binary to hex converter

bin_to_hex.py

# binary to hexidecimal
def bin_to_hex(num):
    total = ""
    subtotal = 0
    i = 0
    numstr = str(num)
    while(numstr):
        # foreach digit of the nibble (4 binary digits) translate into single hex digit
        # start from least sig digit
        subtotal = 0
        # pad front of numbers with 0's to fill to 4 bits
        if len(numstr) < 4:
            numstr = "0"*(4-len(numstr))+numstr
        for i in range(1,5):
            dig = numstr[-i]
            subtotal += int(dig) * int(pow(2,i-1))
        if (subtotal < 10):
            total = str(subtotal) + total
        else:
            # 65 - 9 = 
            total = chr(subtotal-10+65) + total
        # slice off last 4 bits and loop again
        numstr = numstr[:-4]    
    return total