Python -将包含重复值的列表合并到字典时出现的问题

my_list = [("key1", "value1"), ("key2", "value2"), ("key1", "value3")]

my_dict = dict((x, y) for x, y in my_list)
print(my_dict)

{'key1': 'value3', 'key2': 'value2'}

from collections import defaultdict

my_list = [("key1", "value1"), ("key2", "value2"), ("key1", "value3")]

my_dict = defaultdict(list)
for key, value in my_list:
    my_dict[key].append(value)

print(dict(my_dict))

{'key1': ['value1', 'value3'], 'key2': ['value2']}