Add parameter substitution

launch_ros/launch_ros/actions/set_parameter.py

@@ -76,12 +76,12 @@ def parse(cls, entity: Entity, parser: Parser):
     @property
     def name(self) -> ParameterName:
         """Getter for name."""
-        return self.__param_dict.keys()[0]
+        return list(self.__param_dict.keys())[0]
 
     @property
     def value(self) -> ParameterValue:
         """Getter for value."""
-        return self.__param_dict.values()[0]
+        return list(self.__param_dict.values())[0]
 
     def execute(self, context: LaunchContext):
         """Execute the action."""

launch_ros/launch_ros/substitutions/__init__.py

@@ -18,11 +18,13 @@
 from .find_package import FindPackage
 from .find_package import FindPackagePrefix
 from .find_package import FindPackageShare
+from .parameter import Parameter
 
 
 __all__ = [
     'ExecutableInPackage',
     'FindPackage',
     'FindPackagePrefix',
     'FindPackageShare',
+    'Parameter',
 ]

launch_ros/launch_ros/substitutions/parameter.py

@@ -0,0 +1,72 @@
+# Copyright 2022 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module for the Parameter substitution."""
+
+from typing import Iterable
+from typing import List
+from typing import Text
+
+from launch.frontend import expose_substitution
+from launch.launch_context import LaunchContext
+from launch.some_substitutions_type import SomeSubstitutionsType
+from launch.substitution import Substitution
+from launch.substitutions.substitution_failure import SubstitutionFailure
+from launch.utilities import normalize_to_list_of_substitutions
+from launch.utilities import perform_substitutions
+
+
+@expose_substitution('param')
+class Parameter(Substitution):
+    """
+    Substitution that tries to get a parameter that was set by SetParameter.
+
+    :raise: SubstitutionFailure when param is not found
+    """
+
+    def __init__(
+        self,
+        name: SomeSubstitutionsType,
+    ) -> None:
+        """Create a Parameter substitution."""
+        super().__init__()
+        self.__name = normalize_to_list_of_substitutions(name)
+
+    @classmethod
+    def parse(cls, data: Iterable[SomeSubstitutionsType]):
+        """Parse a Parameter substitution."""
+        if not data or len(data) != 1:
+            raise AttributeError('param substitutions expect 1 argument')
+        kwargs = {'name': data[0]}
+        return cls, kwargs
+
+    @property
+    def name(self) -> List[Substitution]:
+        """Getter for name."""
+        return self.__name
+
+    def describe(self) -> Text:
+        """Return a description of this substitution as a string."""
+        name_str = ' + '.join([sub.describe() for sub in self.name])
+        return '{}(name={})'.format(self.__class__.__name__, name_str)
+
+    def perform(self, context: LaunchContext) -> Text:
+        """Perform the substitution."""
+        name = perform_substitutions(context, self.name)
+        params_container = context.launch_configurations.get('global_params', None)
+        for param in params_container:
+            if isinstance(param, tuple):
+                if param[0] == name:
+                    return param[1]
+        raise SubstitutionFailure("parameter '{}' not found".format(name))

test_launch_ros/test/test_launch_ros/frontend/test_parameter_substitution_frontend.py

@@ -0,0 +1,67 @@
+# Copyright 2022 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import io
+import textwrap
+
+from launch import LaunchService
+from launch.frontend import Parser
+from launch.utilities import perform_substitutions
+
+
+def test_parameter_substitution_yaml():
+    yaml_file = textwrap.dedent(
+        r"""
+        launch:
+            - set_parameter:
+                name: name
+                value: value
+
+            - let:
+                name: result
+                value: $(param name)
+        """
+    )
+    with io.StringIO(yaml_file) as f:
+        check_parameter_substitution(f)
+
+
+def test_parameter_substitution_xml():
+    xml_file = textwrap.dedent(
+        r"""
+        <launch>
+            <set_parameter name="name" value="value" />
+            <let name="result" value="$(param name)" />
+        </launch>
+        """
+    )
+    with io.StringIO(xml_file) as f:
+        check_parameter_substitution(f)
+
+
+def check_parameter_substitution(file):
+    root_entity, parser = Parser.load(file)
+    ld = parser.parse_description(root_entity)
+    ls = LaunchService()
+    ls.include_launch_description(ld)
+    assert 0 == ls.run()
+
+    def perform(substitution):
+        return perform_substitutions(ls.context, substitution)
+
+    set_parameter, let = ld.describe_sub_entities()
+    assert perform(set_parameter.name) == 'name'
+    assert perform(set_parameter.value) == 'value'
+    assert perform(let.name) == 'result'
+    assert perform(let.value) == 'value'

test_launch_ros/test/test_launch_ros/substitutions/test_parameter_substitution.py

@@ -0,0 +1,26 @@
+# Copyright 2022 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Test for the Parameter substitutions."""
+
+from launch import LaunchContext
+
+from launch_ros.actions import SetParameter
+from launch_ros.substitutions import Parameter
+
+
+def test_parameter_substitution():
+    context = LaunchContext()
+    SetParameter('name', 'value').execute(context)
+    assert Parameter('name').perform(context) == 'value'