Finding Commonalities in Two Dictionaries

Problem

You have two dictionaries and want to find out what they might have in common (same keys, same values, etc.).



In [1]:

    
a = {
'x' : 1,
'y' : 2,
'z' : 3 }

b = {
'w' : 10,
'x' : 11,
'y' : 2 }



In [2]:

    
# Find keys in common
a.keys() & b.keys() # { 'x', 'y' }









    Out[2]:





{'x', 'y'}



In [3]:

    
# Find keys in a that are not in b 
a.keys() - b.keys() # { 'z' }









    Out[3]:





{'z'}



In [4]:

    
# Find (key,value) pairs in common 
a.items() & b.items() # { ('y', 2) }









    Out[4]:





{('y', 2)}

These kinds of operations can also be used to alter or filter dictionary contents. For example, suppose you want to make a new dictionary with selected keys removed.



In [6]:

    
# Make a new dictionary with certain keys removed
c = {key:a[key] for key in a.keys() - {'z', 'w'}} 
# c is {'x': 1, 'y': 2}
print(c)









    



{'y': 2, 'x': 1}