Rot13 | 5 kyu

def rot13(message):
    a = {'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5,
            'f': 6, 'g': 7, 'h': 8, 'i': 9, 'j': 10,
            'k': 11, 'l': 12, 'm': 13, 'n': 14, 'o': 15,
            'p': 16, 'q': 17, 'r': 18, 's': 19, 't': 20,
            'u': 21, 'v': 22, 'w': 23, 'x': 24, 'y': 25,
            'z': 26}
    za = {'A': 1, 'B': 2, 'C': 3, 'D': 4, 'E': 5,
            'F': 6, 'G': 7, 'H': 8, 'I': 9, 'J': 10,
            'K': 11, 'L': 12, 'M': 13, 'N': 14, 'O': 15,
            'P': 16, 'Q': 17, 'R': 18, 'S': 19, 'T': 20,
            'U': 21, 'V': 22, 'W': 23, 'X': 24, 'Y': 25,
            'Z': 26}
    a2 = ['', 'a', 'b', 'c', 'd', 'e',
            'f', 'g', 'h', 'i', 'j',
            'k', 'l', 'm', 'n', 'o',
            'p', 'q', 'r', 's', 't',
            'u', 'v', 'w', 'x', 'y',
            'z']
    za2 = ['', 'A', 'B', 'C', 'D', 'E',
            'F', 'G', 'H', 'I', 'J',
            'K', 'L', 'M', 'N', 'O',
            'P', 'Q', 'R', 'S', 'T',
            'U', 'V', 'W', 'X', 'Y',
            'Z']
    text = ''
    for i in message:
        sch = 0
        if i in a:
            sch = a[i]
            for j in range(0, 13):
                sch += 1
            while sch > 26:
                sch -= 26
            text += a2[sch]
        elif i in za:
            sch = za[i]
            for j in range(0, 13):
                sch += 1
            while sch > 26:
                sch -= 26
            text += za2[sch]
        else:
            text += i
    return text