why say.py in sound_play package cannot be used with roslaunch?

edit

say.py works if it come with rosrun. I mean at first I have launched a launch file containing:

<launch>

<node pkg="sound_play" type="soundplay_node.py" name="sound_play" output="screen"/>

</launch>

(consider its name is first.launch)

and then in another terminal I have run:

rosrun mypackage say.py

but how can I launch say.py with a launch file? I have say.py inside "mypackage" and a launch file(named second.launch) like this:

<launch>

<node pkg="mypackage" type="say.py" name="say" output="screen"/>

</launch>

but it got some errors in the terminal in which i have launched first.luanch:

sound: -3 command: 1 volume: 1.0 arg: __name:=say arg2: __log:=/home/mostafa/.ros/log/53b70204-7c11-11e7-b929-acbc32787137/say-1.log SIOD ERROR: unbound variable : __log:=/home/mostafa/.ros/log/53b70204-7c11-11e7-b929-acbc32787137/say-1.log

and a warning in the terminal of second.launch:

Saying: __name:=say Voice: __log:=/home/mostafa/.ros/log/53b70204-7c11-11e7-b929-acbc32787137/say-1.log Volume: 1.0