Probably not exactly what you're looking for, but here's a fun one that (ab)uses the maligned walrus operator:

>>> x = {"a": "a", "b": "b"}
>>> (x_without_a := dict(x)).pop("a")
'a'
>>> x
{'a': 'a', 'b': 'b'}
>>> x_without_a
{'b': 'b'}

Upvotes: 1

Chris Flesher
Chris Flesher

Reputation: 1017

Here's a one-liner using the built-in filter function:

>>> d = {'a':1, 'b':2, 'c':3}
>>> dict(filter(lambda x: x[0] != 'c', d.items()))
{'a': 1, 'b': 2}

Upvotes: 1

minglyu
minglyu

Reputation: 3337

Dict comprehension seems to be more elegant

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

Upvotes: 3

Samsul Hadi 夏豪迪
Samsul Hadi 夏豪迪

Reputation: 13

solution from me

item = dict({"A": 1, "B": 3, "C": 4})
print(item)
{'A': 1, 'B': 3, 'C': 4}

new_dict = (lambda d: d.pop('C') and d)(item)
print(new_dict)
{'A': 1, 'B': 3}

Upvotes: 1

Felix Yuan
Felix Yuan

Reputation: 243

When you invoke pop the original dictionary is modified in place.

You can return that one from your function.

>>> a = {'foo': 1, 'bar': 2}
>>> a.pop('foo')
1
>>> a
{'bar': 2}

Upvotes: 8

z0r
z0r

Reputation: 8585

If you need an expression that does this (so you can use it in a lambda or comprehension) then you can use this little hack trick: create a tuple with the dictionary and the popped element, and then get the original item back out of the tuple:

(foo, foo.pop(x))[0]

For example:

ds = [{'a': 1, 'b': 2, 'c': 3}, {'a': 4, 'b': 5, 'c': 6}]
[(d, d.pop('c'))[0] for d in ds]
assert ds == [{'a': 1, 'b': 2}, {'a': 4, 'b': 5}]

Note that this actually modifies the original dictionary, so despite being a comprehension, it's not purely functional.

Upvotes: 18

jh314
jh314

Reputation: 27812

How about this:

{i:d[i] for i in d if i!='c'}

It's called Dictionary Comprehensions and it's available since Python 2.7.

or if you are using Python older than 2.7:

dict((i,d[i]) for i in d if i!='c')

Upvotes: 121

sinaiy
sinaiy

Reputation: 116

this will work,

(lambda dict_,key_:dict_.pop(key_,True) and dict_)({1:1},1)

EDIT this will drop the key if exist in the dictionary and will return the dictionary without the key,value pair

in python there are functions that alter an object in place, and returns a value instead of the altered object, {}.pop function is an example.

we can use a lambda function as in the example, or more generic below (lambda func:obj:(func(obj) and False) or obj) to alter this behavior, and get a the expected behavior.

Upvotes: 0

Gustav Larsson
Gustav Larsson

Reputation: 8497

Why not roll your own? This will likely be faster than creating a new one using dictionary comprehensions:

def without(d, key):
    new_d = d.copy()
    new_d.pop(key)
    return new_d

Upvotes: 31

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