def distance(strand_a, strand_b):
    if len(strand_a) != len(strand_b):
        raise ValueError('not of equal length')
    errors = [a!=b for a,b in zip(strand_a, strand_b)]
    return sum(errors)

#Calculate the Hamming difference between two DNA strands.
#
29c4a1ce8ea5820d31b45e0e298cf9c207efeab4
<mask token>

def distance(strand_a, strand_b):
    if len(strand_a) != len(strand_b):
        raise ValueError('not of equal length')
    errors = [(a != b) for a, b in zip(strand_a, strand_b)]
    return sum(errors)

def distance(strand_a, strand_b):
    if len(strand_a) != len(strand_b):
        raise ValueError('not of equal length')
    errors = [a!=b for a,b in zip(strand_a, strand_b)]
    return sum(errors)

#Calculate the Hamming difference between two DNA strands.
#