get_absolute_location can raise NoLocationError (#338)

Author: rickwierenga

Diff for: CHANGELOG.md

@@ -58,6 +58,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
   - get_direction -> pickup_direction
   - put_direction -> drop_direction
 - `location` parameter of `assign_child_resource` is not optional (https://github.com/PyLabRobot/pylabrobot/pull/336)
+- `Resource.get_absolute_location` raises `NoLocationError` instead of `AssertionError` when absolute location is not defined (https://github.com/PyLabRobot/pylabrobot/pull/338)
 
 ### Added
 

Diff for: pylabrobot/resources/errors.py

@@ -44,3 +44,9 @@ def __init__(self, resource_name: str):
       "Please create a PR to complete this resource, or create an issue if you "
       "need help. https://github.com/PyLabRobot/pylabrobot"
     )
+
+
+class NoLocationError(Exception):
+  """Raised when trying to access a location that does not exist, eg. when calling
+  get_absolute_location on a resource where some resource between it and the root
+  has no location."""

Diff for: pylabrobot/resources/resource.py

@@ -11,7 +11,7 @@
 from pylabrobot.utils.object_parsing import find_subclass
 
 from .coordinate import Coordinate
-from .errors import ResourceNotFoundError
+from .errors import NoLocationError, ResourceNotFoundError
 from .rotation import Rotation
 
 if sys.version_info >= (3, 11):
@@ -212,7 +212,8 @@ def get_absolute_location(self, x: str = "l", y: str = "f", z: str = "b") -> Coo
       z: `"t"`/`"top"`, `"c"`/`"center"`, or `"b"`/`"bottom"`
     """
 
-    assert self.location is not None, f"Resource {self.name} has no location."
+    if self.location is None:
+      raise NoLocationError(f"Resource {self.name} has no location.")
 
     rotated_anchor = Coordinate(
       *matrix_vector_multiply_3x3(