PYTHON

dictionary with list as value py

dict = {}
key = 1
value = "test"
dict.setdefault(key, []).append(value)

dictionary with list as values

word_freq = {'is': [1, 3, 4, 8, 10],
             'at': [3, 10, 15, 7, 9],
             'test': [5, 3, 7, 8, 1],
             'this': [2, 3, 5, 6, 11],
             'why': [10, 3, 9, 8, 12]}