How can I most effectively check for unique items in a list?

Question

let's say i have a list

li = [{'q':'apple','code':'2B'},
      {'q':'orange','code':'2A'},
      {'q':'plum','code':'2A'}]

What is the most efficient way to return the number of unique “codes” in this list? In this case, the unique codes are 2, since only 2B and 2A are unique.

I could put everything on a list and compare, but is it really effective?

Answer 1

Probably the most efficient simple way is to create a set of codes that will filter out uniques, and then get the number of elements in this set:

count = len(set(d["code"] for d in li))

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