Using NaN constants in message/service definitions

edit

As part of implementing a simulator, I have a service used for resetting the simulator states named ResetState. To be able to reset only some states, I have defined a constant (float64, NaN) in the service definition which can be used to mark states which should not be reset. See the service definition:

# Service for resetting simulator states. States set to ResetState.KEEP is not reset

float64 KEEP=NaN  # Used for specifying states not to change

float64 north
float64 east
float64 heading
float64 surge_speed
float64 sway_speed
float64 yaw_rate
float64 a_1
float64 w_1
float64 a_2
float64 w_2
---
bool success

I am able to build the workspace just fine, but when I try to load the service in Python I get NameError: name 'nan' is not defined.

This is not surprising when looking at the generated code, which attempts to use the nan keyword without importing it (e.g. by from numpy import nan):

# This Python file uses the following encoding: utf-8
"""autogenerated by genpy from sim_milliampere/ResetStateRequest.msg. Do not edit."""
import sys
python3 = True if sys.hexversion > 0x03000000 else False
import genpy
import struct


class ResetStateRequest(genpy.Message):
  _md5sum = "42225d3d73aa534da7b187c737de1988"
  _type = "sim_milliampere/ResetStateRequest"
  _has_header = False #flag to mark the presence of a Header object
  _full_text = """

float64 KEEP=NaN

float64 north
float64 east
float64 heading
float64 surge_speed
float64 sway_speed
float64 yaw_rate
float64 a_1
float64 w_1
float64 a_2
float64 w_2
"""
  # Pseudo-constants
  KEEP = nan

  __slots__ = ['north','east','heading','surge_speed','sway_speed','yaw_rate','a_1','w_1','a_2','w_2']
  _slot_types = ['float64','float64','float64','float64','float64','float64','float64','float64','float64','float64']

Is there a way to make catkin_make include the required import (e.g. from numpy import nan) in the generated code? I tried adding python-numpy as exec_depend and build-depend in package.xml without it solving the problem.

I'm using ROS Kinetic on Ubuntu 16.04 5.3.0-40-generic.