python expressions substitution include names of all parents for specified modules

launch/launch/substitutions/python_expression.py

@@ -105,7 +105,12 @@ def perform(self, context: LaunchContext) -> Text:
         """Perform the substitution by evaluating the expression."""
         from ..utilities import perform_substitutions
         module_names = [context.perform_substitution(sub) for sub in self.python_modules]
-        module_objects = [importlib.import_module(name) for name in module_names]
+        # Get names of package and all parents for modules in the list of python_modules
+        # For example, python module "a.b.c" has parents "a.b" and "a"
+        inherited_names = [".".join(p[0:n]) for n in range(1, len(p)) for p in
+                           [name.split('.') for name in module_names]]
+        all_module_names = list(set(module_names + inherited_names))
+        module_objects = [importlib.import_module(name) for name in all_module_names]
         expression_locals = {}
         for module in module_objects:
             # For backwards compatility, we allow math definitions to be implicitly

launch/test/launch/substitutions/test_python_expression.py

@@ -114,3 +114,27 @@ def test_python_substitution_two_modules():
     # Test the describe() method
     assert subst.describe() ==\
         "PythonExpr('math.isfinite(sys.getrefcount(str(\"hello world!\")))', ['sys', 'math'])"
+
+
+def test_python_substitution_submodule():
+    """Evaluation while passing modules within a package."""
+    python_modules = [
+        'launch.substitutions.PythonExpression',
+        'launch.substitutions.SubstitutionFailure',
+        'launch.utilities.is_a_subclass'
+    ]
+    lc = LaunchContext()
+    expr = (
+        f'not launch.utilities.is_a_subclass('
+        f'    launch.substitutions.PythonExpression,'
+        f'    launch.substitutions.SubstitutionFailure'
+        f')'
+    )
+    subst = PythonExpression([expr], python_modules)
+    try:
+        result = subst.perform(lc)
+    except SubstitutionFailure:
+        pytest.fail('Failed to evaluate PythonExpression containing sys module.')
+
+    # The expression should evaluate to True
+    assert result