duplicate key storing

[snippsat]

Sound like defaultdict with list.

>>> from collections import defaultdict
>>> 
>>> d = defaultdict(list)
>>> s = [('green', 1), ('blue', 25), ('green', 100), ('blue', 4), ('red', 1)]
>>> for k, v in s:
...     d[k].append(v)
...     
>>> d.items()
dict_items([('green', [1, 100]), ('blue', [25, 4]), ('red', [1])])