def is_number():
    user_input = input ('>>> Please enter a temperature in Celsius: ')
    if (user_input.isdigit()):
        return user_input
    else:
        print ('It is not a number!')
        return is_number()
is_number()

t = input('>>> Please enter a temperature in Celsius: ')
def Celsius_to_Fahrenheit(t):
    fahrenheit = (t * 1.8) + 32
    print('>>> ' + str(t) + 'C' + ' converted to Fahrenheit is: ' +     str(fahrenheit) + 'F')
Celsius_to_Fahrenheit(float(t))