Md null schema

[hyanwong]

While thinking with metadata for the tskit poster, I remembered this on the queue. As discussed with @benjeffery - this is mostly a documentation PR, but it also changes behaviour so that str(tskit.MetadataSchema(schema=None)) returns "Null_schema" rather than None, which was pretty confusing, because tskit.MetadataSchema(schema=None) is None always returns False.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.96%. Comparing base (4430763) to head (cc49b84).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2720      +/-   ##
==========================================
- Coverage   89.72%   86.96%   -2.77%     
==========================================
  Files          29       11      -18     
  Lines       31573    24358    -7215     
  Branches     6115     4501    -1614     
==========================================
- Hits        28328    21182    -7146     
+ Misses       1853     1817      -36     
+ Partials     1392     1359      -33     

Flag	Coverage Δ
c-tests	86.55% <ø> (ø)
lwt-tests	80.78% <ø> (ø)
python-c-tests	88.98% <ø> (ø)
python-tests	?

Flags with carried forward coverage won't be shown. Click here to find out more.

see 18 files with indirect coverage changes

[benjeffery]

LGTM!

[hyanwong]

Having looked at #2126, I wonder if, instead, we should report the str() as MetadataSchema(None), and indeed report all schemas like that? This would fully address #2126

[hyanwong]

I now think we should use this for the str representation of a schema:

    def __str__(self) -> str:
        if isinstance(self._schema, collections.OrderedDict):
            s = pprint.pformat(dict(self._schema))
        else:
            s = pprint.pformat(self._schema)
        if "\n" in s:
            return f"MetadataSchema(\n{s}\n)"
        else:
            return f"MetadataSchema({s})"

What do you think, @benjeffery ? Will this break anything?

[benjeffery]

I've rebased this and make the string tskit.MetadataSchema(None)

[benjeffery]

@Mergifyio rebase

[mergify]

rebase

✅ Branch has been successfully rebased