Fix failing tests with Pandas 1.3.0 (was: Add logic to deal with ABCIndexClass being renamed to ABCIndex)

[frreiss]

Pandas 1.3.x renamed its abstract base class for indexes from ABCIndexClass to ABCIndex, which is messing up some of our type checks. This PR adds some logic to work around that renaming. I'm using exceptions as control flow, which is a bit ugly, but the alternatives are also ugly.

[frreiss]

Okay, that didn't work. Will try something else.

[frreiss]

Fixed some bugs in SpanArray and TokenSpanArray that new regression tests in Pandas 1.3.0 brought to light. Now we're down to 62 failing tests.

[frreiss]

Update: Most of the test failures seem to be due to a bug in Pandas 1.3.0. Due to some performance optimizations introduced in https://github.com/pandas-dev/pandas/pull/40353, Pandas turns DataFrame.iloc[slice(x, y, z)] into __getitem__((..., slice(x, y, z)) on the ExtensionArray that backs any column defined with an extension type.

Code to reproduce:

from pandas.api.extensions import ExtensionArray,ExtensionDtype

class MyExtensionDtype(ExtensionDtype):
    """Minimal extension dtype"""
    def __init__(self):
        pass

    @property
    def type(self):
        return int

    @property
    def name(self) -> str:
        return "MyExtensionDtype"

    @classmethod
    def construct_array_type(cls):
        return MyExtensionArray()

class MyExtensionArray(ExtensionArray, ExtensionScalarOpsMixin):
    """Minimal extension array that logs calls to __getitem__()"""
    @property
    def dtype(self):
        return MyExtensionDtype()

    def copy(self):
        return MyExtensionArray()

    def __len__(self):
        return 5

    def __getitem__(self, key):
        print(f"__getitem__ called with key '{key}'")
        return 42

arr = MyExtensionArray()
df = pd.DataFrame({"a": arr})
_ = df.iloc[:3]

which prints out:

__getitem__ called with key '(Ellipsis, slice(None, 3, None))'

It should print the following instead:

__getitem__ called with key 'slice(None, 3, None)'

I'll put in a workaround tomorrow and file a bug with Pandas.

FYI @BryanCutler @ZachEichen @PokkeFe @Crushellini

[frreiss]

Update:

• Opened https://github.com/pandas-dev/pandas/issues/42430 to cover the slicing issue described above.
• Added a workaround for the Pandas issue to TensorArray.__getitem__()
• We're now down to 53 failing tests.

[frreiss]

Update: Fixed another minor bug. Now we are down to 49 failing tests.

[frreiss]

Update:

• Filed https://github.com/pandas-dev/pandas/issues/42437 and temporarily disabled the tests that that bug was causing to fail, since a workaround exists. See #221 for a workaround for that issue.
• Fixed a minor issue in TensorArray.isna() that was causing a number of regressions.

Now we're down to 2 failing tests.

[frreiss]

All tests passing against Pandas 1.3.0 now. Merging this PR to unblock other PRs.