How much sanity checking is required for function inputs?

[Michael Selik]

On Mon, Apr 18, 2016 at 1:05 AM Christopher Reimer <
christopher_reimer at icloud.com> wrote:

> On 4/17/2016 3:18 PM, Michael Selik wrote:
>
> > I'd rather turn the question around: how much sanity checking is
> > necessary or useful? You'll find the answer is "surprisingly little"
> > compared to your experience in Java.
>
> I'm looking for a pythonic approach to sanity checking. From what I read
> elsewhere, sanity checking belongs in the unit tests and/or library
> classes designed for other people to use. I haven't seen many examples
> of sanity checks that is common in Java.
>
> > For example, you don't need to
> > explicitly check whether the color is present in your dictionary,
> > because it'll give you a KeyError if you look up a bad key.
>
> Without the sanity check against the constant dictionary, the color
> variable could be anything (it should be a string value). Looking at the
> code again, I should relocate the sanity checks in the Piece base class.
>

Why relocate rather than remove? What message would you provide that's
better than ``KeyError: 42`` with a traceback that shows exactly which
dictionary is being used and how?

> Why does the len of positions need to be 16?
>
> The positions variable is list of coordinates for 16 chess pieces (eight
> pawns, two rooks, two knights, two bishops, a king and a queen) for each
> color, locating the pieces on either the bottom quarter (i.e., [(1,1),
> ..., (2,8)]) or the top quarter (i.e., [(7,1), ..., (8,8)]) of the board.
>

I meant, what goes wrong if the number of positions input is other than 16?
Without these "sanity" checks, your functions might be reusable in, say, a
checkers game.