DOC: Only implement __getitem__ if the wrapped class implements it.

QuLogic · QuLogic · commit dc89ababe367 · 2021-03-20T00:34:54.000-04:00
For example, this will be added for ndarray, but not float. Otherwise,
NumPy will treat float TaggedValue's as arrays when they aren't.
diff --git a/examples/units/basic_units.py b/examples/units/basic_units.py
@@ -122,6 +122,10 @@ def __new__(cls, value, unit):
         try:
             subcls = type(f'TaggedValue_of_{value_class.__name__}',
                           (cls, value_class), {})
+            if hasattr(value_class, '__getitem__'):
+                # Only implement `__getitem__` if the wrapped class implements
+                # it as well.
+                subcls.__getitem__ = subcls._getitem
             return object.__new__(subcls)
         except TypeError:
             return object.__new__(cls)
@@ -154,7 +158,12 @@ def __str__(self):
     def __len__(self):
         return len(self.value)
 
-    def __getitem__(self, key):
+    def _getitem(self, key):
+        # This implements `__getitem__`, but with a different name. This will
+        # be renamed on subclasses that wrap values that would have a
+        # `__getitem__` implementation (e.g., ndarray, but not float).
+        # Otherwise, NumPy will treat float TaggedValue's as arrays when they
+        # aren't.
         return TaggedValue(self.value[key], self.unit)
 
     def __iter__(self):
