十六进制怎么转成10进制

def toDecimalNumber(char):
if char == "A":
return 10
elif char == "B":
return 11
elif char == "C":
return 12
elif char == "D":
return 13
elif char == "E":
return 14
elif char == "F":
return 15
else:
return int(char)
做完这个了，接下来该怎么办，是homework，急需答案

def toDecimalNumber(char): 
    if char == "A":
        return 10
    elif char == "B":
        return 11
    elif char == "C":
        return 12
    elif char == "D":
        return 13
    elif char == "E":
        return 14
    elif char == "F":
        return 15
    else:
        return int(char)

def hexToDecimal(hexStr):
    value = 0
    add = 0
    for i in range(len(hexStr)-1,-1,-1):
        value += toDecimalNumber(hexStr[i:i+1]) * 16**add
        add += 1
    return value

def main():
    a = input()
    print(hexToDecimal(a))