From 3aa3c2b3ac470078933fa51d450e8d0d5d47f791 Mon Sep 17 00:00:00 2001
From: Connor Ward <c.ward20@imperial.ac.uk>
Date: Wed, 26 Aug 2026 13:06:34 +0100
Subject: [PATCH] Convert Python objects into strings

Makes it much more pleasant to construct preconditioners.
---
 petsctools/options.py          |  6 +++++-
 tests/docs/test_appctx_docs.py |  2 +-
 tests/test_options.py          | 34 ++++++++++++++++++++++++++++++++--
 3 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/petsctools/options.py b/petsctools/options.py
index 8d49215..5e382eb 100644
--- a/petsctools/options.py
+++ b/petsctools/options.py
@@ -434,7 +434,11 @@ def __init__(self, parameters: dict[str, Any],
         # Replace any Python objects in the parameters dict with appctx entries
         appmngr = AppContextManager()
         for key, value in parameters.items():
-            if not isinstance(value, _native_petsc_option_types):
+            # Convert Python objects into their string representation for
+            # things like 'pc_python_type' and 'snes_python_type'
+            if key.endswith("python_type") and isinstance(value, type):
+                parameters[key] = f"{value.__module__}.{value.__name__}"
+            elif not isinstance(value, _native_petsc_option_types):
                 parameters[key] = appmngr.add(value)
         self.appmngr = appmngr
 
diff --git a/tests/docs/test_appctx_docs.py b/tests/docs/test_appctx_docs.py
index 52914ad..b4d270c 100644
--- a/tests/docs/test_appctx_docs.py
+++ b/tests/docs/test_appctx_docs.py
@@ -104,7 +104,7 @@ def test_appctx_docs():
             'ksp_converged_reason': None,
             'ksp_type': 'richardson',
             'pc_type': 'python',
-            'pc_python_type': f'{__name__}.DiffusionJacobiPC',
+            'pc_python_type': DiffusionJacobiPC,
             'djacobi_scale': 0.9,
             'djacobi_sigma': sigma_p,
         },
diff --git a/tests/test_options.py b/tests/test_options.py
index d21c7a3..1fa3b0a 100644
--- a/tests/test_options.py
+++ b/tests/test_options.py
@@ -247,7 +247,8 @@ def apply(self, pc, x, y):
 
 @pytest.mark.skipnopetsc4py
 @pytest.mark.parametrize("use_prefix", ["with_prefix", "without_prefix"])
-def test_python_options_ksp(use_prefix):
+@pytest.mark.parametrize("use_pc_class", [False, True])
+def test_python_options_ksp(use_prefix, use_pc_class):
     PETSc = petsctools.init()
     n = 4
     sizes = (n, n)
@@ -264,10 +265,14 @@ def test_python_options_ksp(use_prefix):
     parameters = {
         'ksp_type': 'preonly',
         'pc_type': 'python',
-        'pc_python_type': f'{__name__}.JacobiTestPC',
         'jacobi_use_prefixed_options': use_prefix == "with_prefix",
         'jacobi_scale': diag,
     }
+    if use_pc_class:
+        parameters['pc_python_type'] = JacobiTestPC
+    else:
+        parameters['pc_python_type'] = f'{__name__}.JacobiTestPC'
+
     petsctools.set_from_options(
         ksp, parameters=parameters, options_prefix="myksp"
     )
@@ -284,6 +289,31 @@ def test_python_options_ksp(use_prefix):
     assert (x - xcheck).norm() < 1e-14
 
 
+class MyPythonSNES:
+    pass
+
+
+@pytest.mark.skipnopetsc4py
+@pytest.mark.parametrize("use_prefix",
+                         [True, False],
+                         ids=["with_prefix", "without_prefix"])
+def test_python_type_option(use_prefix):
+    from petsc4py import PETSc
+
+    options = petsctools.OptionsManager(
+        parameters={
+            "snes_type": "python",
+            "snes_python_type": MyPythonSNES,
+        },
+        options_prefix="prefix_" if use_prefix else None
+    )
+
+    with options.inserted_options():
+        opts = PETSc.Options(options.options_prefix)
+        assert opts["snes_python_type"] == f"{__name__}.MyPythonSNES", \
+               "Python type name was not inserted into the options dictionary"
+
+
 @pytest.mark.skipnopetsc4py
 @pytest.mark.parametrize("options_prefix", (None, "", "custom_"))
 def test_commandline_options(caplog, options_prefix):