Merge sagemath#34931

src/sage/rings/finite_rings/residue_field.pyx

@@ -160,9 +160,8 @@ from sage.rings.finite_rings.finite_field_ntl_gf2e import FiniteField_ntl_gf2e
 from sage.rings.finite_rings.finite_field_prime_modn import FiniteField_prime_modn
 from sage.rings.finite_rings.finite_field_pari_ffelt import FiniteField_pari_ffelt
 from sage.rings.ideal import is_Ideal
-from sage.structure.element cimport Element
+from sage.structure.element cimport Element, NumberFieldElement
 
-from sage.rings.number_field.number_field_element import is_NumberFieldElement
 from sage.rings.number_field.number_field_ideal import is_NumberFieldIdeal
 
 from sage.modules.free_module_element import FreeModuleElement
@@ -295,7 +294,7 @@ class ResidueFieldFactory(UniqueFactory):
             if not is_Ideal(p):
                 if isinstance(p, (int, Integer, Rational)):
                     p = ZZ.ideal(p)
-                elif is_NumberFieldElement(p):
+                elif isinstance(p, NumberFieldElement):
                     if p.parent().is_field():
                         p = p.parent().ring_of_integers().ideal(p)
                     else:

src/sage/rings/number_field/number_field_element.pxd

@@ -3,13 +3,15 @@ from sage.libs.gmp.types cimport mpz_t
 from sage.rings.integer cimport Integer
 from sage.rings.polynomial.polynomial_element cimport Polynomial
 from sage.structure.element cimport FieldElement, RingElement, ModuleElement
+from sage.structure.element cimport NumberFieldElement as NumberFieldElement_base
 from sage.structure.parent cimport Parent
 from sage.structure.parent_base cimport ParentWithBase
 from sage.libs.ntl.types cimport ZZ_c, ZZX_c
 from sage.libs.ntl.ntl_ZZX cimport ntl_ZZX
 from sage.libs.ntl.ntl_ZZ cimport ntl_ZZ
 
-cdef class NumberFieldElement(FieldElement):
+
+cdef class NumberFieldElement(NumberFieldElement_base):
     cdef ZZX_c __numerator
     cdef ZZ_c __denominator
     # Pointers to the defining polynomial (with numerator) for the field.

src/sage/rings/number_field/number_field_element.pyx

@@ -113,6 +113,10 @@ def is_NumberFieldElement(x):
         sage: is_NumberFieldElement(a+1)
         True
     """
+    from sage.misc.superseded import deprecation
+    deprecation(34931,
+                'is_NumberFieldElement is deprecated; '
+                'use isinstance(..., sage.structure.element.NumberFieldElement) instead')
     return isinstance(x, NumberFieldElement)
 
 
@@ -190,7 +194,7 @@ def _inverse_mod_generic(elt, I):
     return I.small_residue(y)
 
 
-cdef class NumberFieldElement(FieldElement):
+cdef class NumberFieldElement(NumberFieldElement_base):
     """
     An element of a number field.
 
@@ -3855,7 +3859,7 @@ cdef class NumberFieldElement(FieldElement):
         """
         from .number_field_ideal import is_NumberFieldIdeal
         if not is_NumberFieldIdeal(P):
-            if is_NumberFieldElement(P):
+            if isinstance(P, NumberFieldElement):
                 P = self.number_field().fractional_ideal(P)
             else:
                 raise TypeError("P must be an ideal")

src/sage/schemes/elliptic_curves/heegner.py

@@ -97,6 +97,7 @@
 from sage.misc.verbose import verbose
 from sage.misc.cachefunc import cached_method
 
+from sage.structure.element import NumberFieldElement
 from sage.structure.sage_object import SageObject
 from sage.structure.richcmp import (richcmp_method, richcmp,
                                     richcmp_not_equal, rich_to_bool)
@@ -2679,7 +2680,7 @@ def __init__(self, N, D, c=ZZ(1), f=None, check=True):
                 elif isinstance(f, BinaryQF):
                     # convert from BinaryQF
                     f = tuple(f)
-                elif sage.rings.number_field.number_field_element.is_NumberFieldElement(f):
+                elif isinstance(f, NumberFieldElement):
                     # tau = number field element
                     g = f.minpoly()
                     if g.degree() != 2:

src/sage/structure/element.pxd

@@ -230,6 +230,9 @@ cdef class EuclideanDomainElement(PrincipalIdealDomainElement):
 cdef class FieldElement(CommutativeRingElement):
     cpdef _floordiv_(self, other)
 
+cdef class NumberFieldElement(FieldElement):
+    pass
+
 cdef class AlgebraElement(RingElement):
     pass
 

src/sage/structure/element.pyx

@@ -46,6 +46,7 @@ abstract base classes.
                                 PrincipalIdealDomainElement
                                     EuclideanDomainElement
                         FieldElement
+                            NumberFieldElement
                         CommutativeAlgebraElement
                         Expression
                     AlgebraElement
@@ -4276,6 +4277,29 @@ cdef class FieldElement(CommutativeRingElement):
             other = self.parent()(other)
         return bool(self) or other.is_zero()
 
+
+cdef class NumberFieldElement(FieldElement):
+    r"""
+    Abstract base class for :class:`~sage.rings.number_field.number_field_element.NumberFieldElement`
+
+    This class is defined for the purpose of :func:`isinstance` tests.  It should not be
+    instantiated.
+
+    EXAMPLES::
+
+        sage: sage: k.<a> = NumberField(x^3 + x + 1)
+        sage: isinstance(a, sage.structure.element.NumberFieldElement)
+        True
+
+    By design, there is a unique direct subclass::
+
+        sage: len(sage.structure.element.NumberFieldElement.__subclasses__()) <= 1
+        True
+    """
+
+    pass
+
+
 def is_AlgebraElement(x):
     """
     Return ``True`` if x is of type AlgebraElement.