[SPARK-26754][PYTHON] Add hasTrainingSummary to replace duplicate code in PySpark

[huaxingao]

What changes were proposed in this pull request?

Python version of #17654

How was this patch tested?

Existing Python unit test

[SparkQA]

Test build #101774 has finished for PR 23676 at commit 1d70ad1.

• This patch fails PySpark unit tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
• class LogisticRegressionModel(JavaModel, JavaClassificationModel, JavaMLWritable, JavaMLReadable,
• class GaussianMixtureModel(JavaModel, JavaMLWritable, JavaMLReadable, HasTrainingSummary):
• class KMeansModel(JavaModel, GeneralJavaMLWritable, JavaMLReadable, HasTrainingSummary):
• class BisectingKMeansModel(JavaModel, JavaMLWritable, JavaMLReadable, HasTrainingSummary):
• class LinearRegressionModel(JavaModel, JavaPredictionModel, GeneralJavaMLWritable, JavaMLReadable,
• class HasTrainingSummary(object):

[srowen]

The only issue I see here is that these properties were effectively added to subclasses in 2.0.0 and 2.1.0, so this seems somewhat misleading. Maybe we can declare these "since 2.1.0" as close enough?

[srowen]

You could also call "summary" directly though I suppose that would result in a different, possibly less useful error. I was also wondering whether RuntimeError is the right one, but I see other call sites above throw this when there is no summary.

Can you remove other checks for "if self.hasSummary" then, above? because when summary() is called it will now throw this error already.

[SparkQA]

Test build #101911 has finished for PR 23676 at commit 6308e62.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[srowen]

Pardon if you were already going to follow up on this, but I think you don't need to check self.hasSummary here and other classes anymore. The implementation in the new trait can do that in one place.

[srowen]

OK I get it, yeah, the polymorphism doesn't come across, and has to be mirrored in Python.

[srowen]

Merged to master

[huaxingao]

Thanks a lot for your help! @srowen