python dict fail

py_dict_fail.py

def foo():
    l = []
    return l[:]

#attr_map = dict.fromkeys(prefixes_unique, foo())

attr_map = dict.fromkeys(prefixes_unique, [])

for key in attr_map:
    print(key, id(attr_map[key]))

py_dict_pass.py

attr_map = dict(map(lambda prefix: (prefix, []), prefixes_unique))

for key in attr_map:
    print(key, id(attr_map[key]))