Add Header event notification system

[saimn]

From @embray on May 20, 2013 20:19

It would be endlessly useful if headers had an event notification subscription system. Any change on a header such as an addition of a keyword, a removal of a keyword, a change in value, a change in comment, etc. should publish an event to any and all subscribed listeners. Listeners should probably be stored on the Header instance as weakrefs to avoid reference cycles and various sorts of zombism.

Such a system would have a great many uses and would be very helpful for maintaining internal consistency of FITS files.

Copied from original issue: spacetelescope/PyFITS#14

[sushobhana]

hi @saimn i came across this issue and find it interesting...Any suggestion how to implement or proceed? Will it be looking for changes all the time?By publishing an event , should we denote the changes too?(or just the occuring of event) and what should the interface look like??
I am trying to learn!! Ignore if you are busy.

[saimn]

@sushobhana - I don't have more hints than what's in the issue description (migrated from the old PyFITS repository). The description gives is pretty good idea but this probably requires some knowledge of the fits.header code. There are easier issue to start with contributing ;)

[sushobhana]

@saimn OK.Thanks!