Subscribe to Rostopic from flask app

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Hi,

I have Ros melodic installed in Ubuntu 18.04. I have a sample rosbag which have some rostopics. I have an existing flask app in which I need to subscribe to these topics and get the response as message objects and pass that to catkin package for further processing.

What I have done thus far is that in the flask app I used subprocess to trigger a listener script which subscribes to the topics. But the subprocess is not returning the message object.

p = subprocess.check_output(["./listener.py"])

When I run the listener in python shell , it executes correctly.

What I like to have is on calling the flask app, the listener script is executed and message object is returned back to flask app. Any suggestions will be much appreciated. Thanks.