use python list comprehension to update dictionary value

Question

I have a list of dictionaries and would like to update the value for key ‘price’ with 0 if key price value is equal to ”

data=[a['price']=0 for a in data if a['price']=='']

Is it possible to do something like that? I have tried also with

a.update({'price':0})

but did not work as well…

Asked By: user2950162

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Source

Answer 1

Assignments are statements, and statements are not usable inside list comprehensions. Just use a normal for-loop:

data = ...
for a in data:
    if a['price'] == '':
        a['price'] = 0

And for the sake of completeness, you can also use this abomination (but that doesn’t mean you should):

data = ...

[a.__setitem__('price', 0 if a['price'] == '' else a['price']) for a in data]

Answered By: Markus Unterwaditzer

Answer 2

It is bad practice, but possible:

import operator

l = [
    {'price': '', 'name': 'Banana'},
    {'price': 0.59, 'name': 'Apple'},
    {'name': 'Cookie', 'status': 'unavailable'}
]

[operator.setitem(p, "price", 0) for p in l if "price" in p and not p["price"]]

The cases in which there’s no key “price” is handled and price is set to 0 if p["price"] is False, an empty string or any other value that python considers as False.

Note that the list comprehension returns garbage like [None].

Answered By: CodeManX

Answer 3

if you’re using dict.update don’t assign it to the original variable since it returns None

[a.update(price=0) for a in data if a['price']=='']

without assignment will update the list…

Answered By: Vinay G

Answer 4

Yes you can.

You can’t use update directly to dict because update is returns nothing and dict is only temporary variable in this case (inside list comprehension), so it will be no affect, but, you can apply it to iterable itself because iterable is persistance variable in this case.

instead of using

[my_dict['k'] = 'v' for my_dict in iterable]  # As I know, assignment not allowed in list comprehension

use

[iterable[i].update({'k': 'v'}) for i in range(len(iterable))]  # You can use enumerate also

So list comprehension itself will be return useless data, but your dicts will be updated.

Answered By: David Shiko

Answer 5

Dictionary comprehensions

data = [
    {'price': '', 'id': 0},
    {'price': 7, 'id': 1},
    {'price': 26, 'id': 2},
]
data = [{k: 0 for k in d if k == 'price'} if d['price'] == '' else d for d in data]
print(data)

[
    {'price': 0, 'id': 0},
    {'price': 7, 'id': 1},
    {'price': 26, 'id': 2},
]

Answered By: Iuri Guilherme

use python list comprehension to update dictionary value

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