partial match dictionary key(of tuples) in python

Question

I have a dictionary that maps 3tuple to 3tuple where key-tuples have some element in common

dict= { (a,b,c):(1,2,3),
        (a,b,d):tuple1,
        (a,e,b):         


        

Answer 1

You could reconstruct your dictionary into a triply nested dict.

dict= { ("foo", 4 , "q"): 9,
        ("foo", 4 , "r"): 8,
        ("foo", 8 , "s"): 7,
        ("bar", 15, "t"): 6,
        ("bar", 16, "u"): 5,
        ("baz", 23, "v"): 4
      }

d = {}
for (a,b,c), value in dict.iteritems():
    if a not in d:
        d[a] = {}
    if b not in d[a]:
        d[a][b] = {}
    d[a][b][c] = value

Here, d is equivalent to:

d = {
    "foo": {
        4:{
            "q": 9,
            "r": 8
        },
        8:{
            "s": 7
        }
    },
    "bar":{
        15:{
            "t": 6
        }
        16:{
            "u": 5
        }
    },
    "baz":{
        23{
            "v": 4
        }
    }
}

Now you can easily iterate through the possible third keys, given the first and second.

#find all keys whose first two elements are "foo" and 4
a = "foo"
b = 4
for c in d[a][b].iterkeys():
    print c

Result:

q
r

This only works for matching the third key. For instance, you wouldn't be able to find all second keys, given the third and the first.