names_to_bands.setdefault(name,[]).append('Wings')

[chanisef]

The function in the cycle returns the name and name of the group Why would she add the name of the group to the existing name when retaking?

band1_names = ['John', 'George', 'Paul', 'Ringo']
band2_names = ['Paul']
names_to_bands = {}
for name in band1_names:
    names_to_bands.setdefault(name,['Beatles'])
for name in band2_names:
    names_to_bands.setdefault(name,[]).append('Wings')
print(names_to_bands['Paul'])
['Beatles', 'Wings']

P/S/ names_to_bands = {'John': ['Beatles'], 'George': ['Beatles'], 'Paul':

[guilherme]

You're using it wrong. setdefault combined with append♪ What's important is the challenge of this method and challenge. append independent.

setdefault returns value dict By the key. get or []and if there is no such key adds dict the value for the key given by the second parameter. And most importantly, append I'm calling for a list anyway.

It means this line:

names_to_bands.setdefault(name,[]).append('Wings')

It works as follows:

1. if name Total names_to_bands No, it's equivalent. names_to_bands[name] = ['Wings']
2. if name Total names_to_bands Yes, it is. names_to_bands[name].append('Wings')

I mean, with a re-call, you'll add a duplicate that you're watching.

What you need to do is:

bands = names_to_bands.setdefault(name,[])
if 'Wings' not in bands:
    bands.append('Wings')

or use it. set For the list:

names_to_bands.setdefault(name, set()).add('Wings')