Enforce encoding. Maybe this will work for those getting the error?

def read_seqs(fasta):

    seqs = set()

    for  line in open(fasta):

    for  line in open(fasta, encoding="utf8", errors='ignore'):

        if line[0] == '>': continue

        seqs.add(normalize(str(line.strip())))

        seqs.add(normalize(str(line).strip()))

    return seqs

s1 = read_seqs(fasta1)