CODEWITHSUNDEEP
python
Michael Tamillow
Michael Tamillow

Reputation: 425

Get the first value in a dictionary from a list of keys that occurs pythonically

I have a list of items that may or may not be keys in a dictionary. There is an order to the items. So I want to go from the first to the last and search for them in the dictionary. The first one to appear in the dictionary is the one that I want the value of. If none are in there, I want None.

I want this in a clean pythonic one liner, since it should be simple. I thought about something like this (but the syntax does not work):

value = dictionary.get(key) for key in list_of_keys while value == None

or maybe with if else like

value = dictionary.get(key) if key in dictionary or list_of_keys == [] else key = list_of_keys.pop()

but the second one only works if I initialize the key.

anyone got a simpler way to do this?

Upvotes: 1

Views: 114

Answers (3)

Rohan Vardhan
Rohan Vardhan

Reputation: 118

A simple solution with linear time complexity would be - 

d = dict()
# define your dict here

for k in list_of_keys:
    val = d.get(k, None) # you could also use try-except
    if val:
        print(val)
        break

Upvotes: 0

Pinyi Wang
Pinyi Wang

Reputation: 862

You can try this:

value = next((dictionary[key] for key in list_of_keys if key in dictionary), None)

Explanation:

(dictionary[key] for key in list_of_keys if key in dictionary) will create a python generator.

By using next, it will stop iterating through the python generator when the first valid key is found. If the generator is empty, it will return the second argument as the default value, in this case, None.

Upvotes: 3

SurpriseDog
SurpriseDog

Reputation: 484

value = [dictionary.get(key) for key in list_of_keys if key in dictionary][0]

This will work so long as there is as the dictionary contains at least one key in list_of_keys. It makes a list of the value of each key in list_of_keys and then [0] only outputs the first one.

Testing:

dictionary=dict(tom=9, bob=8, rose=4)
list_of_keys=['harry', 'sam', 'bob']
value = [dictionary.get(key) for key in list_of_keys if key in dictionary][0]
print(value)
8

Upvotes: 1

Related Questions