Finance: Black Scholes Model not working

[buran]

OK, if I understand it correctly, I should add error handling to capture for incorrect input. Is that right?

It depend what you want - as it is now, you will get the same result if volatility is 0 or you don't supply argument for volatility at all. So, unless you change the code there will be no error, just be aware that volatility=0 will yield None for greeks.