check if a string contains character except the ones in a given string python

Question

How can I check if a string ( string1 ) contains characters except the ones in the following string ( seq_letters ):

string1 = 'SEQ'

seq_letters = 'ATCGRYMKSWHBVDN'

E and Q are not in seq_letters.

Answer 1

Using set.difference

string1 = 'SEQ'
seq_letters = 'ATCGRYMKSWHBVDN'

print(set(string1).difference(seq_letters))

Output:

{'E', 'Q'}

Answer 2

string1 = 'SEQ'
seq_letters = 'ATCGRYMKSWHBVDN'
result = []
for i in string1:
    if i not in seq_letters:
        result.append(i)
print(result)