Check if a given key is contained in any of multiple dictionaries

Question

I have multiple dictionaries which contain data depending of their business value, e.g.:

companies = {'google': 'value_1', 'facebook': 'value_2'}
names = {'alex': 'value_3', 'john': 'value_4'}
...

I need to check whether a variable x is contained in any of these dictionaries, and to identify in which of these dictionaries it is contained. The number of such dictionaries can be huge, so checking them manually is not very effective. Is there something more pythonic than

if x in companies:
    pass    # do something
elif x in names:
    pass    # do something
...

Answer 1

Simple/quick to code: loop in the list of dictionaries, stop when you find it.

But complexity isn't good if you perform several searches. Instead, create a dictionary of your dictionaries.

• The keys are the union of keys
• The values are lists of couples (value, origin dict)

like this:

companies = {'google': 'value_1', 'facebook': 'value_2'}
names = {'alex': 'value_3', 'john': 'value_4'}

import collections

c = collections.defaultdict(list)

for d in [companies,names]:
    for k,v in d.items():
        c[k].append((v,d))

now:

print(c.get('google'))

prints:

[('value_1', {'google': 'value_1', 'facebook': 'value_2'})

Now if I add a common key in both dicts:

names = {'alex': 'value_3', 'john': 'value_4', 'facebook':'value_5'}
print(c.get('facebook'))

we get a list of all values and the origin dictionaries:

[('value_2', {'google': 'value_1', 'facebook': 'value_2'}),
 ('value_5', {'alex': 'value_3', 'john': 'value_4', 'facebook': 'value_5'})]

With that solution, even if you have a lot of dictionaries, the lookup is always O(1) once the new big dictionary is built. The build is amortized after 2 or 3 lookups.

Above, we see that the origin dictionary has been retained. Now you can choose how you identify this dictionary. I chose to put the reference itself as I had no constraint.