Refactor upcast type check to check actual types rather than names

CHANGES

@@ -7,7 +7,7 @@ Pint Changelog
 - Improved compatbility for upcast types like xarray's DataArray or Dataset, to which
   Pint Quantities now fully defer for arithmetic and NumPy operations. A collection of
   basic tests for proper deferral has been added (for full integration tests, see
-  xarray's test suite). The list of names of upcast types is available at
+  xarray's test suite). The list of upcast types is available at
   `pint.compat.upcast_types` in the API.
   (Issue #959, Thanks Jon Thielen)
 - Moved docstrings to Numpy Docs

docs/numpy.rst

@@ -146,9 +146,9 @@ upcast types to which Pint defers (see
 - ``Series``, as defined by pandas
 - ``DataArray``, ``Dataset``, and ``Variable``, as defined by xarray
 
-If your application requires extension of this collection of types, the collection of
-type names is available in Pint's API at ``pint.compat.upcast_types``. Note that these
-are also the types to which a Quantity object will defer for arithmetic operations.
+If your application requires extension of this collection of types, it is available in
+Pint's API at ``pint.compat.upcast_types``. Note that these are also the types to which
+a Quantity object will defer for arithmetic operations.
 
 To achive these function and ufunc overrides, Pint uses the ``__array_function__`` and
 ``__array_ufunc__`` protocols respectively, as recommened by NumPy. This means that

pint/compat.py

@@ -149,12 +149,36 @@ def _to_magnitude(value, force_ndarray=False):
     babel_parse = babel_units = missing_dependency("Babel")  # noqa: F811
 
 # Define location of pint.Quantity in NEP-13 type cast hierarchy by defining upcast and
-# downcast/wrappable types
-upcast_types = ["PintArray", "Series", "DataArray", "Dataset", "Variable"]
+# downcast/wrappable types using guarded imports
+upcast_types = []
+
+# pint-pandas (PintArray)
+try:
+    from pintpandas import PintArray
+
+    upcast_types.append(PintArray)
+except ImportError:
+    pass
+
+# Pandas (Series)
+try:
+    from pandas import Series
+
+    upcast_types.append(Series)
+except ImportError:
+    pass
+
+# xarray (DataArray, Dataset, Variable)
+try:
+    from xarray import DataArray, Dataset, Variable
+
+    upcast_types += [DataArray, Dataset, Variable]
+except ImportError:
+    pass
 
 
 def is_upcast_type(other):
-    """Check if the type object is a upcast type.
+    """Check if the type object is a upcast type using preset list.
 
     Parameters
     ----------
@@ -164,8 +188,7 @@ def is_upcast_type(other):
     -------
     bool
     """
-    # Check if class name is in preset list
-    return other.__name__ in upcast_types
+    return other in upcast_types
 
 
 def eq(lhs, rhs, check_all):

pint/testsuite/test_quantity.py

@@ -12,6 +12,12 @@
 from pint.unit import UnitsContainer
 
 
+class FakeWrapper:
+    # Used in test_upcast_type_rejection_on_creation
+    def __init__(self, q):
+        self.q = q
+
+
 class TestQuantity(QuantityTestCase):
 
     FORCE_NDARRAY = False
@@ -536,12 +542,8 @@ def test_array_function_warning_on_creation(self):
     def test_no_ndarray_coercion_without_numpy(self):
         self.assertRaises(ValueError, self.Q_(1, "m").__array__)
 
-    @patch("pint.compat.upcast_types", ["FakeWrapper"])
+    @patch("pint.compat.upcast_types", [FakeWrapper])
     def test_upcast_type_rejection_on_creation(self):
-        class FakeWrapper:
-            def __init__(self, q):
-                self.q = q
-
         self.assertRaises(TypeError, self.Q_, FakeWrapper(42), "m")
         self.assertEqual(FakeWrapper(self.Q_(42, "m")).q, self.Q_(42, "m"))