Functional differences between converting (List -> Dictionary -> List) vs (List -> Set -> List)?

Question

A list of unique elements can be attained by converting a list to a dictionary or a set, then back to a list.

>>> original_list = [1,2,3,4,5,6,7,8,9,2,4,6,8]
>>> original_list
[1, 2, 3, 4, 5, 6, 7, 8, 9, 2, 4, 6, 8]
>>> 
>>> unique_via_set = list(set(original_list))
>>> unique_via_dict = list(dict.fromkeys(original_list))
>>> 
>>> unique_via_set
[1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> unique_via_dict
[1, 2, 3, 4, 5, 6, 7, 8, 9]

^Python 3.7.3

Main Question:

What is the difference between these two strategies?

Sub Questions:

• Is one more efficient than the other?
• Is there a use case that is more optimized for one or the other?
• Is there a practical difference in the run time between these two strategies?

Note: I'm not looking for the best or fastest way to get unique elements from a list, I am looking to compare the two methods above

Edit: Again, I am not looking for HOW to remove duplicates, I am merely looking for the practical differences in the methods above, if any

Answer 1

While the implementations of the hash tables for dictionaries and sets may differ slightly, you will not see a functional difference between the keys of the dictionary and the set. The only major difference will be that the dictionary allocates a bunch of values referencing None, which the set does not need. That might make the dictionary implementation less efficient, since it is unnecessary overhead.