implement ABCInterval (#19367)

Author: jbrockmendel

pandas/_libs/interval.pyx

@@ -109,6 +109,7 @@ cdef class Interval(IntervalMixin):
     cut, qcut : Convert arrays of continuous data into Categoricals/Series of
                 Interval.
     """
+    _typ = "interval"
 
     cdef readonly object left
     """Left bound for the interval"""

pandas/_libs/lib.pyx

@@ -41,7 +41,6 @@ from cpython.datetime cimport (PyDateTime_Check, PyDate_Check,
 PyDateTime_IMPORT
 
 from tslib import NaT, Timestamp, Timedelta, array_to_datetime
-from interval import Interval
 from missing cimport checknull
 
 

pandas/_libs/src/inference.pyx

@@ -37,7 +37,7 @@ cpdef bint is_decimal(object obj):
 
 
 cpdef bint is_interval(object obj):
-    return isinstance(obj, Interval)
+    return getattr(obj, '_typ', '_typ') == 'interval'
 
 
 cpdef bint is_period(object val):

pandas/core/dtypes/generic.py

@@ -54,6 +54,7 @@ def _check(cls, inst):
 ABCPeriod = create_pandas_abc_type("ABCPeriod", "_typ", ("period", ))
 ABCDateOffset = create_pandas_abc_type("ABCDateOffset", "_typ",
                                        ("dateoffset",))
+ABCInterval = create_pandas_abc_type("ABCInterval", "_typ", ("interval", ))
 
 
 class _ABCGeneric(type):

pandas/tests/dtypes/test_generic.py

@@ -45,6 +45,8 @@ def test_abc_types(self):
                           gt.ABCDateOffset)
         assert not isinstance(pd.Period('2012', freq='A-DEC'),
                               gt.ABCDateOffset)
+        assert isinstance(pd.Interval(0, 1.5), gt.ABCInterval)
+        assert not isinstance(pd.Period('2012', freq='A-DEC'), gt.ABCInterval)
 
 
 def test_setattr_warnings():