Ticket #14058: 14058-weak-binop.patch

sage/structure/coerce.pyx

@@ -80 +80 @@
 
 import operator
 
+from cpython.weakref cimport PyWeakref_GetObject, PyWeakref_NewRef
+
 from sage_object cimport SageObject
 from sage.categories.map cimport Map
 import sage.categories.morphism
@@ -92 +94 @@
 
 from coerce_actions import LeftModuleAction, RightModuleAction, IntegerMulAction
 
+cdef object coerce_to_left = "coerce_to_left"
+cdef object coerce_to_right = "coerce_to_right"
+
 cpdef py_scalar_parent(py_type):
     """
     Returns the Sage equivalent of the given python type, if one exists. 
@@ -228 +233 @@
         Now lets see what happens when we do a binary operations with
         an integer and a rational::
         
-            sage: left_morphism, right_morphism = maps[ZZ, QQ]
-            sage: print left_morphism
-            Natural morphism:
-              From: Integer Ring
-              To:   Rational Field
-            sage: print right_morphism
-            None
+            sage: maps[ZZ, QQ]
+            'coerce_to_right'
             
         We can see that it coerces the left operand from an integer to a 
         rational, and doesn't do anything to the right. 
@@ -1063 +1063 @@
             True
         """
         try:
-            return self._coercion_maps.get(R, S, None)
+            result = self._coercion_maps.get(R, S, None)
+            if result is None:
+                return None
+            elif result is coerce_to_left:
+                return None, R.coerce_map_from(S)
+            elif result is coerce_to_right:
+                return S.coerce_map_from(R), None
+            else:
+                codomain = <object>PyWeakref_GetObject(result)
+                if codomain is not None:
+                    return codomain.coerce_map_from(R), codomain.coerce_map_from(S)
         except KeyError:
-            homs = self.discover_coercion(R, S)
-            if 0:
-                # This breaks too many things that are going to change
-                # in the new coercion model anyways. 
-                # COERCE TODO: Enable it then. 
-                homs = self.verify_coercion_maps(R, S, homs)
+            pass
+        homs = self.discover_coercion(R, S)
+        if 0:
+            # This breaks too many things that are going to change
+            # in the new coercion model anyways. 
+            # COERCE TODO: Enable it then. 
+            homs = self.verify_coercion_maps(R, S, homs)
+        else:
+            if homs is not None:
+                x_map, y_map = homs
+                if x_map is not None and not isinstance(x_map, Map):
+                    raise RuntimeError, "BUG in coercion model: coerce_map_from must return a Map"
+                if y_map is not None and not isinstance(y_map, Map):
+                    raise RuntimeError, "BUG in coercion model: coerce_map_from must return a Map"
+        if homs is None:
+            result = None
+            swap = None
+        else:
+            R_map, S_map = homs
+            if R_map is None:
+                result = coerce_to_left
+                if PY_TYPE_CHECK(S, Parent) and (<Parent>S).has_coerce_map_from(R):
+                    swap = coerce_to_left
+                else:
+                    swap = coerce_to_right
+            elif S_map is None:
+                result = coerce_to_right
+                swap = coerce_to_left
             else:
-                if homs is not None:
-                    x_map, y_map = homs
-                    if x_map is not None and not isinstance(x_map, Map):
-                        raise RuntimeError, "BUG in coercion model: coerce_map_from must return a Map"
-                    if y_map is not None and not isinstance(y_map, Map):
-                        raise RuntimeError, "BUG in coercion model: coerce_map_from must return a Map"
-            if homs is None:
-                swap = None
-            else:
-                R_map, S_map = homs
-                if R_map is None and PY_TYPE_CHECK(S, Parent) and (<Parent>S).has_coerce_map_from(R):
-                    swap = None, (<Parent>S).coerce_map_from(R)
-                else:
-                    swap = S_map, R_map
-            self._coercion_maps.set(R, S, None, homs)
-            self._coercion_maps.set(S, R, None, swap)
+                result = swap = PyWeakref_NewRef(R_map.codomain(), None)
+        self._coercion_maps.set(R, S, None, result)
+        self._coercion_maps.set(S, R, None, swap)
         return homs
         
     cpdef verify_coercion_maps(self, R, S, homs, bint fix=False):