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Speaking entirely from a point of ignorance, why are the source line #s not shown for frames that are implemented in modules loaded from zipimport?

Because the code printing the tracebacks doesn't know how to look inside a zip file.

Maybe, if the source file can't be found, it could decompile the bytecode?

Too clever by far. The peculiar way in which the comments disappear, the fact that the code is wrong when I used a (so-far-non-existent) peephole optimizer to optimize my .pyc files... I'd rather show NO line (so long as we still give file and line number) than try to guess in an overly clever manner. -- Michael Chermside