I have 2 dictionaries (d3 and d4) and I want to see if the values of one of the dictionaries (d3) are in the keys of the another dictionary (d4) and in that case save the value of that dictionary (d4) into a new list.

```
d3 = {0: ['mo', 'A', 'la'], 1: ['tel', 'A', 'Al'], 2: ['Jak', 'E', 'Pum']}
d4 = {'ko' : 'Paul', 'la' : 'John', 'si' : 'Peter', 'Al' : 'Laura', 'gh' : 'Will'}
a3 = d3.values()
b3 = d3.keys()
a4 = d4.values()
b4 = d4.keys()
t = 0

for i in a3:    
if i not in b4 == -1:
    continue                 
else:          
    taxa = a4[t]
    t += 1 
print taxa

```

With this code I don't get the expected result, which should be: 

```
taxa = ['John', 'Laura']

```

In the case that a value of d3 is not in the keys of d4, it would be nice if it could return 'unknown' in the list. So the ideal result in this case would be like this:

```
taxa = ['John', 'Laura', 'unknown']

```

I have searched other questions and although some of them are similar,I haven't found any one explaining one case like this one