TRAN

def tranration(s1,s2):
    transversion = 0
    transition = 0
    for i in range(len(s1)):
        if s1[i] != s2[i]:
            if s1[i] in 'AG' and s2[i] in 'AG' or s1[i] in 'CT' and s2[i] in 'CT':
                transition += 1
            else:
                transversion += 1
    return transition/transversion


with open('rosalind_tran.txt','r') as file:
    content = file.read()
DNAs_number, lines, line_number, DNAs = content.count('>'), content.splitlines(), 0, []
for i in range(DNAs_number):
    DNA = ''
    line_number += 1
    while lines[line_number][0] != '>':
        DNA += lines[line_number]
        line_number += 1
        if line_number+1 > len(lines):
            break
    DNAs.append(DNA)

print(tranration(DNAs[0]