BuiltinFunction._is_registered is giving false negatives

[ohanar]

This is easily encountered by the following:

sage: loads(dumps(sin)) == sin # derives from GinacFunction
True
sage: loads(dumps(cot)) == cot # should also be True
False

[ohanar]

The following seems to fix the issue:

@@ -853,18 +853,12 @@ cdef class BuiltinFunction(Function):
 
         # if match, get operator from function table
         global sfunction_serial_dict
-        if serial != -1 and sfunction_serial_dict.has_key(self._name) and \
-                sfunction_serial_dict[self._name].__class__ == self.__class__:
+        if serial != -1 and sfunction_serial_dict.has_key(serial) and \
+                sfunction_serial_dict[serial].__class__ == self.__class__:
                     # if the returned function is of the same type
                     self._serial = serial
                     return True
 
-        # search the function table to check if any of this type
-        for key, val in sfunction_serial_dict.iteritems():
-            if key == self._name and val.__class__ == self.__class__:
-                self._serial = key
-                return True
-
         return False
 
     def __reduce__(self):

I don't know the code, so I don't know what other implications this change might have (I didn't run the test suite).

[rws]

Cannot see any problems, long tests fine in symbolic. I adapted the patch to newer code, added a doctest for this.

---

New commits:

​4c04c34

Trac #15138: reviewer's patch: adapt to new code, add doctest