new to Python - Checking user input return error on string not working
<p>I am trying to modify the code below to check the input from a  user. If the input is a string I want to generate an error see the function choiceTest(). But this doesn't work and I get the following exception, can you help
graham</p>

<pre><code>Choice your option:k
Traceback (most recent call last):
  File "C:\Users\Graham\bkup-workspaces\workspace\python-1\calculator.py", line 54, in &lt;module&gt;
    choice = menu()
  File "C:\Users\Graham\bkup-workspaces\workspace\python-1\calculator.py", line 18, in menu
    return input ("Choice your option:")    
  File "C:\Users\Graham\Desktop\letsussee\eclipse-java-helios-win32\eclipse\plugins\org.python.pydev_2.5.0.2012040618\PySrc\pydev_sitecustomize\sitecustomize.py", line 210, in input
    return eval(raw_input(prompt))
  File "&lt;string&gt;", line 1, in &lt;module&gt;
NameError: name 'k' is not defined
</code></pre>

<p>The code:</p>

<pre><code># calculator program

# NO CODE IS REALLY RUN HERE, IT IS ONLY TELLING US WHAT WE WILL DO LATER
# Here we will define our functions
# this prints the main menu, and prompts for a choice
def menu():
    #print what options you have

        print "Welcome to calculator.py"
        print "your options are:"
        print " "
        print "1) Addition"
        print "2) Subtraction"
        print "3) Multiplication"
        print "4) Division"
        print "5) Quit calculator.py"
        print " "
        return input ("Choice your option:")    
# this adds two numbers given

def add(a,b):
    print a, "+", b, "=", a + b

# this subtracts two numbers given
def sub(a,b):
    print b, "-", a, "=", b - a

# this multiplies two numbers given
def mul(a,b):
    print a, "*", b, "=", a * b

# this divides two numbers given
def div(a,b):
    print a, "/", b, "=", a / b

# decide if the choice is valid or not 
def choiceTest():


    isinstanceValue = isinstance(choice,int)
    instancevalueout = str(isinstanceValue)
    print "value is" + instancevalueout
    if not instancevalueout is "True":
       print " NOT AN INTEGER " + instancevalueout
       raise SystemExit

# NOW THE PROGRAM REALLY STARTS, AS CODE IS RUN
loop = 1
choice = 0
isinstanceValue = True
instancevalueout = ""

while loop == 1:
    choice = menu()
    choiceTest()
    if choice == 1:
        add(input("Add this: "),input("to this: "))
    elif choice == 2:
        sub(input("Subtract this: "),input("from this: "))
    elif choice == 3:
        mul(input("Multiply this: "),input("by this: "))
    elif choice == 4:
        div(input("Divide this: "),input("by this: "))
    elif choice == 5:
        loop = 0


print "Thankyou for using calculator.py!"

# NOW THE PROGRAM REALLY FINISHES
</code></pre>
