change base of integer

gistfile1.py

'''
convert a number (given in string format) from a base f to base t
'''

import string

def convertbase( n, f, t ) :    
    digits = list(string.digits+string.uppercase)
    rev_digits = {}

    for k,v in enumerate(digits) :
        rev_digits[v] = k

    # turn number to decimal    
    s = 0
    for i, c in enumerate(n) :
        s += rev_digits[n[i]]*(f**(len(n)-i-1))
    
    # turn number from decimal to t base
    res = ""
    while True :
        res = digits[s%t] + res        
        s = s // t # integer division
        if s == 0 :
            break

    return res

# some assertations
assert convertbase('1101', 2, 3) == '111'
assert convertbase('1101', 2, 10) == '13'