Using get_parameter_or in rclpy modules to prevent spurious exceptions.

- Minor doc improvements.

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

rclpy/rclpy/node.py

@@ -328,24 +328,29 @@ def get_parameter(self, name: str) -> Parameter:
         else:
             raise ParameterNotDeclaredException()
 
-    def get_parameter_or(self, name: str, alternative_value: Parameter) -> Parameter:
+    def get_parameter_or(self, name: str, alternative_value: Parameter = None) -> Parameter:
         """
         Get a parameter or the alternative value.
 
+        If the alternative value is None, a default Parameter with the given name and NOT_SET
+        type will be returned.
         This method does not declare parameters in any case.
 
         :param name: Name of the parameter to get.
         :param alternative_value: Alternative parameter to get if it had not been declared before.
         :return: Requested parameter, or alternative value if it hadn't been declared before.
         """
+        if alternative_value is None:
+            alternative_value = Parameter(name, Parameter.Type.NOT_SET)
+
         return self._parameters.get(name, alternative_value)
 
     def set_parameters(self, parameter_list: List[Parameter]) -> List[SetParametersResult]:
         """
         Set parameters for the node, and return the result for the set action.
 
         If any parameter in the list was not declared beforehand and undeclared parameters are not
-        allowed for the node, this function will raise a ParameterNotDeclaredException exception.
+        allowed for the node, this method will raise a ParameterNotDeclaredException exception.
 
         Parameters are set in the order they are declared in the list.
         If setting a parameter fails due to not being declared, then the
@@ -381,7 +386,7 @@ def _set_parameters(
         """
         Set parameters for the node, and return the result for the set action.
 
-        Method for internal usage; applies a setter function for each parameters in the list.
+        Method for internal usage; applies a setter method for each parameters in the list.
         By default it doesn't check if the parameters were declared, and both declares and sets
         the given list.
 
@@ -415,7 +420,7 @@ def set_parameters_atomically(self, parameter_list: List[Parameter]) -> SetParam
         Set the given parameters, all at one time, and then aggregate result.
 
         If any parameter in the list was not declared beforehand and undeclared parameters are not
-        allowed for the node, this function will raise a ParameterNotDeclaredException exception.
+        allowed for the node, this method will raise a ParameterNotDeclaredException exception.
 
         Parameters are set all at once. If setting a parameter fails due to not being declared,
         then no parameter will be set set. Either all of the parameters are set or none of them
@@ -484,7 +489,7 @@ def _set_parameters_atomically(self, parameter_list: List[Parameter]) -> SetPara
                 parameter_event.node = self.get_namespace() + '/' + self.get_name()
             for param in parameter_list:
                 if Parameter.Type.NOT_SET == param.type_:
-                    if Parameter.Type.NOT_SET != self.get_parameter(param.name).type_:
+                    if Parameter.Type.NOT_SET != self.get_parameter_or(param.name).type_:
                         # Parameter deleted. (Parameter had value and new value is not set)
                         parameter_event.deleted_parameters.append(
                             param.to_parameter_msg())
@@ -493,7 +498,7 @@ def _set_parameters_atomically(self, parameter_list: List[Parameter]) -> SetPara
                     if param.name in self._parameters:
                         del self._parameters[param.name]
                 else:
-                    if Parameter.Type.NOT_SET == self.get_parameter(param.name).type_:
+                    if Parameter.Type.NOT_SET == self.get_parameter_or(param.name).type_:
                         #  Parameter is new. (Parameter had no value and new value is set)
                         parameter_event.new_parameters.append(param.to_parameter_msg())
                     else:

rclpy/rclpy/parameter_service.py

@@ -62,19 +62,19 @@ def __init__(self, node):
 
     def _describe_parameters_callback(self, request, response):
         for name in request.names:
-            p = self._node.get_parameter(name)
+            p = self._node.get_parameter_or(name)
             response.descriptors.append(p.descriptor)
         return response
 
     def _get_parameters_callback(self, request, response):
         for name in request.names:
-            p = self._node.get_parameter(name)
+            p = self._node.get_parameter_or(name)
             response.values.append(p.get_parameter_value())
         return response
 
     def _get_parameter_types_callback(self, request, response):
         for name in request.names:
-            response.types.append(self._node.get_parameter(name).type_)
+            response.types.append(self._node.get_parameter_or(name).type_)
         return response
 
     def _list_parameters_callback(self, request, response):

rclpy/rclpy/time_source.py

@@ -69,7 +69,7 @@ def attach_node(self, node):
             self.detach_node()
         self._node = node
 
-        use_sim_time_param = node.get_parameter('use_sim_time')
+        use_sim_time_param = node.get_parameter_or('use_sim_time')
         if use_sim_time_param.type_ != Parameter.Type.NOT_SET:
             if use_sim_time_param.type_ == Parameter.Type.BOOL:
                 self.ros_time_is_active = use_sim_time_param.value