x = raw_input("type a for decimal to binary, or b for binary to decimal: ")

if x == 'a':
    while True:
        try:
            n = int(raw_input("Enter your number, between 0 and 250: "))
            if 0 <= n <= 250:
                print n,"in binary is: {:08b}".format(n)
                break

            else:
                print n, "not in range, please try again.."

        except ValueError:
            print "invalid data found"

elif x == 'b':
    num2 = raw_input("Enter your number at most 8 digits long: ")

    while True:
        try:
            decimal = int(num2, 2)

            if len(num2)>8:
                print "binary number is too large"

            #got a valid binary number ==> terminate and exit loop
            else:  break

        except ValueError:
            print "Data entered is not a binary number"

        num2 = raw_input("please re-enter binary number: ")

    print "{0:08d} in decimal is: {1}".format(int(num2),decimal)