CODE EXAMPLE FOR PYTHON

python append value to dictionary list

import collections

a_dict = collections.defaultdict(list) # a dictionary key --> list (of any stuff)
a_dict["a"].append("hello")

print(a_dict)
>>> defaultdict(<class 'list'>, {'a': ['hello']})

a_dict["a"].append("kite")

print(a_dict)
>>> defaultdict(<class 'list'>, {'a': ['hello', 'kite']})