REF: share IntervalIndex.intersection with Index.intersection

[jbrockmendel]

• closes BUG: find_common_type([interval[f8], interval[i8]]) returns object #38299
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

This changes the return dtype of IntervalIndex.intersection when that intersection is empty.

[jreback]

nice!

[jorisvandenbossche]

Can you also add tests for concat with interval dtypes? (that will also be affected by this change)

[jorisvandenbossche]

This is the wrong return value, see docstring in the base class:

pandas/pandas/core/dtypes/base.py

Lines 326 to 346 in 36c4d5c

	def _get_common_dtype(self, dtypes: List[DtypeObj]) -> Optional[DtypeObj]:
	"""
	Return the common dtype, if one exists.
	Used in `find_common_type` implementation. This is for example used
	to determine the resulting dtype in a concat operation.
	If no common dtype exists, return None (which gives the other dtypes
	the chance to determine a common dtype). If all dtypes in the list
	return None, then the common dtype will be "object" dtype (this means
	it is never needed to return "object" dtype from this method itself).
	Parameters
	----------
	dtypes : list of dtypes
	The dtypes for which to determine a common dtype. This is a list
	of np.dtype or ExtensionDtype instances.
	Returns
	-------
	Common dtype (np.dtype or ExtensionDtype) or None

[jbrockmendel]

thanks, will address in follow-up