WIP: Namespaced AppContext

petsctools/__init__.py

@@ -1,3 +1,4 @@
+from .appctx import AppContext  # noqa: F401
 from .config import (  # noqa: F401
     MissingPetscException,
     get_config,

petsctools/appctx.py

@@ -0,0 +1,84 @@
+import itertools
+from functools import cached_property
+from petsctools.exceptions import PetscToolsAppctxException
+
+
+class _AppContextKey(int):
+    pass
+
+
+class AppContext:
+    """
+
+    .. code-block:: python3
+
+        appctx = AppContext()
+        some_data = MyCustomObject()
+
+        opts = OptionsManager(
+            parameters={
+                'pc_type': 'python',
+                'pc_python_type': 'MyCustomPC',
+                'custompc_somedata': appctx.add(some_data)},
+            options_prefix="")
+
+        with opts.inserted_options():
+            data = appctx.get('custompc_somedata')
+
+    """
+
+    def __init__(self):
+        self._count = itertools.count()
+        self._data = {}
+        self._missing_key = self._keygen()
+
+    def _keygen(self, key=None):
+        return _AppContextKey(next(self._count) if key is None else key)
+
+    def _option_to_key(self, option):
+        key = self.options_object.getInt(option, self.missing_key)
+        print(f"_option_to_key: {key = }")
+        return self._keygen(key)
+
+    @property
+    def missing_key(self):
+        """
+        Key instance representing a missing AppContext entry.
+        """
+        # PETSc requires the default value for Options.getObj()
+        # to be the correct type, so we need a dummy key.
+        return self._missing_key
+
+    def add(self, val):
+        """
+        Add a value to the application context and
+        return the autogenerated key for that value.
+
+        The autogenerated key should the value for the
+        corresponding entry in the solver_parameters dictionary.
+        """
+        key = self._keygen()
+        self._data[key] = val
+        print(f"add: {key = }")
+        return key
+
+    def __getitem__(self, option):
+        """
+        Return the value with the key saved in `PETSc.Options()[option]`.
+        """
+        try:
+            return self._data[self._option_to_key(option)]
+        except KeyError:
+            raise PetscToolsAppctxException(
+                f"AppContext does not have an entry for {option}")
+
+    def get(self, option, default=None):
+        key = self._option_to_key(option)
+        if key == self.missing_key:
+            return default
+        return self._data[key]
+
+    @cached_property
+    def options_object(self):
+        from petsc4py import PETSc
+        return PETSc.Options()

petsctools/exceptions.py

@@ -6,5 +6,9 @@ class PetscToolsNotInitialisedException(PetscToolsException):
     """Exception raised when petsctools should have been initialised."""
 
 
+class PetscToolsAppctxException(PetscToolsException):
+    """Exception raised when the Appctx is missing an entry."""
+
+
 class PetscToolsWarning(UserWarning):
     """Generic base class for petsctools warnings."""

tests/test_options.py

@@ -0,0 +1,24 @@
+import petsctools
+
+PETSc = petsctools.init()
+
+appctx = petsctools.AppContext()
+reynolds = 10
+
+opts = petsctools.OptionsManager(
+    parameters={
+        'fieldsplit_1_pc_type': 'python',
+        'fieldsplit_1_pc_python_type': 'firedrake.MassInvPC',
+        'fieldsplit_1_mass_reynolds': appctx.add(reynolds)},
+    options_prefix="")
+
+with opts.inserted_options():
+    re = appctx.get('fieldsplit_1_mass_reynolds')
+    print(f"{re = }")
+    re = appctx['fieldsplit_1_mass_reynolds']
+    print(f"{re = }")
+
+    re = appctx.get('fieldsplit_0_mass_reynolds', 20)
+    print(f"{re = }")
+    re = appctx['fieldsplit_0_mass_reynolds']
+    print(f"{re = }")