Schema.extend is not compatible with Schema subclasses (affects pytest-voluptuous)

[himikof]

The pytest-voluptuous integration package makes use of a Schema subclass (S) to implement concise pytest assertion syntax.
It looks like this:

   assert S({
      'info': Partial({
          'package_url': 'https://pypi.org/project/pytest/',
          'platform': 'INVALID VALUE',
          'description': Length(max=10),
          'downloads': list,
          'classifiers': dict,
      }),
      'releases': dict,
      'urls': int
   }) == resp.json()

But the problem is that the S(...).extend returns Schema, not S, which breaks pytest integration after using extend.
If Schema.extend behaved more like a @classmethod and returned an instance of type(self), this use case would just work.

[alecthomas]

Seems reasonable. PRs welcome.

[svisser]

@himikof thanks for reporting this issue!

There is now a fix for this on the master branch so I'm closing this issue: e11b20a.