changed verify('fix') to verify('fix+warn') when printing fits cards - #5054

The behavior I was actually looking for is fix+warn, so the card is fixed if possible but an exception is not raised if it can't be fixed (which happens only when the header keyword is invalid). I fixed this in the most recent commit, and now it passes all the unit tests.

👍 on doing something for this issue (see also #3668, #887). cc @embray ;-)

We had again this issue recently with a FITS file containing an illegal 'IRAF-B/P'keyword. The first time I print the header it fails with a VerifyError, and the second time it is well printed (because the first time the problematic card has been "verified"). As a consequence fitsheader fails to print the header.

VerifyError: 
Verification reported errors:
Unfixable error: Illegal keyword name 'IRAF-B/P'
Note: PyFITS uses zero-based indexing.

Ideally the default behavior could be configurable ? Currently it is possible to change it only when writing a file.

The real problem here is deeper problems with the verification system that I've groaned about before, but don't have a clear solution to offer.

Part of the problem with this is that Card.image is not just used when printing, but also when writing to a physical file. So you need a solution that will allow invalid headers to at least be printable (which I agree should be possible) but that will not allow invalid FITS files to be written.

I think probably the call to self.verify should be moved out of the image property altogether. It's actually kind of bad when a property has side-effects (there are exceptions of course, and plenty of good exceptions even in io.fits, but this I think is not one of them).

I think there probably are reasons that verify() is called there, but maybe for whatever those reasons were maybe the verify() call should happen closer to the specific interfaces where it matters (e.g. printing, writing to a file, etc.)

Merging this one. If someone wants to revisit the deeper problems mentioned, it can be a new PR.