what's wrong with exception handling
<p>When I enter a letter for one of the numbers I get an error:</p>

<pre><code>    Traceback (most recent call last):
      File "/Users/rodchar/Documents/Hello World Katie/testing.py", line 7, in &lt;module&gt;
        x = input("What is your first number?")
      File "&lt;string&gt;", line 1, in &lt;module&gt;
    NameError: name 's' is not defined



x = 0
y = 0

isValid = False

while isValid == False:
    x = input("What is your first number?")

    try:
        float(x)
        isValid = True
    except:
        isValid = False

    y = input("What is your second number?")

    try:
        float(y)
        isValid = True
    except:
        isValid = False


print "The answer is: %s" % (x+y)
</code></pre>
