Apparently, the list of allowed file formats to attach got shorter recently:

<type 'exceptions.ImportError'>: Attaching of '/home/malb/foobar.pyx'
not implemented (load .py, .spyx, and .sage files)

but attach 'foobar.spyx' works.

Component: user interface

Issue created by migration from https://trac.sagemath.org/ticket/414