Imk0tter

def alien(number,source,target): return __alien(_alien(number,source,len(number)),target)

def _alien(num,b1,l,mod=0):
    out = b1.index(num[l-1])*len(b1)**mod
    return out if l == 1 else out + _alien(num,b1,l-1,mod+1)

def __alien(num,b2):
    charset = b2
    l = len(b2)
    y = num%l
    out = charset[y]
    return out if num == y else __alien((num-y)/l,b2) + out