Introduce PathsNotGreaterThanOneError (FV2310 E_0266) (#102)

Author: hf-kklein

src/ebdtable2graph/graph_utils.py

@@ -8,6 +8,7 @@
 from networkx import DiGraph, all_simple_paths  # type:ignore[import]
 
 from ebdtable2graph.models import ToNoEdge, ToYesEdge
+from ebdtable2graph.models.errors import PathsNotGreaterThanOneError
 
 COMMON_ANCESTOR_FIELD = "common_ancestor_for_node"
 # Defines the label to annotate the last common ancestor node with the information to which node
@@ -43,7 +44,12 @@ def _mark_last_common_ancestors(graph: DiGraph) -> None:
         if in_degree <= 1:
             continue
         paths = list(all_simple_paths(graph, source="Start", target=node))
-        assert len(paths) > 1, "If indegree > 1, the number of paths should always be greater than 1 too."
+        if len(paths) <= 1:
+            raise PathsNotGreaterThanOneError(
+                node_key=node,
+                indegree=in_degree,
+                number_of_paths=len(paths),
+            )
         common_ancestor = _find_last_common_ancestor(paths)
         assert common_ancestor != "Start", "Last common ancestor should always be at least the first decision node '1'."
         # Annotate the common ancestor for later conversion

src/ebdtable2graph/models/errors/__init__.py

@@ -21,3 +21,18 @@ def __init__(self, msg: str, decision_node_key, outgoing_edges: list[str]):
 
     def __str__(self):
         return f"The node {self.decision_node_key} has more than 2 outgoing edges: {', '.join(self.outgoing_edges)}"
+
+
+class PathsNotGreaterThanOneError(ValueError):
+    """
+    If indegree > 1, the number of paths should always be greater than 1 too.
+    Typically, this is a symptom for loops in the graph (which makes them not a Directed Graph / tree anymore).
+    """
+
+    def __init__(self, node_key: str, indegree: int, number_of_paths: int):
+        super().__init__(
+            f"The indegree of node '{node_key}' is {indegree} > 1, but the number of paths is {number_of_paths} <= 1."
+        )
+        self.node_key = node_key
+        self.indegree = indegree
+        self.number_of_paths = number_of_paths