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Andrew, I do admit that I have a lot to learn about Unicode support in Python, for instance with its error-handling and its corner cases.
On Windows Vista, I do see that print() behaves differently than evaluating the expression. An exception is raised for:
 print('\N{GOTHIC LETTER AHSA}')
On Linux, I see the character print as ? in xterm and as a '?' when evaluated. In gnome-terminal (Ubuntu Mono font) it prints as a box containing the code point in hex. No exception is raised.
I do see your point. The patch I provided always substitutes the unsupported character with its full expansion. Returning to a point earlier raised by Martin, using REPLACEMENT CHARACTER instead would be better. It would make the behavior of IDLE more consistent with xterm and gnome-terminal, although it would cause IDLE to hide errors if the program ran from a Windows console instead of IDLE. 
Given that Windows and Linux (Ubuntu) behave differently, I'd rather let IDLE mimic the behavior of a Linux console than a Windows console.