Finding matching keys in two large dictionaries and doing it fast

Question

I am trying to find corresponding keys in two different dictionaries. Each has about 600k entries.

Say for example:

    myRDP = { 'Actinobacter': 'GATCGA...TCA', 'subtilus sp.': 'ATCGATT...ACT' }     myNames = { 'Actinobacter': '8924342' } 

I want to print out the value for Actinobacter (8924342) since it matches a value in myRDP.

The following code works, but is very slow:

    for key in myRDP:         for jey in myNames:             if key == jey:                 print key, myNames[key] 

I've tried the following but it always results in a KeyError:

    for key in myRDP:         print myNames[key] 

Is there perhaps a function implemented in C for doing this? I've googled around but nothing seems to work.

Thanks.

Answer 1

Use sets, because they have a built-in intersection method which ought to be quick:

myRDP = { 'Actinobacter': 'GATCGA...TCA', 'subtilus sp.': 'ATCGATT...ACT' } myNames = { 'Actinobacter': '8924342' }  rdpSet = set(myRDP) namesSet = set(myNames)  for name in rdpSet.intersection(namesSet):     print name, myNames[name]  # Prints: Actinobacter 8924342