Implementing methods related with ParameterDescriptors.

- Addressing minor comments on API.

Signed-off-by: Juan Ignacio Ubeira <jubeira@ekumenlabs.com>

rclpy/rclpy/exceptions.py

@@ -91,3 +91,9 @@ class InvalidParameterValueException(Exception):
 
     def __init__(self, *args):
         Exception.__init__(self, 'Invalid parameter value.', *args)
+
+class ParameterImmutableException(Exception):
+    """Raised when a read-only parameter is modified."""
+
+    def __init__(self, *args):
+        Exception.__init__(self, 'Attempted to modify an read-only parameter.', *args)

rclpy/rclpy/node.py

@@ -30,7 +30,11 @@
 from rclpy.clock import ROSClock
 from rclpy.constants import S_TO_NS
 from rclpy.context import Context
-from rclpy.exceptions import NotInitializedException, ParameterNotDeclaredException
+from rclpy.exceptions import InvalidParameterException
+from rclpy.exceptions import InvalidParameterValueException
+from rclpy.exceptions import NotInitializedException
+from rclpy.exceptions import ParameterAlreadyDeclaredException
+from rclpy.exceptions import ParameterNotDeclaredException
 from rclpy.executors import Executor
 from rclpy.expand_topic_name import expand_topic_name
 from rclpy.guard_condition import GuardCondition
@@ -283,7 +287,7 @@ def undeclare_parameter(self, name: str):
             raise ParameterNotDeclaredException()
 
     def has_parameter(self, name: str) -> bool:
-        """Returns true if parameter is declared; false otherwise."""
+        """Returns True if parameter is declared; False otherwise."""
         return name in self._parameters
 
     def get_parameters(self, names: List[str]) -> List[Parameter]:
@@ -315,10 +319,7 @@ def get_parameter_or(self, name: str, alternative_value: Parameter) -> Parameter
         :param name: Name of the parameter to get.
         :alternative_value: Alternative parameter to get if it had not been declared before.
         """
-        if has_parameter(name):
-            return self._parameters[name]
-        else:
-            return alternative_value
+        return self._parameters.get(name, alternative_value)
 
     def set_parameters(self, parameter_list: List[Parameter]) -> List[SetParametersResult]:
         """
@@ -454,10 +455,15 @@ def describe_parameter(self, name: str) -> ParameterDescriptor:
         :raises ParameterNotDeclaredException: if parameter had not been declared before
             and undeclared parameters are not allowed.
         """
-        # TODO(jubeira): Implement this method.
-        pass
+        try:
+            return self._parameters[name].descriptor
+        except KeyError e:
+            if self._allow_undeclared_parameters:
+                return ParameterDescriptor()
+            else:
+                raise ParameterNotDeclaredException()
 
-    def describe_parameters(self, name: List[str]) -> List[ParameterDescriptor]:
+    def describe_parameters(self, names: List[str]) -> List[ParameterDescriptor]:
         """
         Gets the parameter descriptors of a given list of parameters.
 
@@ -468,8 +474,11 @@ def describe_parameters(self, name: List[str]) -> List[ParameterDescriptor]:
         :raises ParameterNotDeclaredException: if at least one parameter
             had not been declared before and undeclared parameters are not allowed.
         """
-        # TODO(jubeira): Implement this method.
-        pass
+        parameter_descriptors = []
+        for name in names:
+            parameter_descriptors.append(self.describe_parameter(name))
+
+        return parameter_descriptors
 
     def set_parameters_callback(
         self,

rclpy/rclpy/parameter.py

@@ -86,8 +86,7 @@ def from_parameter_msg(cls, param_msg):
             value = param_msg.value.string_array_value
         return cls(param_msg.name, type_, value)
 
-    # TODO(jubeira): Add support for ParameterDescriptor.
-    def __init__(self, name, type_, value=None):
+    def __init__(self, name, type_, value=None, descriptor=ParameterDescriptor()):
         if not isinstance(type_, Parameter.Type):
             raise TypeError("type must be an instance of '{}'".format(repr(Parameter.Type)))
 
@@ -97,6 +96,9 @@ def __init__(self, name, type_, value=None):
         self._type_ = type_
         self._name = name
         self._value = value
+        descriptor.name = name
+        descriptor.value = value
+        self._descriptor = descriptor
 
     @property
     def name(self):
@@ -110,8 +112,9 @@ def type_(self):
     def value(self):
         return self._value
 
-    def get_descriptor(self):
-        return ParameterDescriptor(name=self.name, type=self.type_.value)
+    @property
+    def descriptor(self):
+        return self._descriptor
 
     def get_parameter_value(self):
         parameter_value = ParameterValue(type=self.type_.value)

rclpy/rclpy/parameter_service.py

@@ -63,7 +63,7 @@ def __init__(self, node):
     def _describe_parameters_callback(self, request, response):
         for name in request.names:
             p = self._node.get_parameter(name)
-            response.descriptors.append(p.get_descriptor())
+            response.descriptors.append(p.descriptor)
         return response
 
     def _get_parameters_callback(self, request, response):