Created attachment 1745041 [details]
segfault from RHEL 8 test system illustrating the issue

Description of problem:
After calling the .close() method on a PrimaryXmlFile or PrimarySqlite object, calling __repr__ or __str__ results in a coredump

Version-Release number of selected component (if applicable):
createrepo_c-libs-0.15.11-2.el8.x86_64
python3-createrepo_c-0.15.11-2.el8.x86_64

Issue appears to be present in every release across 7 and 8.

How reproducible:
Always

Steps to Reproduce:
Example 1:
# python3 -c 'import createrepo_c; p = createrepo_c.PrimarySqlite("primary.sqlite"); p.close(); p.__str__()'
Segmentation fault (core dumped)

Example 2:
# python3 -c 'import createrepo_c; p = createrepo_c.PrimarySqlite("primary.sqlite"); p.close(); p.__repr__()'
Segmentation fault (core dumped)

Example 3:
# python3 -c 'import createrepo_c; p = createrepo_c.PrimaryXmlFile("primary.xml"); p.close(); p.__str__()'
Segmentation fault (core dumped)

Example 4:
# python3 -c 'import createrepo_c; p = createrepo_c.PrimaryXmlFile("primary.xml"); p.close(); p.__repr__()'
Segmentation fault (core dumped)

Actual results:
Segfault

Expected results:
After closing, the object should still be available to be read, as is standard for other python modules. For example:

# python -c 'p = open("items.xml"); p.close(); print(p.__str__())'
<_io.TextIOWrapper name='items.xml' mode='r' encoding='UTF-8'>

Additional info:
Looking around it appears that other methods that are fully implemented via this library go through a check to see if the object was already closed. They go through check_XmlFileStatus():

static int
check_XmlFileStatus(const _XmlFileObject *self)
{
    assert(self != NULL);
    assert(XmlFileObject_Check(self));
    if (self->xmlfile == NULL) {
        PyErr_SetString(CrErr_Exception,
            "Improper createrepo_c XmlFile object (Already closed file?).");
        return -1;
    }
    return 0;
}

However, the __repr__ and __str__ do not. This results in a segfault when they try to access the object which is NULL after having been closed.