TOPCAT and Python

Reading time ~2 minutes

In this post I’m going to give some very basic examples on how to get Python and TOPCAT (or other VO/SAMP applications) to talk to each other. The Python module you’ll need is called SAMPy. This module will eventually be incorporated into the AstroPy package. To install SAMPy:

pip install sampy

(or if you must, use easy_install sampy)

For our first example we’ll get TOPCAT to notify Python when we highlight a point or row in TOPCAT:

""" Interact with TOPCAT via SAMPy at the most basic level """

import sampy

if __name__ == "__main__":

    # The 'Hub' is for multiple applications to talk to each other.
    hub = sampy.SAMPHubServer()

    # We need a client that will connect to the Hub. TOPCAT will also
    # connect to our Hub.
    client = sampy.SAMPIntegratedClient(metadata={
        "": "topdog",
        "samp.description.text": "Live demos are destined for disaster."

    # Create a 'callback' - something to do when a point or row is highlighted in TOPCAT
    def receive_samp_notification(private_key, sender_id, mtype, params, extra):
        print("Notification of {0} from {0} ({1}): {2}, {3}".format(mtype, sender_id, private_key, params, extra))

    # Register the callback
    client.bindReceiveNotification("table.highlight.row", receive_samp_notification)


  1. Run the above code by putting it in a file named then from the terminal write: python

  2. Open TOPCAT and load a file. Ensure there are 3 icons in the SAMP Clients tab at the bottom of the TOPCAT GUI.

  3. In the “Current Table Properties”, make sure the “Broadcast Row” icon is ticked.

  4. Highlight a row and look at the Python output:

In [1]: run -i
[SAMP] Info    (2013-12-10T16:01:45.882344): Hub started

In [2]: 
Notification of table.highlight.row from table.highlight.row (cli#3): 5338b24be010f6ca598c744f3eea3afc, {'url': 'file:/Users/andycasey/thesis/presentations/2013/2013-csiro-astro/data/fld_list_230611', 'row': '4'}

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