Python: duplicate character encoding

The problem

Given a string, for each character return:

• ( — if the character appears only once in the whole string
• ) — if the character appears more than once

Comparison is case insensitive (Success treats s and S as the same character).

Examples:

• "din" → "((("
• "recede" → "()()()"
• "Success" → ")())())"
• "(( @" → "))(("

Approach

1. Lowercase — word.lower()
2. Find duplicates: characters where count > 1
3. For each character in the lowercase string, emit ( or ) depending on membership in the duplicate set

Solution

def duplicate_encode(word):
    lower_case_word = word.lower()
    duplicates = set([char for char in lower_case_word if lower_case_word.count(char) > 1])
    result = [")" if char in duplicates else "(" for char in lower_case_word]
    return "".join(result)

Examples

print(duplicate_encode("din"))      # (((
print(duplicate_encode("recede"))   # ()()()
print(duplicate_encode("Success"))  # )())())
print(duplicate_encode("(( @"))     # ))((

Summary

A duplicate set plus list comprehension — readable without regex or manual counting in a loop.