List of all unique characters in a string?

Question

I want to append characters to a string, but want to make sure all the letters in the final list are unique.

Example: \"aaabcabccd\" →

Answer 1

char_seen = []
for char in string:
    if char not in char_seen:
        char_seen.append(char)
print(''.join(char_seen))

This will preserve the order in which alphabets are coming,

output will be

abcd