Check if a string contains only given characters

Question

I\'m wondering if there is more elegant way to check if the string (str = \'abcccbbaabcbca\') contains only \'a\',\'b\' or \'c\' than iterating over it :

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Answer 1

Convert both strings to sets and check if they are equal. If yes, your string contains a AND b AND c:

valid = set(your_string) == set('abc')...

Use issubset to check if it contains ANY of a, b, c:

valid = set(your_string) <= set('abc')

or

valid = set(your_string).issubset('abc')

Subtract the sets to find out invalid characters:

bad_chars = set('abcXYcba') - set('abc') # set(X,Y)