You bring up a good point. I am currently trying to teach myself Python with PyQt4 and my goal is to write my own basic editor for the sake of learning.
One of the reasons I decided to try writing an editor is because while I've found some editor's that I can work in I wouldn't say I've been really satisfied with what I've used. There are already some full featured open source editor/IDE's written in Python which I intend to refer to once I have a better understanding of it so that I can try and learn from what other people have done as well.
However this isn't really the best advice for someone that is already working on another project as it will take time away from current development. Of course if a person is already good with Python perhaps they can get a descent app written in a weekend like you suggested.