python 2.7 - Comparing two dictionary keys and values -

i have 2 dictionaries in i'm trying first find matching key d1 in d2, output subtraction of 3rd value in key both dictionaries..can done in 1 loop function? first tried doing in 2 steps gives me empty list d3, tried use loop gives me error v not defined.

d1 = {'alpha': [5, 9, 11], 'beta': [6, 10, 20], 'gamma': [12, 15, 19]} d2 = {'alpha': [3, 8, 20], 'omega': [15, 32, 40], 'ro': [22, 25, 4]}  d3 = {} key in d1:     if key in d2:         d3.setdefault(key, []).append print d3 #should d3 = {'alpha': [3, 8, 20]}  #compare , calculate difference between 20 , 11 in alpha key value = d3(key, v(2)) - d1(key, v(2)) print value #value = 9  #can loop find key in d2 , matches key in d1 #and calculate difference? key in d1:     if key in d2:         value = d2(key, v(2)) - d1(key, v(2))         print value 

thoughts?

thank you. -jon

you use dictionary comprehension:

diff = {key: d2[key][2] - d1[key][2] key in d2 if key in d1} # {'alpha': 9} 

this give dictionary in keys common d2 , d1 , values difference of third values in lists of d1 , d2