my_base64.py

base64_list = []
for i in range(26):
    base64_list.append(chr(65+i))
for i in range(26):
    base64_list.append(chr(97+i))
for i in range(0,10):
    base64_list.append(str(i))
base64_list.extend(['+','/','='])
base64_dict = dict()

for i in range(65):
    base64_dict[base64_list[i]] = i


def toBase64(by):
    out = ''
    fin = len(by)%3
    for i,j,k in zip(by[0::3], by[1::3], by[2::3]):
        out += base64_list[i >> 2]
        out += base64_list[((i & 3) << 4)+(j >> 4)]
        out += base64_list[((j & 15) << 2)+(k >> 6)]
        out += base64_list[k & 63]
    if fin == 1:
        out += base64_list[by[-1] >> 2]
        out += base64_list[((by[-1] & 3) << 4)]
        out += '=='
    elif fin == 2:
        out += base64_list[by[-2] >> 2]
        out += base64_list[((by[-2] & 3) << 4)+(by[-1] >> 4)]
        out += base64_list[((by[-1] & 15) << 2)]
        out += '='
    return out


def bytesFromBase64(s):
    if len(s)%4 == 1:
        print("Invalid length !")
        return None
    elif len(s)%4 == 2:
        s += '=='
    elif len(s)%4 == 3:
        s += '='
    out = b''
    for i,j,k,l in zip(s[0::4], s[1::4], s[2::4], s[3::4]):
        i,j,k,l = base64_dict[i],base64_dict[j],base64_dict[k],base64_dict[l]
        if l != 64:
            out += bytes([(i << 2)+(j >> 4)])
            out += bytes([((j & 15) << 4)+(k >> 2)])
            out += bytes([((k & 3) << 6)+(l)])
        elif k != 64:
            out += bytes([(i << 2)+(j >> 4)])
            out += bytes([((j & 15) << 4)+(k >> 2)])
        else:
            out += bytes([(i << 2)+(j >> 4)])
    return out