Fix neuron_integrated_gradients pyre fixme issues (#1457)

Summary: Pull Request resolved: #1457

Differential Revision: D67523072

Author: Vivek Miglani

captum/_utils/gradient.py

@@ -28,6 +28,7 @@
 from captum._utils.sample_gradient import SampleGradientWrapper
 from captum._utils.typing import (
     ModuleOrModuleList,
+    SliceIntType,
     TargetType,
     TensorOrTupleOfTensorsGeneric,
 )
@@ -775,8 +776,11 @@ def compute_layer_gradients_and_eval(
 
 def construct_neuron_grad_fn(
     layer: Module,
-    # pyre-fixme[24]: Generic type `Callable` expects 2 type parameters.
-    neuron_selector: Union[int, Tuple[Union[int, slice], ...], Callable],
+    neuron_selector: Union[
+        int,
+        Tuple[Union[int, SliceIntType], ...],
+        Callable[[Union[Tensor, Tuple[Tensor, ...]]], Tensor],
+    ],
     device_ids: Union[None, List[int]] = None,
     attribute_to_neuron_input: bool = False,
     # pyre-fixme[24]: Generic type `Callable` expects 2 type parameters.

captum/_utils/typing.py

@@ -41,6 +41,13 @@
     TensorLikeList5D,
 ]
 
+try:
+    # Subscripted slice syntax is not supported in previous Python versions,
+    # falling back to slice type.
+    SliceIntType = slice[int, int, int]
+except TypeError:
+    # pyre-fixme[24]: Generic type `slice` expects 3 type parameters.
+    SliceIntType = slice  # type: ignore
 
 # Necessary for Python >=3.7 and <3.9!
 if TYPE_CHECKING:

captum/attr/_core/neuron/neuron_integrated_gradients.py

@@ -4,7 +4,7 @@
 from typing import Callable, List, Optional, Tuple, Union
 
 from captum._utils.gradient import construct_neuron_grad_fn
-from captum._utils.typing import TensorOrTupleOfTensorsGeneric
+from captum._utils.typing import SliceIntType, TensorOrTupleOfTensorsGeneric
 from captum.attr._core.integrated_gradients import IntegratedGradients
 from captum.attr._utils.attribution import GradientAttribution, NeuronAttribution
 from captum.log import log_usage
@@ -27,8 +27,7 @@ class NeuronIntegratedGradients(NeuronAttribution, GradientAttribution):
 
     def __init__(
         self,
-        # pyre-fixme[24]: Generic type `Callable` expects 2 type parameters.
-        forward_func: Callable,
+        forward_func: Callable[..., Tensor],
         layer: Module,
         device_ids: Union[None, List[int]] = None,
         multiply_by_inputs: bool = True,
@@ -76,8 +75,11 @@ def __init__(
     def attribute(
         self,
         inputs: TensorOrTupleOfTensorsGeneric,
-        # pyre-fixme[24]: Generic type `Callable` expects 2 type parameters.
-        neuron_selector: Union[int, Tuple[Union[int, slice], ...], Callable],
+        neuron_selector: Union[
+            int,
+            Tuple[Union[int, SliceIntType], ...],
+            Callable[[Union[Tensor, Tuple[Tensor, ...]]], Tensor],
+        ],
         baselines: Union[None, Tensor, Tuple[Tensor, ...]] = None,
         additional_forward_args: Optional[object] = None,
         n_steps: int = 50,