src/sage/groups/matrix_gps/matrix_group.py: Deprecate is_MatrixGroup

Author: Matthias Koeppe

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superseded import deprecation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()
@@ -1392,14 +1393,8 @@ 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):