Adding to the dictionary inside the for-loop - weird behaviour

[buran]

spam = ['foo', 'bar']
eggs = dict.fromkeys(spam, [])
print(eggs)
print([id(item) for item in eggs.values()])

Output:
{'foo': [], 'bar': []}
[140175770726664, 140175770726664]

lists are mutable and as you can see all keys refer to same object (same id). Update is reflected in all of them.

you can do eggs = {key:[] for key in spam}
alternatively, you can use collections.defaultdict with default value being list