Inverting a dictionary with lists as values - Python Help

Question

The function down below, invert a dictionary that has lists as values, I wanted to understand how it works

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def invert_dict(d):
inverted = {}
for k in d:
for v in d[k]: #This Part
inverted.setdefault(v, []).append(k)#This part
return inverted
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This is the part that I didn't get if anyone can explain to me please, i'am beginner :

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for v in d[k]:
inverted.setdefault(v, []).append(k)
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Answer 1

I think there is no need of for loop inside for loop

inverted.setdefault(v,[]).append(k)

its a inbuild condition for inverting

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you can reduce for loops

def invert_dict(d):
inverted = {}
for k, v in d.iteritems():
inverted.setdefault(v, []).append(k)
return inverted

d = {###dictionary contents###}
print invert_dict(d)