Question

I have a function that can return one of three things:

• success (True)
• failure (False)
• error reading/parsing stream (None)

My question is, if I’m not supposed to test against True or False, how should I see what the result is. Below is how I’m currently doing it:

result = simulate(open("myfile"))
if result == None:
    print "error parsing stream"
elif result == True: # shouldn't do this
    print "result pass"
else:
    print "result fail"

is it really as simple as removing the == True part or should I add a tri-bool data-type. I do not want the simulate function to throw an exception as all I want the outer program to do with an error is log it and continue.

Answer 1

Don’t fear the Exception! Having your program just log and continue is as easy as:

try:
    result = simulate(open("myfile"))
except SimulationException as sim_exc:
    print "error parsing stream", sim_exc
else:
    if result:
        print "result pass"
    else:
        print "result fail"

# execution continues from here, regardless of exception or not

And now you can have a much richer type of notification from the simulate method as to what exactly went wrong, in case you find error/no-error not to be informative enough.