Python 2.7 Counting number of dictionary items with given value

This first part is mostly for fun -- I probably wouldn't use it in my code.

sum(d.values())

will get the number of True values. (Of course, you can get the number of False values by len(d) - sum(d.values())).

Slightly more generally, you can do something like:

sum(1 for x in d.values() if some_condition(x))

In this case, if x works just fine in place of if some_condition(x) and is what most people would use in real-world code)

OF THE THREE SOLUTIONS I HAVE POSTED HERE, THE ABOVE IS THE MOST IDIOMATIC AND IS THE ONE I WOULD RECOMMEND

Finally, I suppose this could be written a little more cleverly:

sum( x == chosen_value for x in d.values() )

This is in the same vein as my first (fun) solution as it relies on the fact that True + True == 2. Clever isn't always better. I think most people would consider this version to be a little more obscure than the one above (and therefore worse).

If you want a data structure that you can quickly access to check the counts, you could try using a Counter (as @mgilson points out, this relies on the values themselves being hashable):

>>> from collections import Counter
>>> d = {(1, 2): 2, (3, 1): 2, (4, 4): 1, (5, 6): 4}
>>> Counter(d.values())
Counter({2: 2, 1: 1, 4: 1})

You could then plug in a value and get the number of times it appeared:

>>> c = Counter(d.values())
>>> c[2]
2
>>> c[4]
1