Update error messages

Remove "which should never happen" from them

Author: ssinhaleite

sinabs/backend/dynapcnn/dynapcnnnetwork_module.py

@@ -170,7 +170,7 @@ def get_dynapcnnlayers_edges(self) -> Set[Edge]:
 
         Returns
         ----------
-        - dcnnl_edges: a set of edges using the IDs of `DynapcnnLayer` instances. These edges describe the computational
+        - dcnnl_edges (Set): a set of edges using the IDs of `DynapcnnLayer` instances. These edges describe the computational
             graph implemented by the layers of the model (i.e., how the `DynapcnnLayer` instances address each other).
         """
         dcnnl_edges = set()

sinabs/backend/dynapcnn/exceptions.py

@@ -1,7 +1,7 @@
 from typing import Set, Tuple, Type
 
 default_invalid_structure_string = (
-    "This should never happen, but is most likely due to an unsupported SNN "
+    "Invalid structure found. This is most likely due to an unsupported SNN "
     "architecture. In general, a dynapcnn network should consist of groups of "
     "a weight layer (conv or linear), a spiking layer (IAFSqueeze), and "
     "optionally a pooling layer."

sinabs/backend/dynapcnn/sinabs_edges_handler.py

@@ -984,23 +984,23 @@ def verify_layer_info(
     for idx, info in dynapcnn_layer_info.items():
         if not "conv" in info:
             raise InvalidGraphStructure(
-                f"DynapCNN layer {idx} has no weight assigned, which should "
-                "never happen. " + default_invalid_structure_string
+                f"DynapCNN layer {idx} has no weight assigned. "
+                + default_invalid_structure_string
             )
         if not "neuron" in info:
             raise InvalidGraphStructure(
-                f"DynapCNN layer {idx} has no spiking layer assigned, which "
-                "should never happen. " + default_invalid_structure_string
+                f"DynapCNN layer {idx} has no spiking layer assigned. "
+                + default_invalid_structure_string
             )
         if not "destinations" in info:
             raise InvalidGraphStructure(
-                f"DynapCNN layer {idx} has no destination info assigned, which "
-                "should never happen. " + default_invalid_structure_string
+                f"DynapCNN layer {idx} has no destination info assigned. "
+                + default_invalid_structure_string
             )
     if edge_counts is not None:
         # Make sure there are as many layers as edges from weight to neuron
         if edge_counts.get("weight-neuron", 0) - len(dynapcnn_layer_info) > 0:
             raise InvalidGraphStructure(
-                "Not all weight-to-neuron edges have been processed, which "
-                "should never happen. " + default_invalid_structure_string
+                "Not all weight-to-neuron edges have been processed. "
+                + default_invalid_structure_string
             )