Re-using copyrighted code

[Malte Forkel]

I have asked the PSF for help regarding the implications of the license
status of code from sre_parse.py and the missing  license statement in
sre.py. I'll happily report their answer to the list I they don't reply
in this thread.

At least partially, my confusion seems to be caused by the dichotomy of
the concepts of copyright and license. How do these relate to each other?

I understand that I have to pick a license for my package. And may be
I'm not free to pick any open source license due the license used by
Secret Labs AB. But how does that relate to the copyright statements?
Should I put my own copyright line in every source file in the package?
How about the file that re-uses portions of sre_parse.py? Can there or
should there be two copyright lines in that file, one from Secret Labs,
one my own?

Malte