add property getters for all deprecated regionprops names

[grlee77]

Description

This is a backwards compatibility PR addressing the following issue raised on image.sc: https://forum.image.sc/t/scikit-image-regionprops-minor-axis-length-versus-axis-minor-length/59223/4. Prior to this PR, the old names were accessable via region['old_name'], but not via an attribute like region.old_name. After this PR, both forms of access will work.

I think we can drop all these old names for skimage2, but it is probably best to keep them working for now. To discourage use, these outdated names were not added to the regionprops function docstring and the autogenerated property docstrings have a line stating the property was deprecated.

I created a mixin class with the deprecated property methods by pasting the text output of the following script into _regionprops.py.

from skimage.measure._regionprops import PROPS

deprecated_props_class = "class DeprecatedProperties:\n"
for k, v in PROPS.items():

    deprecated_props_class += f"""
    @property
    def {k}(self):
        return self.{v}
    """
print(deprecated_props_class)

I thought about also adding a UserWarning to each outdated property, but was not sure it wouldn't be more annoying than useful.

Checklist

• Docstrings for all functions
• Gallery example in ./doc/examples (new features only)
• Benchmark in ./benchmarks, if your changes aren't covered by an
  existing benchmark
• Unit tests
• Clean style in the spirit of PEP8
• Descriptive commit messages (see below)

For reviewers

• Check that the PR title is short, concise, and will make sense 1 year
  later.
• Check that new functions are imported in corresponding __init__.py.
• Check that new features, API changes, and deprecations are mentioned in
  doc/release/release_dev.rst.

[grlee77]

I removed this if/else case since all old properties now have attributes via the DeprecatedProperties mixin class.

[jni]

@grlee77 perhaps we can keep this and just add the old property names to the dict?

[jni]

Oh right but that doesn't help with attribute access. Perhaps we can add a __getattr__ to the class?

[grlee77]

whoops. let me fix the conflicts here...

[grlee77]

This PR was updated to remove properties for the CamelCase names per discussion with @jni. Those have not been there for multiple releases without complaint, so let's not add them back in now...

[jni]

@grlee77 I'm approving, but what do you think of my suggestion of using a class getattr instead? I don't love that the old names now live in a dictionary and a class at the same time...

[pep8speaks]

Hello @grlee77! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2021-11-08 23:41:59 UTC

[grlee77]

@grlee77 I'm approving, but what do you think of my suggestion of using a class getattr instead? I don't love that the old names now live in a dictionary and a class at the same time...

There is already a __getattr__ to deal with extra user-provided properties, so we can just modify that. I just pushed a commit with this. If you don't like it we can revert it.

To prevent the user from being able to do assignments to the legacy property names (e.g. calling something like stats.major_axis_length = 5) I also implemented __setattr__ which will end up raising an AttributeError as it does for an @property without a setter. Also, this way also does not provide tab completion for the deprecated names when working interactively in an IPython terminal. I would argue that lack of tab-completion is probably a feature in this case, though, as we don't want new users discovering these deprecated property names!

[jni]

@grlee77 I like this better! I've just suggested reverting a couple of strange formatting choices. I'll try pushing them up to your branch.