can one key have multiple values in dictionary python code example

Example 1: python dictionary multiple same keys

No, each key in a dictionary should be unique. 
You can’t have two keys with the same value. 
Attempting to use the same key again will just overwrite the previous value stored. 
If a key needs to store multiple values, 
then the value associated with the key should be a list or another dictionary.
Sourece: https://discuss.codecademy.com/t/can-a-dictionary-have-two-keys-of-the-same-value/351465

Example 2: how to have multiple values to a key in dict in python

from collections import defaultdict
 data = [(2010, 2), (2009, 4), (1989, 8), (2009, 7)]
 d = defaultdict(list)
print (d) # output --> defaultdict(<type 'list'>, {})
 for year, month in data:
     d[year].append(month) 
print (d) # output --> defaultdict(<type 'list'>, {2009: [4, 7], 2010: [2], 1989: [8]})

Example 3: dictionary multiple values per key

key = "somekey"
a.setdefault(key, [])
a[key].append(1)