Attached is a patch which adds linenumbering to IDLE. [1] is the current discussion regarding this topic at idle-dev.

This patch is a initial patch. It is missing menu and config additions. I have posted it in this state, so that we can catch platform specific bugs and performance related issues(if any). In the patch, all major additions are in a new file LineNumber.py. This is keeping easier debugging in mind. The code will be restructured in the next version of the patch, which will have the above said additions and performance optimization(if any).

I will be working on menu additions, config dialog additions and performance optimization in the mean time.

For those who are interested, I used tk.call(self.text, 'dlineinfo', '%d.0' % linenum) instead of text.dlineinfo('%d.0' % linenum), because using any text.* method, used to cause a continuous increase in memory usage. I found this out the hard way, when, earlier I was making repeated text.index() calls.

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[1] - https://mail.python.org/pipermail/idle-dev/2014-June/003456.html