allow custom default options prefix (#22)

Author: JHopeCollins

petsctools/options.py

@@ -227,6 +227,12 @@ class OptionsManager:
         If no trailing underscore is provided, one is appended. Hence
         ``foo_`` and ``foo`` are treated equivalently. As an exception,
         if the prefix is the empty string, no underscore is appended.
+    default_prefix
+        The base string to generate default prefixes. If options_prefix
+        is not provided then a prefix is automatically generated with the
+        form "{default_prefix}_{n}", where n is a unique integer. Note that
+        because the unique integer is not stable any options passed via the
+        command line with a matching prefix will be ignored.
 
     See Also
     --------
@@ -240,19 +246,24 @@ class OptionsManager:
 
     count = itertools.count()
 
-    def __init__(self, parameters: dict, options_prefix: str | None):
+    def __init__(self, parameters: dict,
+                 options_prefix: str | None = None,
+                 default_prefix: str | None = None):
         super().__init__()
         if parameters is None:
             parameters = {}
         else:
             # Convert nested dicts
             parameters = flatten_parameters(parameters)
         if options_prefix is None:
-            self.options_prefix = "firedrake_%d_" % next(self.count)
+            default_prefix = default_prefix or "petsctools_"
+            if not default_prefix.endswith("_"):
+                default_prefix += "_"
+            self.options_prefix = f"{default_prefix}{next(self.count)}_"
             self.parameters = parameters
             self.to_delete = set(parameters)
         else:
-            if len(options_prefix) and not options_prefix.endswith("_"):
+            if options_prefix and not options_prefix.endswith("_"):
                 options_prefix += "_"
             self.options_prefix = options_prefix
             # Remove those options from the dict that were passed on
@@ -362,6 +373,7 @@ def attach_options(
     obj: petsc4py.PETSc.Object,
     parameters: dict | None = None,
     options_prefix: str | None = None,
+    default_prefix: str | None = None
 ) -> None:
     """Set up an OptionsManager and attach it to a PETSc Object.
 
@@ -373,6 +385,8 @@ def attach_options(
         The dictionary of parameters to use.
     options_prefix
         The options prefix to use for this object.
+    default_prefix
+        Base string for autogenerated default prefixes.
 
     See Also
     --------
@@ -385,7 +399,9 @@ def attach_options(
         )
 
     options = OptionsManager(
-        parameters=parameters, options_prefix=options_prefix
+        parameters=parameters,
+        options_prefix=options_prefix,
+        default_prefix=default_prefix,
     )
     obj.setAttr("options", options)
 
@@ -470,6 +486,7 @@ def set_from_options(
     obj: petsc4py.PETSc.Object,
     parameters: dict | None = None,
     options_prefix: str | None = None,
+    default_prefix: str | None = None,
 ) -> None:
     """Set up a PETSc object from the options in its OptionsManager.
 
@@ -491,6 +508,8 @@ def set_from_options(
         The dictionary of parameters to use.
     options_prefix
         The options prefix to use for this object.
+    default_prefix
+        Base string for autogenerated default prefixes.
 
     Raises
     ------
@@ -523,7 +542,9 @@ def set_from_options(
                 " provided to set_from_options"
             )
         attach_options(
-            obj, parameters=parameters, options_prefix=options_prefix
+            obj, parameters=parameters,
+            options_prefix=options_prefix,
+            default_prefix=default_prefix,
         )
 
     if is_set_from_options(obj):

tests/test_options.py

@@ -74,3 +74,25 @@ def test_unused_options(options_left):
     # Do we only raise a warning for the unused option?
     assert "optobj_not_used" in message
     assert "optobj_used" not in message
+
+
+@pytest.mark.skipnopetsc4py
+def test_options_prefix():
+    """Check that the OptionsManager sets the options prefix correctly.
+    """
+    # Generic default prefix
+    options = petsctools.OptionsManager({})
+    assert options.options_prefix.startswith("petsctools_")
+
+    # User defined default prefix
+    options = petsctools.OptionsManager({}, default_prefix="firedrake")
+    assert options.options_prefix.startswith("firedrake_")
+
+    # Explicit prefix overrides default prefix
+    options = petsctools.OptionsManager({}, options_prefix="myobj")
+    assert options.options_prefix.startswith("myobj_")
+
+    # Explicit prefix overrides default prefix
+    options = petsctools.OptionsManager({}, options_prefix="myobj",
+                                        default_prefix="firedrake")
+    assert options.options_prefix.startswith("myobj_")