Base conversion with arbitrary alphabets

baseconv.py

def baseconv(v1, a1, a2):
    if v1 == a1[0]: return a2[0]
    v2 = ""
    n1 = {c: i for i, c in enumerate(a1)}
    b1 = len(a1)
    b2 = len(a2)
    d1 = 0
    
    for i, c in enumerate(v1):
        d1 += n1[c] * pow(b1, len(v1) - i - 1)
    
    while d1:
        v2 = a2[d1 % b2] + v2
        d1 //= b2
        
    return v2