Returning key of value found in dictionary using 'value in dict.values()'

Question

Is there a way to return the key for a match found in a dictionary using:

if val in dict.values():
# print the key of the value in the dictionary that matches val

I am trying to use the same search function, when looking for three different types of values. One is alphanumeric, the other is a string, and the third is a number. Within the search function I call the above code. In this function, I search through a dictionary containing known sets of these values (the three go together), trying to match the individual values read in from a file against these known sets in the dictionary. I have a search order (alphanumeric, string, number). The alphanumeric and number entries are one to one, but the string entry in the known dictionary is a list. I have been assuming that dict.iteritems() would not search through the string list for the unknown string, but that val in dict.values() would. Thus the use of the latter.

Depending on which matches (alphanumeric doesn't but number does, etc.), I wanted to return the key to know how the incoming data was matched against the known set.

So rather than writing two or three separate functions that for each key type, I was trying to use tricky dictionary code to keep it to one.

Edit:

So, suppose I have this dictionary:

dict = {'alphaNumeric':'A7', 'number':'36', 'string':['red','green','blue']}

and these incomplete sets of values to search against it:

sets = [['A7','',''],[['','36',''], ['','','green']]

I was trying to design on function to handle any searching:

def searchFun(sets, dict):
    for set in sets:
        for val in sets:
            if val in dict.values():
                return val, #KEY WHERE IT WAS FOUND#

Answer 1

You are using dictionaries backwards. You will have an easier time if you arrange them in the other direction:

my_dict = {'A7':'alphaNumeric', '36':'number', 'red':'string', 'green':'string', 'blue':'string'}
my_queries = ['A7', '', '', '', '36', '', '', '', 'green']

Note that your list of queries, being an irregular multi-dimensional list, should be flattened (there's a good method for that in the top answer in this question - you can tweak it to suit your version of Python if necessary). I've hard-coded it as a flat list to demonstrate the lookup function.

Now you can use a clean, concise function:

def searchfun(d, queries):
    return [(key,d[key]) for key in queries if key in d]

With the following result:

>>> searchfun(my_dict, my_queries)
[('A7', 'alphaNumeric'), ('36', 'number'), ('green', 'string')]

Also note that this is similar to OOP, with each object having an attribute that might be called something like self.classification.

Answer 2

Dictionaries are optimized to find the keys. There's no good way to look up by value. You just have to iterate it.

for k, v in dict.iteritems():
    if val == v:
        print k

Answer 3

No, there isn't. As @Laizer suggests, you can use .iteritems (or .items() in python3. But you can't do it with .values(). You could return one of the keys with that value however:

if val in dict.values():
    for k in dict.keys(): # of just `for x in dict:`
        if val == dict[k]:
             print k

Answer 4

There is no direct method to identify key based on values as multiple keys can have same value such as

mydict = {'orange': 0, 'red': 1, 'yellow': 2, 'black': 0}
print mydict.keys()[mydict.values().index(0)]

This will return you the first occurrence value 0 key that is 'orange'