[FIX] Checks if Enum contains string (#119)

* Add test for issue #118

* Add MetaEnum to get desired behavior of in-operator

* Add FisherType and KFACType to init to make them easy to import

curvlinops/__init__.py

@@ -12,7 +12,7 @@
     NeumannInverseLinearOperator,
 )
 from curvlinops.jacobian import JacobianLinearOperator, TransposedJacobianLinearOperator
-from curvlinops.kfac import KFACLinearOperator
+from curvlinops.kfac import FisherType, KFACLinearOperator, KFACType
 from curvlinops.norm.hutchinson import HutchinsonSquaredFrobeniusNormEstimator
 from curvlinops.papyan2020traces.spectrum import (
     LanczosApproximateLogSpectrumCached,
@@ -33,6 +33,9 @@
     "KFACLinearOperator",
     "JacobianLinearOperator",
     "TransposedJacobianLinearOperator",
+    # Enums
+    "FisherType",
+    "KFACType",
     # inversion
     "CGInverseLinearOperator",
     "LSMRInverseLinearOperator",

curvlinops/kfac.py

@@ -19,7 +19,7 @@
 from __future__ import annotations
 
 from collections.abc import MutableMapping
-from enum import Enum
+from enum import Enum, EnumMeta
 from functools import partial
 from math import sqrt
 from typing import Any, Callable, Dict, Iterable, List, Optional, Tuple, TypeVar, Union
@@ -52,7 +52,18 @@
 ParameterMatrixType = TypeVar("ParameterMatrixType", Tensor, List[Tensor])
 
 
-class FisherType(str, Enum):
+class MetaEnum(EnumMeta):
+    """Metaclass for the Enum class for desired behavior of the `in` operator."""
+
+    def __contains__(cls, item):
+        try:
+            cls(item)
+        except ValueError:
+            return False
+        return True
+
+
+class FisherType(str, Enum, metaclass=MetaEnum):
     """Enum for the Fisher type."""
 
     TYPE2 = "type-2"
@@ -61,7 +72,7 @@ class FisherType(str, Enum):
     FORWARD_ONLY = "forward-only"
 
 
-class KFACType(str, Enum):
+class KFACType(str, Enum, metaclass=MetaEnum):
     """Enum for the KFAC approximation type."""
 
     EXPAND = "expand"

test/test_kfac.py

@@ -1270,3 +1270,21 @@ def test_from_state_dict():
     compare_state_dicts(kfac.state_dict(), kfac_new.state_dict())
     test_vec = rand(kfac.shape[1])
     report_nonclose(kfac @ test_vec, kfac_new @ test_vec)
+
+
+@mark.parametrize("fisher_type", ["type-2", "mc", "empirical", "forward-only"])
+@mark.parametrize("kfac_approx", ["expand", "reduce"])
+def test_string_in_enum(fisher_type: str, kfac_approx: str):
+    """Test whether checking if a string is contained in enum works.
+
+    To reproduce issue #118.
+    """
+    model = Linear(2, 2)
+    KFACLinearOperator(
+        model,
+        MSELoss(),
+        list(model.parameters()),
+        [(rand(2, 2), rand(2, 2))],
+        fisher_type=fisher_type,
+        kfac_approx=kfac_approx,
+    )