Faster and more thorough detection of special method names

src/sage/misc/cachefunc.pyx

@@ -424,6 +424,21 @@ from sage.misc.sageinspect import sage_getfile, sage_getsourcelines, sage_getarg
 
 from weakref import WeakValueDictionary
 
+cdef frozenset special_method_names = frozenset(['__abs__', '__add__',
+            '__and__', '__call__', '__cmp__', '__coerce__', '__complex__', '__contains__', '__del__',
+            '__delattr__', '__delete__', '__delitem__', '__delslice__', '__dir__', '__div__',
+            '__eq__', '__float__', '__floordiv__', '__format__', '__ge__', '__get__', '__getattr__',
+            '__getattribute__', '__getitem__', '__getslice__', '__gt__', '__hash__', '__hex__',
+            '__iadd__', '__iand__', '__idiv__', '__ifloordiv__', '__ilshift__', '__imod__', '__imul__',
+            '__index__', '__init__', '__instancecheck__', '__int__', '__invert__', '__ior__', '__ipow__',
+            '__irshift__', '__isub__', '__iter__', '__itruediv__', '__ixor__', '__le__', '__len__',
+            '__length_hint__', '__long__', '__lshift__', '__lt__', '__missing__', '__mod__', '__mul__',
+            '__ne__', '__neg__', '__new__', '__nonzero__', '__oct__', '__or__', '__pos__', '__pow__',
+            '__radd__', '__rand__', '__rdiv__', '__repr__', '__reversed__', '__rfloordiv__', '__rlshift__',
+            '__rmod__', '__rmul__', '__ror__', '__rpow__', '__rrshift__', '__rshift__', '__rsub__',
+            '__rtruediv__', '__rxor__', '__set__', '__setattr__', '__setitem__', '__setslice__', '__sizeof__',
+            '__str__', '__sub__', '__subclasscheck__', '__truediv__', '__unicode__', '__xor__', 'next'])
+
 def _cached_function_unpickle(module,name):
     """
     Unpickling of cached functions.
@@ -2366,7 +2381,7 @@ def cached_method(f, name=None):
 
     """
     cdef str fname = name or f.__name__
-    if fname.startswith("__") and fname.endswith("__"):
+    if fname in special_method_names:
         return CachedSpecialMethod(f, name)
     return CachedMethod(f, name)