gh-37898: Deprecate `is_AbelianGroup`, `is_DualAbelianGroup`, `is_MatrixGroup`
    
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URL: #37898
Reported by: Matthias Köppe
Reviewer(s): Martin Rubey, Matthias Köppe, Vincent Delecroix

Author: Release Manager

src/sage/groups/abelian_gps/abelian_group.py

@@ -458,10 +458,16 @@ def is_AbelianGroup(x):
         sage: F = AbelianGroup(5,[5,5,7,8,9], names=list("abcde")); F
         Multiplicative Abelian group isomorphic to C5 x C5 x C7 x C8 x C9
         sage: is_AbelianGroup(F)
+        doctest:warning...
+        DeprecationWarning: the function is_AbelianGroup is deprecated;
+        use 'isinstance(..., AbelianGroup_class)' instead
+        See https://github.com/sagemath/sage/issues/37898 for details.
         True
         sage: is_AbelianGroup(AbelianGroup(7, [3]*7))
         True
     """
+    from sage.misc.superseded import deprecation
+    deprecation(37898, "the function is_AbelianGroup is deprecated; use 'isinstance(..., AbelianGroup_class)' instead")
     return isinstance(x, AbelianGroup_class)
 
 
@@ -569,7 +575,7 @@ def is_isomorphic(left, right):
             sage: G1.is_isomorphic(G2)
             True
         """
-        if not is_AbelianGroup(right):
+        if not isinstance(right, AbelianGroup_class):
             return False
         return left.elementary_divisors() == right.elementary_divisors()
 

src/sage/groups/abelian_gps/dual_abelian_group.py

@@ -86,6 +86,10 @@ def is_DualAbelianGroup(x):
         sage: F = AbelianGroup(5,[3,5,7,8,9], names=list("abcde"))
         sage: Fd = F.dual_group()
         sage: is_DualAbelianGroup(Fd)
+        doctest:warning...
+        DeprecationWarning: the function is_DualAbelianGroup is deprecated;
+        use 'isinstance(..., DualAbelianGroup_class)' instead
+        See https://github.com/sagemath/sage/issues/37898 for details.
         True
         sage: F = AbelianGroup(3,[1,2,3], names='a')
         sage: Fd = F.dual_group()
@@ -94,6 +98,8 @@ def is_DualAbelianGroup(x):
         sage: F.gens()
         (1, a1, a2)
     """
+    from sage.misc.superseded import deprecation
+    deprecation(37898, "the function is_DualAbelianGroup is deprecated; use 'isinstance(..., DualAbelianGroup_class)' instead")
     return isinstance(x, DualAbelianGroup_class)
 
 

src/sage/groups/matrix_gps/matrix_group.py

@@ -78,6 +78,10 @@ def is_MatrixGroup(x):
 
         sage: from sage.groups.matrix_gps.matrix_group import is_MatrixGroup
         sage: is_MatrixGroup(MatrixSpace(QQ, 3))
+        doctest:warning...
+        DeprecationWarning: the function is_MatrixGroup is deprecated;
+        use 'isinstance(..., MatrixGroup_base)' instead
+        See https://github.com/sagemath/sage/issues/37898 for details.
         False
         sage: is_MatrixGroup(Mat(QQ, 3))
         False
@@ -86,6 +90,8 @@ def is_MatrixGroup(x):
         sage: is_MatrixGroup(MatrixGroup([matrix(2, [1,1,0,1])]))
         True
     """
+    from sage.misc.superseded import deprecation
+    deprecation(37898, "the function is_MatrixGroup is deprecated; use 'isinstance(..., MatrixGroup_base)' instead")
     return isinstance(x, MatrixGroup_base)
 
 ###################################################################
@@ -499,7 +505,7 @@ def __richcmp__(self, other, op):
             sage: G != H
             False
         """
-        if not is_MatrixGroup(other):
+        if not isinstance(other, MatrixGroup_base):
             return NotImplemented
 
         if self is other:

src/sage/matrix/matrix_space.py

@@ -58,6 +58,7 @@
 from sage.features import PythonModule
 lazy_import('sage.matrix.matrix_gfpn_dense', ['Matrix_gfpn_dense'],
             feature=PythonModule('sage.matrix.matrix_gfpn_dense', spkg='meataxe'))
+lazy_import('sage.groups.matrix_gps.matrix_group', ['MatrixGroup_base'])
 
 _Rings = Rings()
 _Fields = Fields()
@@ -1451,14 +1452,8 @@ def _coerce_map_from_(self, S):
             pass
         else:
             MS = meth_matrix_space()
-
-            try:
-                from sage.groups.matrix_gps.matrix_group import is_MatrixGroup
-            except ImportError:
-                pass
-            else:
-                if is_MatrixGroup(S):
-                    return self.has_coerce_map_from(MS)
+            if isinstance(S, MatrixGroup_base):
+                return self.has_coerce_map_from(MS)
 
             try:
                 from sage.modular.arithgroup.arithgroup_generic import is_ArithmeticSubgroup

src/sage/modular/arithgroup/congroup_generic.py

@@ -89,9 +89,9 @@ def CongruenceSubgroup_constructor(*args):
         TypeError: Ring of definition must be Z / NZ for some N
     """
     from sage.groups.matrix_gps.finitely_generated import MatrixGroup
-    from sage.groups.matrix_gps.matrix_group import is_MatrixGroup
+    from sage.groups.matrix_gps.matrix_group import MatrixGroup_base
 
-    if is_MatrixGroup(args[0]):
+    if isinstance(args[0], MatrixGroup_base):
         G = args[0]
 
     elif isinstance(args[0], list):