1-unittech.py

import numbers
def getNumber(s):
    try:
        return int(s)
    except ValueError:
        return float(s)
flag = True
while flag:
    try:
        score = raw_input('Enter score: ')
        if not isinstance(float(score), numbers.Real):
            raise Exception
        else:
            score = getNumber(score)
            if score >= 0.9:
                grade = 'A'
            elif score >= 0.8:
                grade = 'B'
            elif score >= 0.7:
                grade = 'C'
            print('Your grade is ' + grade)
    except:
        print('Only numbers are allowed')
    inp = raw_input('Do you want to continue?\n>')
    if inp == "no":
        print('You have quit the program')
        flag = False