IntervalIndex.get_loc can now look for exact matches only

Author: tp

doc/source/whatsnew/v0.23.0.txt

@@ -313,6 +313,7 @@ Other API Changes
 - :func:`DatetimeIndex.shift` and :func:`TimedeltaIndex.shift` will now raise ``NullFrequencyError`` (which subclasses ``ValueError``, which was raised in older versions) when the index object frequency is ``None`` (:issue:`19147`)
 - Addition and subtraction of ``NaN`` from a :class:`Series` with ``dtype='timedelta64[ns]'`` will raise a ``TypeError` instead of treating the ``NaN`` as ``NaT`` (:issue:`19274`)
 - Set operations (union, difference...) on :class:`IntervalIndex` with incompatible index types will now raise a ``TypeError`` rather than a ``ValueError`` (:issue:`19329`)
+- :meth:`IntervalIndex.get_loc` can now find exact matches only by setting ``method='exact'`` (:issue:`19349`)
 
 .. _whatsnew_0230.deprecations:
 

pandas/core/indexes/interval.py

@@ -837,7 +837,7 @@ def _maybe_cast_indexed(self, key):
         return key
 
     def _check_method(self, method):
-        if method is None:
+        if method in {None, 'exact'}:
             return
 
         if method in ['bfill', 'backfill', 'pad', 'ffill', 'nearest']:
@@ -911,8 +911,9 @@ def get_loc(self, key, method=None):
         Parameters
         ----------
         key : label
-        method : {None}, optional
+        method : {None, 'exact'}, optional
             * default: matches where the label is within an interval only.
+            * exact: exact matches only.
 
         Returns
         -------
@@ -940,12 +941,22 @@ def get_loc(self, key, method=None):
         >>> overlapping_index = pd.IntervalIndex.from_intervals([i2, i3])
         >>> overlapping_index.get_loc(1.5)
         array([0, 1], dtype=int64)
+
+        If you want to find exact matches only, use ``method='exact'``:
+
+        >>> index.get_loc(i1, method='exact')
+        0
+        >>> index.get_loc(pd.Interval(0,2), method='exact')
+        KeyError: Interval(0,2)
         """
         self._check_method(method)
 
         original_key = key
         key = self._maybe_cast_indexed(key)
 
+        if method == 'exact':
+            return super()._engine.get_loc(key)
+
         if self.is_non_overlapping_monotonic:
             if isinstance(key, Interval):
                 left = self._maybe_cast_slice_bound(key.left, 'left', None)

pandas/tests/indexes/interval/test_interval.py

@@ -666,6 +666,10 @@ def test_get_loc_value(self):
         idx = IntervalIndex.from_arrays([0, 2], [1, 3])
         pytest.raises(KeyError, idx.get_loc, 1.5)
 
+        # GH19349
+        with pytest.raises(KeyError):
+            self.index.get_loc(0.5, method='exact')
+
     # To be removed, replaced by test_interval_new.py (see #16316, #16386)
     def slice_locs_cases(self, breaks):
         # TODO: same tests for more index types
@@ -739,6 +743,10 @@ def test_get_loc_interval(self):
         pytest.raises(KeyError, self.index.get_loc, Interval(2, 3))
         pytest.raises(KeyError, self.index.get_loc,
                       Interval(-1, 0, 'left'))
+        # GH19349
+        assert self.index.get_loc(Interval(0, 1), method='exact') == 0
+        with pytest.raises(KeyError):
+            self.index.get_loc(Interval(0, 0.5), method='exact')
 
     # To be removed, replaced by test_interval_new.py (see #16316, #16386)
     def test_get_indexer(self):