[AstroPy] new pyfits version deletes NP_pyfits, breaking pickle

[Joe Harrington]

My research group uses Python pickles to save data as it goes through
our pipeline (.npy and .npz do not save objects, and neither does HDF,
etc.).  These need to be loadable forever, as we often compare work to
work done much earlier.  Some of the objects we save contain pyfits
header objects.  Pickles have to import all classes used in the
pickled objects before they load, and we are getting an ImportError
about NP_pyfits.  The file NP_pyfits.py existed in stsci_python 2.8
but is gone in 2.10.  The pickles refer to this object explicitly:

....
sS'photchan'
p494
I3
sS'header'
p495
(ipyfits.NP_pyfits
Header
p496
(dp497
S'_hdutype'
p498
cpyfits.NP_pyfits
PrimaryHDU
p499
sS'ascard'
p500
ccopy_reg
_reconstructor
p501
(cpyfits.NP_pyfits
CardList
p502
c__builtin__
list
p503
(lp504
g501
(cpyfits.NP_pyfits
Card
p505
c__builtin__
object
p506
NtRp507
(dp508
S'_valuestring'
p509
S'T'
....

Is there any way to make our pickles readable again, other than
running the old version of pyfits forever?  Can you provide a pickle
converter that replaces the old names in the file with whatever is
new?

Please (everyone, not just STScI) be aware of this issue going
forward.  Pickles are the only way we know of to save objects.  You
can add things to your classes, but if you change what they import (or
otherwise break pickle), nobody can restore your class across
releases.

Thanks,

--jh--