ValueError: right keys must be sorted

This error occurs when working with dictionaries in Python and attempting to perform an operation that requires the keys to be sorted, but they are not.

For example, consider the following code:

my_dict = {'b': 2, 'a': 1, 'c': 3}
sorted_values = sorted(my_dict.values())

The above code attempts to sort the values of `my_dict`, but it does not specify which keys to sort them by. This results in a `ValueError` with the message "right keys must be sorted".

To fix this error, you need to sort the keys before performing the operation. You can do this using the `sorted()` function:

my_dict = {'b': 2, 'a': 1, 'c': 3}
sorted_keys = sorted(my_dict.keys())
sorted_values = [my_dict[key] for key in sorted_keys]

In the above code, we sort the keys of `my_dict` and then use a list comprehension to extract the sorted values. This will correctly sort the values and prevent the `ValueError`.