[ROS2] ModuleNotFoundError: No module named

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from the examples of ROS 2 I tried to copy the AddTwoInts Example to my own package. ros2 run try_srv add_two_ints_server generates an error when importing AddTwoInts

ModuleNotFoundError: No module named 'try_srv'

thought the reason is that the idl file is not generated (can't find them in install or build folder).

Changing from try_srv.srv import AddTwoInts back to from example_interfaces.srv import AddTwoInts works fine

this is the folder structure

this is the package file

<?xml version="1.0"?>
<?xml-model href="http://download.ros.org/schema/package_format2.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
<package format="3">
  <name>try_srv</name>
  <version>0.0.1</version>
  <description>migrated from examples</description>

  <license>Apache License 2.0</license>

  <buildtool_depend>rosidl_default_generators</buildtool_depend>

  <exec_depend>rclpy</exec_depend>
  <exec_depend>std_msgs</exec_depend>

  <member_of_group>rosidl_interface_packages</member_of_group>

  <export>
    <build_type>ament_python</build_type>
  </export>
</package>

is the folder and package.xml structure ok ?

if so what else could be the reason that the import fails ?