Lets say there are operators (buttons .etc) that run or save the text in Text Editor. I need to change the text before such operators execute.

Is there a way involving some callback functions, listeners or handlers?

If there is not, is there a way to remove UI element and replace it in the same spot with custom operator? I only found a way how to append or prepend an operator to such menu or header.


1 Answer 1


I don't think that there are listeners which you can use in that way.

But what you can do is your idea in the second question. You could replace the button with a custom operator which executes your code first and calls the original operator afterwards. You can access the sources if you right-click on that original button and choose edit source. After that go to the scripting view and choose the source file available in the dropdown box

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  • $\begingroup$ I cant change the source code, this must work from addon. So I can only change it like: bpy.types.TEXT_HT_header.prepend(foo). The difficult part is to remove the old entry and place a new one in that spot. $\endgroup$ Commented Dec 4, 2014 at 11:55
  • $\begingroup$ Can you re-register the same operator to override its function? Although, then you'd have to do the work of that operator yourself. $\endgroup$
    – Mike Pan
    Commented Dec 5, 2014 at 1:38
  • 1
    $\begingroup$ Yeah I can re-register those classes in addon but that would be super dirty, there must be a cleaner way. I can't believe that there is no callback or anything in something such important as operators. Half of blender stands on them.. $\endgroup$ Commented Dec 5, 2014 at 21:08

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