Trac #30266: hash function condition + treatment of restrictions

src/sage/manifolds/scalarfield.py

@@ -2180,6 +2180,8 @@ def restrict(self, subdomain):
                 resu = type(self)(subdomain.scalar_field_algebra(),
                                   coord_expression=sexpress, name=self._name,
                                   latex_name=self._latex_name)
+                if self.is_immutable():
+                    resu.set_immutable()  # restriction must be immutable, too
                 self._restrictions[subdomain] = resu
         return self._restrictions[subdomain]
 
@@ -3516,6 +3518,26 @@ def set_calc_order(self, symbol, order, truncate=False):
                 expr.simplify()
         self._del_derived()
 
+    def set_immutable(self):
+        r"""
+        Set ``self`` and all restrictions of ``self`` immutable.
+
+        EXAMPLES::
+
+            sage: M = Manifold(2, 'M')
+            sage: X.<x,y> = M.chart()
+            sage: U = M.open_subset('U', coord_def={X: x^2+y^2<1})
+            sage: f = M.scalar_field(x^2, name='f')
+            sage: fU = f.restrict(U)
+            sage: f.set_immutable()
+            sage: fU.is_immutable()
+            True
+
+        """
+        for rst in self._restrictions.values():
+            rst.set_immutable()
+        super().set_immutable()
+
     @cached_method
     def __hash__(self):
         r"""
@@ -3527,7 +3549,14 @@ def __hash__(self):
             sage: X.<x,y> = M.chart()
             sage: f = M.scalar_field(x^2, name='f')
             sage: f.set_immutable()
-            sage: hash(f) == f.__hash__()
+            sage: g = M.scalar_field(x^2, name='f')
+            sage: g.set_immutable()
+
+        Check whether equality implies equality of hash::
+
+            sage: f == g
+            True
+            sage: hash(f) == hash(g)
             True
 
         Let us check that ``f`` can be used as a dictionary key::
@@ -3539,4 +3568,4 @@ def __hash__(self):
         if self.is_mutable():
             raise ValueError('element must be immutable in order to be '
                              'hashable')
-        return hash((self._domain, repr(self)))
+        return hash(self._manifold)

src/sage/tensor/modules/free_module_tensor.py

@@ -1507,7 +1507,8 @@ def del_other_comp(self, basis=None):
             [Basis (e_1,e_2,e_3) on the Rank-3 free module M over the Integer Ring]
 
         """
-        if basis is None: basis = self._fmodule._def_basis
+        if basis is None:
+            basis = self._fmodule._def_basis
         if basis not in self._components:
             raise ValueError("the components w.r.t. the {}".format(basis) +
                              " have not been defined")
@@ -2368,8 +2369,8 @@ def __call__(self, *args):
             resu = 0
             for i in fmodule.irange():
                 resu += omega[[i]]*vv[[i]]
-            parent = resu.parent()
-            if resu is not parent.zero() and resu is not parent.one():
+            # Rename resu only if it is mutable and has no name yet:
+            if resu.is_mutable() and resu._name is None:
                 # Name and LaTeX symbol of the output:
                 if hasattr(resu, '_name'):
                     if self._name is not None and vector._name is not None: