Merge branch 't/30181/immutable_elements_of_freemoduletensor' into t/…

…30310/immutability_of_chart_functions

src/sage/modules/free_module_element.pxd

@@ -1,7 +1,6 @@
 from sage.structure.element cimport Vector
 
 cdef class FreeModuleElement(Vector):
-    cdef bint _is_mutable
     cdef int set_unsafe(self, Py_ssize_t i, value) except -1
     cdef get_unsafe(self, Py_ssize_t i)
     cpdef int hamming_weight(self)

src/sage/modules/free_module_element.pyx

@@ -1485,53 +1485,6 @@ cdef class FreeModuleElement(Vector):   # abstract base class
         """
         return self.parent()([ a.subs(in_dict, **kwds) for a in self.list() ])
 
-    def set_immutable(self):
-        """
-        Make this vector immutable. This operation can't be undone.
-
-        EXAMPLES::
-
-            sage: v = vector([1..5]); v
-            (1, 2, 3, 4, 5)
-            sage: v[1] = 10
-            sage: v.set_immutable()
-            sage: v[1] = 10
-            Traceback (most recent call last):
-            ...
-            ValueError: vector is immutable; please change a copy instead (use copy())
-        """
-        self._is_mutable = 0
-
-    def is_mutable(self):
-        """
-        Return True if this vector is mutable, i.e., the entries can be
-        changed.
-
-        EXAMPLES::
-
-            sage: v = vector(QQ['x,y'], [1..5]); v.is_mutable()
-            True
-            sage: v.set_immutable()
-            sage: v.is_mutable()
-            False
-        """
-        return self._is_mutable
-
-    def is_immutable(self):
-        """
-        Return True if this vector is immutable, i.e., the entries cannot
-        be changed.
-
-        EXAMPLES::
-
-            sage: v = vector(QQ['x,y'], [1..5]); v.is_immutable()
-            False
-            sage: v.set_immutable()
-            sage: v.is_immutable()
-            True
-        """
-        return not self._is_mutable
-
     def change_ring(self, R):
         """
         Change the base ring of this vector.

src/sage/structure/element.pxd

@@ -191,6 +191,11 @@ cdef class ModuleElement(Element):
     # self._lmul_(x) is self * x
     cpdef _rmul_(self, Element left)
 
+cdef class ModuleElementWithMutability(ModuleElement):
+    cdef bint _is_mutable
+    cpdef bint is_immutable(self)
+    cpdef bint is_mutable(self)
+
 cdef class MonoidElement(Element):
     cpdef _pow_int(self, n)
 
@@ -234,7 +239,7 @@ cdef class InfinityElement(RingElement):
     pass
 
 
-cdef class Vector(ModuleElement):
+cdef class Vector(ModuleElementWithMutability):
     cdef Py_ssize_t _degree
 
     # Return the dot product using the simple metric

src/sage/structure/element.pyx

@@ -2350,6 +2350,69 @@ cdef class ModuleElement(Element):
         """
         raise NotImplementedError
 
+cdef class ModuleElementWithMutability(ModuleElement):
+    """
+    Generic element of a module with mutability.
+    """
+
+    def __init__(self, parent):
+        """
+        EXAMPLES::
+
+            sage: v = sage.modules.free_module_element.FreeModuleElement(QQ^3)
+            sage: type(v)
+            <type 'sage.modules.free_module_element.FreeModuleElement'>
+        """
+        self._parent = parent
+        self._is_mutable = 1
+
+    def set_immutable(self):
+        """
+        Make this vector immutable. This operation can't be undone.
+
+        EXAMPLES::
+
+            sage: v = vector([1..5]); v
+            (1, 2, 3, 4, 5)
+            sage: v[1] = 10
+            sage: v.set_immutable()
+            sage: v[1] = 10
+            Traceback (most recent call last):
+            ...
+            ValueError: vector is immutable; please change a copy instead (use copy())
+        """
+        self._is_mutable = 0
+
+    cpdef bint is_mutable(self):
+        """
+        Return True if this vector is mutable, i.e., the entries can be
+        changed.
+
+        EXAMPLES::
+
+            sage: v = vector(QQ['x,y'], [1..5]); v.is_mutable()
+            True
+            sage: v.set_immutable()
+            sage: v.is_mutable()
+            False
+        """
+        return self._is_mutable
+
+    cpdef bint is_immutable(self):
+        """
+        Return True if this vector is immutable, i.e., the entries cannot
+        be changed.
+
+        EXAMPLES::
+
+            sage: v = vector(QQ['x,y'], [1..5]); v.is_immutable()
+            False
+            sage: v.set_immutable()
+            sage: v.is_immutable()
+            True
+        """
+        return not self._is_mutable
+
 ########################################################################
 # Monoid
 ########################################################################
@@ -3099,7 +3162,7 @@ cdef class CommutativeRingElement(RingElement):
 
     ##############################################
 
-cdef class Vector(ModuleElement):
+cdef class Vector(ModuleElementWithMutability):
     cdef bint is_sparse_c(self):
         raise NotImplementedError
 

src/sage/tensor/modules/ext_pow_free_module.py

@@ -344,6 +344,7 @@ def zero(self):
             resu._add_comp_unsafe(basis)
             # (since new components are initialized to zero)
         resu._is_zero = True # This element is certainly zero
+        resu.set_immutable()
         return resu
 
     def _repr_(self):
@@ -804,6 +805,7 @@ def zero(self):
             resu._components[basis] = resu._new_comp(basis)
             # (since new components are initialized to zero)
         resu._is_zero = True # This element is certainly zero
+        resu.set_immutable()
         return resu
 
     def _repr_(self):

src/sage/tensor/modules/finite_rank_free_module.py

@@ -1992,6 +1992,7 @@ def zero(self):
             resu._add_comp_unsafe(basis)
             # (since new components are initialized to zero)
         resu._is_zero = True # This element is certainly zero
+        resu.set_immutable()
         return resu
 
     def dual(self):

src/sage/tensor/modules/free_module_linear_group.py

@@ -515,6 +515,7 @@ def one(self):
                                     start_index=fmodule._sindex,
                                     output_formatter=fmodule._output_formatter)
         resu._is_identity = True
+        resu.set_immutable()
         return resu
 
     #### End of monoid methods ####

src/sage/tensor/modules/free_module_tensor.py

@@ -195,7 +195,7 @@ class being:
 from __future__ import absolute_import
 
 from sage.rings.integer import Integer
-from sage.structure.element import ModuleElement
+from sage.structure.element import ModuleElementWithMutability
 from sage.tensor.modules.comp import (Components, CompWithSym, CompFullySym,
                                       CompFullyAntiSym)
 from sage.tensor.modules.tensor_with_indices import TensorWithIndices
@@ -206,7 +206,7 @@ class being:
 # TODO: remove the import of Chart after _preparse_display has been redefined
 # in tensor fields
 
-class FreeModuleTensor(ModuleElement):
+class FreeModuleTensor(ModuleElementWithMutability):
     r"""
     Tensor over a free module of finite rank over a commutative ring.
 
@@ -281,7 +281,7 @@ def __init__(self, fmodule, tensor_type, name=None, latex_name=None,
         """
         if parent is None:
             parent = fmodule.tensor_module(*tensor_type)
-        ModuleElement.__init__(self, parent)
+        super().__init__(parent)
         self._fmodule = fmodule
         self._tensor_type = tuple(tensor_type)
         self._tensor_rank = self._tensor_type[0] + self._tensor_type[1]
@@ -1319,17 +1319,17 @@ class :class:`~sage.tensor.modules.comp.Components`; if such
             [Basis (e_0,e_1,e_2) on the Rank-3 free module M over the Integer Ring,
              Basis (f_0,f_1,f_2) on the Rank-3 free module M over the Integer Ring]
 
-        Since zero is a special element, its components cannot be changed::
+        Since zero is an immutable element, its components cannot be changed::
 
             sage: z = M.tensor_module(1, 1).zero()
             sage: z.set_comp(e)[0,1] = 1
             Traceback (most recent call last):
             ...
-            AssertionError: the components of the zero element cannot be changed
+            AssertionError: the components of an immutable element cannot be changed
 
         """
-        if self is self.parent().zero():
-            raise AssertionError("the components of the zero element "
+        if self.is_immutable():
+            raise AssertionError("the components of an immutable element "
                                  "cannot be changed")
         self._is_zero = False  # a priori
         return self._set_comp_unsafe(basis)
@@ -1456,17 +1456,17 @@ class :class:`~sage.tensor.modules.comp.Components`;
             sage: t.display(e)
             t = -3 e_0*e^1 + 2 e_1*e^2
 
-        Since zero is a special element, its components cannot be changed::
+        Since zero is an immutable element, its components cannot be changed::
 
             sage: z = M.tensor_module(1, 1).zero()
             sage: z.add_comp(e)[0,1] = 1
             Traceback (most recent call last):
             ...
-            AssertionError: the components of the zero element cannot be changed
+            AssertionError: the components of an immutable element cannot be changed
 
         """
-        if self is self.parent().zero():
-            raise AssertionError("the components of the zero element "
+        if self.is_immutable():
+            raise AssertionError("the components of an immutable element "
                                  "cannot be changed")
         self._is_zero = False  # a priori
         return self._add_comp_unsafe(basis)

src/sage/tensor/modules/tensor_free_module.py

@@ -525,6 +525,7 @@ def zero(self):
             resu._add_comp_unsafe(basis)
             # (since new components are initialized to zero)
         resu._is_zero = True # This element is certainly zero
+        resu.set_immutable()
         return resu
 
     def _an_element_(self):