What's the best way to minimize the need of run time checks?

[Michael Selik]

On Tue, Aug 9, 2016 at 3:22 PM Juan Pablo Romero Méndez <
jpablo.romero at gmail.com> wrote:

> I'm actually looking for ways to minimize run time errors, so that would
> include TypeError and AttributeError.
>
> In your "File-like" example having type information would prevent me from
> even passing the wrong object, so I don't need to test for that particular
> problem.
>

Let's clarify this discussion by using the word "check" for type-checks
that necessary for the application to behave as desired and using the word
"test" for checking application behavior under normal and edge cases, such
as unexpected types being passed.

Are you saying you want to minimize type-checks during the execution of
your application? Or do you want to minimize the amount of testing code you
write?

I don't check for file-likeness in the application code. If somehow a
non-file-like (file-unlike?) object makes its way into my function, I
expect (and hope) my program will immediately stop and print a nice
traceback for me. If I wanted some other behavior, I probably would already
have try/except surrounding the appropriate section to deal with not-found
or permissions errors. If I need to, I'll add TypeError and AttributeError
to that except statement.

I sometimes write tests for unexpected inputs, checking to ensure that
either a TypeError or AttributeError is raised. However, sometimes I'm not
worried about it. If the user gives me bizarre input, they should know to
expect (possibly) bizarre results. Who knows, maybe that's what they wanted.

I would add type-checking or value-checking to my application if the wrong
type or value does not raise an error but instead causes an infinite loop
or corrupts data. Those situations are fairly rare.



On Tue, Aug 9, 2016 at 4:52 PM Juan Pablo Romero Méndez <
jpablo.romero at gmail.com> wrote:

> So as the writer of the function you expect the user to read the function
> body to determine what is safe to pass or not?


No. But I usually expect them to not freak out when they see a traceback.
Or if they do freak out, I want them to freak out and send a bug report.