Improve LayersHistogramsLogger to support inspecting multiple expli…

…citly named submodules (#177)

+ Fix outdated references to previous implementation in the docstring

vital/callbacks/debug.py

@@ -62,7 +62,7 @@ class LayersHistogramsLogger(Callback):
     def __init__(
         self,
         layer_types: Sequence[Union[str, Type[nn.Module]]],
-        submodule: str = None,
+        submodules: Sequence[str] = None,
         log_every_n_steps: int = 50,
         include_weight: bool = True,
         include_grad: bool = True,
@@ -71,17 +71,18 @@ def __init__(
 
         Args:
             layer_types: Types or classpaths of layers for which to log histograms.
-            submodule: Name of the module (e.g. 'encoder', 'classifier.', etc.) inside which to search for matching
-                layers. If none is provided, the Lightning module will be inspected starting from its root.
+            submodules: Name of the fields (e.g. 'encoder', 'classifier', etc.) corresponding to fields inside which to
+                search for matching layers. If none is provided, the Lightning module will be inspected starting from
+                its root.
             log_every_n_steps: Frequency at which to log the attention weights computed during the forward pass.
-            include_weight: Whether to log the layers' weights alongside the attention weights w.r.t the input tokens.
-            include_grad: Whether to log the layers' gradients alongside the attention weights w.r.t the input tokens.
+            include_weight: Whether to log the layers' weights.
+            include_grad: Whether to log the layers' gradients.
         """
         self.layer_types = [
             layer_type if not isinstance(layer_type, str) else import_from_module(layer_type)
             for layer_type in layer_types
         ]
-        self.submodule_name = submodule
+        self.submodule_names = submodules
 
         self.log_every_n_steps = log_every_n_steps
         self.train_step = 0
@@ -96,22 +97,27 @@ def setup(self, trainer: "pl.Trainer", pl_module: "pl.LightningModule", stage: O
             pl_module: `LightningModule` used in the experiment.
             stage: Current stage (e.g. fit, test, etc.) of the experiment.
         """
-        # Extract the requested submodule from the root module
-        module = pl_module
-        if self.submodule_name:
-            for submodule_name in self.submodule_name.split("."):
-                module = getattr(module, submodule_name)
 
         def _convert_camel_case_to_snake_case(string: str) -> str:
             return re.sub("(?!^)([A-Z]+)", r"_\1", string).lower()
 
-        # Get references to the specific layers to watch
+        # Extract the requested submodule from the root module
+        submodules_to_inspect = {"self": pl_module}
+        if self.submodule_names:
+            submodules_to_inspect = {}
+            for submodule_name in self.submodule_names:
+                # For each submodule, (recursively) follow the chain of attributes to get the actual submodule
+                module = pl_module
+                for submodule_name in submodule_name.split("."):
+                    module = getattr(module, submodule_name)
+                submodules_to_inspect[submodule_name] = module
+
+        # Get references to the specific layers to watch, prepending the submodule they're from to the layer name
         self.layers_to_log = {
-            f"{self.submodule_name}.{_convert_camel_case_to_snake_case(layer.__class__.__name__)}_{layer_idx}": layer
+            f"{submodule_name}.{_convert_camel_case_to_snake_case(layer.__class__.__name__)}_{layer_idx}": layer
+            for submodule_name, submodule in submodules_to_inspect.items()
             for layer_type in self.layer_types
-            for layer_idx, layer in enumerate(
-                submodule for submodule in module.modules() if isinstance(submodule, layer_type)
-            )
+            for layer_idx, layer in enumerate(layer for layer in submodule.modules() if isinstance(layer, layer_type))
         }
 
     def on_after_backward(self, trainer: "pl.Trainer", pl_module: "pl.LightningModule") -> None: