What happens when two elements in a dictionary use the same key?

In Python, a dictionary cannot contain two elements with the same key. If an element is added with a key that already exists, the value for that key is overwritten with the new one. For example:

my_dict = {'key': 'value1'}
my_dict['key'] = 'value2'
print(my_dict)  # {'key': 'value2'}

Thus, the last assigned element with this key is retained, and the previous one is removed.