How do you check the presence of many keys in a Python dictinary?

Question

I have the following dictionary:

sites = {
    'stackoverflow': 1,
    'superuser': 2,
    'meta': 3,
    'serverfault': 4,
    'mathoverflow': 5
}

To check if there are more than one key available in the above dictionary, I will do something like:

'stackoverflow' in sites and 'serverfault' in sites

The above is maintainable with only 2 key lookups. Is there a better way to handle checking a large number of keys in a very big dictionary?

Answer 1

You could use all:

print( all(site in sites for site in ('stackoverflow','meta')) )
# True
print( all(site in sites for site in ('stackoverflow','meta','roger')) )
# False

Answer 2

How many lookups are you planning to do? I think the method you are using is fine.

If there are dozens, hundreds, etc of keys you are comparing against you could put all of the target keys in a list and then iterate over the list, checking to make sure each item is in the dictionary.

Answer 3

You can pretend the keys of the dict are a set, and then use set.issubset:

set(['stackoverflow', 'serverfault']).issubset(sites) # ==> True

set(['stackoverflow', 'google']).issubset(sites) # ==> False

Answer 4

mysites = ['stackoverflow', 'superuser']
[i for i in mysites if i in sites.keys()]  # ==> sites in the list mysites that are in your dictionary
[i for i in mysites if i not in sites.keys()]  # ==> sites in the list mysites that are not in your dictionary