display the units in _repr_inline_ and __repr__ (#325)

* properly pass a mapping of units

* add the units onto the inline repr

* simplify the formatting of the units

* also add a custom string `repr`

* closing parens

* make sure we always pass a dict of units

* expect init to fail on invalid units

* also change the replace test

* changelog

Author: keewis

docs/whats-new.rst

@@ -22,6 +22,8 @@ What's new
   By `Justus Magin <https://github.com/keewis>`_ and `Tom Nicholas <https://github.com/TomNicholas>`_.
 - Follow the change in signature of :py:meth:`xarray.Index.equals` (:issue:`322`, :pull:`324`)
   By `Justus Magin <https://github.com/keewis>`_.
+- Add units to the inline ``repr`` and define a custom ``repr`` (:issue:`308`, :pull:`325`)
+  By `Justus Magin <https://github.com/keewis>`_.
 
 0.5.1 (10 Aug 2025)
 -------------------

pint_xarray/index.py

@@ -15,6 +15,11 @@ def __init__(self, *, index, units):
         units : mapping of hashable to unit-like
             The units of the indexed coordinates
         """
+        if not isinstance(units, dict):
+            raise TypeError(
+                "Index units have to be a dict of coordinate names to units."
+            )
+
         self.index = index
         self.units = units
 
@@ -94,4 +99,14 @@ def __getitem__(self, indexer):
         return self._replace(self.index[indexer])
 
     def _repr_inline_(self, max_width):
-        return f"{self.__class__.__name__}({self.index.__class__.__name__})"
+        name = self.__class__.__name__
+        wrapped_name = self.index.__class__.__name__
+
+        formatted_units = {n: f"{u:~P}" for n, u in self.units.items()}
+        return f"{name}({wrapped_name}, units={formatted_units})"
+
+    def __repr__(self):
+        formatted_units = {n: f"{u:~P}" for n, u in self.units.items()}
+        summary = f"<{self.__class__.__name__} (units={formatted_units})>"
+
+        return "\n".join([summary, repr(self.index)])

pint_xarray/tests/test_conversion.py

@@ -252,7 +252,7 @@ def test_attach_units(self, type, units):
 
         index = PandasIndex(x, dim="x")
         if units.get("x") is not None:
-            index = PintIndex(index=index, units=units.get("x"))
+            index = PintIndex(index=index, units={"x": units.get("x")})
 
         obj = Dataset({"a": ("x", a), "b": ("x", b)}, coords={"u": ("x", u), "x": x})
         coords = Coordinates(

pint_xarray/tests/test_index.py

@@ -28,17 +28,24 @@ def indexer_equal(first, second):
 )
 @pytest.mark.parametrize("units", [ureg.Unit("m"), ureg.Unit("s")])
 def test_init(base_index, units):
-    index = PintIndex(index=base_index, units=units)
+    index = PintIndex(index=base_index, units={base_index.dim: units})
 
     assert index.index.equals(base_index)
-    assert index.units == units
+    assert index.units == {base_index.dim: units}
+
+
+def test_init_error():
+    base_index = PandasIndex(pd.Index([1, 2, 3]), dim="x")
+
+    with pytest.raises(TypeError, match="dict of coordinate names to units"):
+        PintIndex(index=base_index, units=ureg.Unit("s"))
 
 
 def test_replace():
-    old_index = PandasIndex([1, 2, 3], dim="y")
+    old_index = PandasIndex([1, 2, 3], dim="x")
     new_index = PandasIndex([0.1, 0.2, 0.3], dim="x")
 
-    old = PintIndex(index=old_index, units=ureg.Unit("m"))
+    old = PintIndex(index=old_index, units={"x": ureg.Unit("m")})
     new = old._replace(new_index)
 
     assert new.index.equals(new_index)
@@ -276,10 +283,23 @@ def test_getitem(indexer):
 
 @pytest.mark.parametrize("wrapped_index", (PandasIndex(pd.Index([1, 2]), dim="x"),))
 def test_repr_inline(wrapped_index):
-    index = PintIndex(index=wrapped_index, units=ureg.Unit("m"))
+    index = PintIndex(index=wrapped_index, units={"x": ureg.Unit("m")})
 
     # TODO: parametrize
     actual = index._repr_inline_(90)
 
     assert "PintIndex" in actual
     assert wrapped_index.__class__.__name__ in actual
+    assert "units" in actual
+
+
+@pytest.mark.parametrize("wrapped_index", (PandasIndex(pd.Index([1, 2]), dim="x"),))
+def test_repr(wrapped_index):
+    index = PintIndex(index=wrapped_index, units={"x": ureg.Unit("m")})
+
+    # TODO: parametrize
+    actual = repr(index)
+
+    assert "<PintIndex" in actual
+    assert "'x': 'm'" in actual
+    assert wrapped_index.__class__.__name__ in actual