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

QuLogic · QuLogic · commit 513c00b56f06 · 2021-03-24T19:54:52.000-04:00
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
@@ -120,8 +120,13 @@ def __new__(cls, value, unit):
         # generate a new subclass for value
         value_class = type(value)
         try:
+            methods = {}
+            if hasattr(value_class, '__getitem__'):
+                # Only implement `__getitem__` if the wrapped class implements
+                # it as well.
+                methods['__getitem__'] = cls._getitem
             subcls = type(f'TaggedValue_of_{value_class.__name__}',
-                          (cls, value_class), {})
+                          (cls, value_class), methods)
             return object.__new__(subcls)
         except TypeError:
             return object.__new__(cls)
@@ -154,7 +159,12 @@ 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):
