add custom exceptions

tests/test_err_msg.py

@@ -0,0 +1,23 @@
+import dataclasses
+
+import pytest
+
+import znflow
+
+
+@dataclasses.dataclass
+class ComputeMean(znflow.Node):
+    x: float
+    y: float
+
+    results: float = None
+
+    def run(self):
+        self.results = (self.x + self.y) / 2
+
+
+def test_attribute_access():
+    with znflow.DiGraph():
+        n1 = ComputeMean(2, 8)
+        with pytest.raises(znflow.exceptions.ConnectionAttributeError):
+            n1.x.data

znflow/__init__.py

@@ -4,6 +4,7 @@
 import logging
 import sys
 
+from znflow import exceptions
 from znflow.base import (
     CombinedConnections,
     Connection,
@@ -31,6 +32,7 @@
     "Property",
     "CombinedConnections",
     "combine",
+    "exceptions",
 ]
 
 with contextlib.suppress(ImportError):

znflow/base.py

@@ -3,8 +3,11 @@
 import contextlib
 import dataclasses
 import typing
+from typing import Any
 from uuid import UUID
 
+from znflow import exceptions
+
 
 @contextlib.contextmanager
 def disable_graph(*args, **kwargs):
@@ -183,6 +186,14 @@ def result(self):
             result = self.instance
         return result[self.item] if self.item else result
 
+    def __getattribute__(self, __name: str) -> Any:
+        try:
+            return super().__getattribute__(__name)
+        except AttributeError as e:
+            raise exceptions.ConnectionAttributeError(
+                "Connection does not support further attributes to its result."
+            ) from e
+
 
 @dataclasses.dataclass(frozen=True)
 class CombinedConnections:

znflow/exceptions.py

@@ -0,0 +1,5 @@
+"""ZnFlow exceptions."""
+
+
+class ConnectionAttributeError(AttributeError):
+    """Raised when a connection attribute is not found."""