You can do something like this:
text="Hello this is a test"
unique_letters = set(text.lower())
unique_letters.remove(' ')
print(unique_letters)
print ('odd') if len(unique_letters) % 2 else print ('even')
Result:
{'o', 'h', 'e', 'l', 'i', 's', 'a', 't'}
even
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solved How to check the distinct number of characters in a string [closed]