Fix docstring typo; exclude buffers

Doc/library/operator.rst

@@ -103,7 +103,7 @@ The mathematical and bitwise operations are the most numerous:
 
 .. function:: as_float(a)
 
-   Return *a* converted to an float.  Equivalent to ``float(a)``, except
+   Return *a* converted to a float.  Equivalent to ``float(a)``, except
    that conversion from a string or bytestring is not permitted. The result
    always has exact type :class:`float`.
 

Lib/operator.py

@@ -86,8 +86,20 @@ def as_float(obj):
 
     Same as float(obj), but does not accept strings.
     """
-    if isinstance(obj, (str, bytes, bytearray)):
-        raise TypeError("as_float argument must be numeric")
+    # Exclude strings and anything exposing the buffer interface.
+    bad_type = False
+    if isinstance(obj, str):
+        bad_type = True
+    else:
+        try:
+            memoryview(obj)
+            bad_type = True
+        except TypeError:
+            pass
+
+    if bad_type:
+        raise TypeError(f"must be real number, not {obj.__class__.__name__}")
+
     return float(obj)
 
 def floordiv(a, b):

Lib/test/test_operator.py

@@ -562,7 +562,12 @@ def __index__(self):
         self.assertIsFloatWithValue(operator.as_float(Confused()), 123.456)
 
         # Not convertible.
-        bad_values = ["123", b"123", bytearray(b"123"), None, 1j]
+        import array
+
+        bad_values = [
+            "123", b"123", bytearray(b"123"), None, 1j,
+            array.array('B', b"123.0"),
+        ]
         for bad_value in bad_values:
             with self.subTest(bad_value=bad_value):
                 with self.assertRaises(TypeError):