remove more duplicate code

Author: mantepse

src/sage/categories/rings.py

@@ -764,73 +764,6 @@ def unit_ideal(self):
             """
             return self._ideal_class_(1)(self, [self.one()])
 
-        def _ideal_class_(self, n=0):
-            r"""
-            Return a callable object that can be used to create ideals in this
-            ring.
-
-            EXAMPLES::
-
-                sage: MS = MatrixSpace(QQ, 2, 2)                                        # needs sage.modules
-                sage: MS._ideal_class_()                                                # needs sage.modules
-                <class 'sage.rings.noncommutative_ideals.Ideal_nc'>
-
-            Since :issue:`7797`, non-commutative rings have ideals as well::
-
-                sage: A = SteenrodAlgebra(2)                                                # needs sage.combinat sage.modules
-                sage: A._ideal_class_()                                                     # needs sage.combinat sage.modules
-                <class 'sage.rings.noncommutative_ideals.Ideal_nc'>
-            """
-            from sage.rings.noncommutative_ideals import Ideal_nc
-            return Ideal_nc
-
-        @cached_method
-        def zero_ideal(self):
-            """
-            Return the zero ideal of this ring (cached).
-
-            EXAMPLES::
-
-                sage: ZZ.zero_ideal()
-                Principal ideal (0) of Integer Ring
-                sage: QQ.zero_ideal()
-                Principal ideal (0) of Rational Field
-                sage: QQ['x'].zero_ideal()
-                Principal ideal (0) of Univariate Polynomial Ring in x over Rational Field
-
-            The result is cached::
-
-                sage: ZZ.zero_ideal() is ZZ.zero_ideal()
-                True
-
-            TESTS:
-
-            Make sure that :issue:`13644` is fixed::
-
-                sage: # needs sage.rings.padics
-                sage: K = Qp(3)
-                sage: R.<a> = K[]
-                sage: L.<a> = K.extension(a^2-3)
-                sage: L.ideal(a)
-                Principal ideal (1 + O(a^40)) of 3-adic Eisenstein Extension Field in a defined by a^2 - 3
-            """
-            return self._ideal_class_(1)(self, [self.zero()])
-
-        def principal_ideal(self, gen, coerce=True):
-            """
-            Return the principal ideal generated by gen.
-
-            EXAMPLES::
-
-                sage: R.<x,y> = ZZ[]
-                sage: R.principal_ideal(x+2*y)
-                Ideal (x + 2*y) of Multivariate Polynomial Ring in x, y over Integer Ring
-            """
-            C = self._ideal_class_(1)
-            if coerce:
-                gen = self(gen)
-            return C(self, [gen])
-
         def characteristic(self):
             """
             Return the characteristic of this ring.

src/sage/categories/rngs.py

@@ -97,7 +97,11 @@ def _ideal_class_(self, n=0):
             The argument `n`, standing for the number of generators
             of the ideal, is ignored.
 
-            EXAMPLES:
+            EXAMPLES::
+
+                sage: MS = MatrixSpace(QQ, 2, 2)                                        # needs sage.modules
+                sage: MS._ideal_class_()                                                # needs sage.modules
+                <class 'sage.rings.noncommutative_ideals.Ideal_nc'>
 
             Since :issue:`7797`, non-commutative rings have ideals as well::
 
@@ -153,4 +157,4 @@ def zero_ideal(self):
                 sage: L.ideal(a)
                 Principal ideal (1 + O(a^40)) of 3-adic Eisenstein Extension Field in a defined by a^2 - 3
             """
-            return self.principal_ideal(self.zero(), coerce=False)
+            return self._ideal_class_(1)(self, [self.zero()])