[Python-ideas] doctest

Devin Jeanpierre jeanpierreda at gmail.com
Fri Mar 2 07:55:05 CET 2012

> On Fri, Mar 2, 2012 at 7:36 AM, Steven D'Aprano <steve at pearwood.info> wrote:
>> Still, I reckon a directive is the right approach.

Why? That's how I do it because I am/was paranoid about compatibility,
but surely fixing dicts is important enough that, done right, nobody
would object if the semantics of comparison change subtly to allow for
unordered container comparison in the "natural" way?

(Is replying to a quoted quote acceptable on mailing lists?)

On Fri, Mar 2, 2012 at 12:56 AM, David Townshend <aquavitae69 at gmail.com> wrote:
> It seems that the problem with any solution based on interpreting repr
> (especially when nothing in know about the object) is that there are just
> too many exceptions.Another approach might be to allow for a custom
> compare function to be defined on doctest.  E.g., in the module to be
> tested:

The definition/use of an alternate comparison function needs to be
inside the doctests. Two issues:

Suppose we're running the doctests on module A, which defines a
different compare function. Module B also defines a different
comparison function, and is imported but not run as a doctest. Since
both of them did a global set-attribute to set the comparison
function, but B did it later, B wins and A's doctests are run under
the rules for module B.

Also, don't forget that doctests are quite often run in things that
are _not_ python source files. In particular, tutorial-like
documentation these days is frequently in the form of

> import doctest
> def _compare(got, expected):
>     return (sorted(eval(got)) == sorted(eval(expected)) or
>         doctest.compare(got, expected))
> doctest.usercompare = _compare

This function is wrong in the context of the above discussion. Why
sort a dict or set? Worse, why sort a list or tuple?

> The compare function would only need to deal with the idiosyncrasies of
> types actually used in doctests in that module.

Punting it to a user-defined function is nice for _really_ crazy
situations, but dicts and sets are not idiosyncratic or in any way
exceptional. doctest itself should handle them the way a naive user
would expect.

-- Devin

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