Reproduce the bug with builds:
nbdkit-1.2.6-1.el7_6.1.x86_64
nbdkit-plugin-python2-1.2.6-1.el7_6.1.x86_64
nbdkit-plugin-python-common-1.2.6-1.el7_6.1.x86_64

Reproduce steps:
1.Create a file called 'test.py' containing:

$ cat test.py 
def function():
    raise RuntimeError("error")
def config(key, value):
    function()
def open(readonly):
    raise RuntimeError("open")
def get_size(h):
    raise RuntimeError("get_size")
def pread(h, count, offset):
    raise RuntimeError("pread")

2.Run command:
$ nbdkit -fv python2 ./test.py foo=bar
nbdkit: debug: TLS disabled: could not load TLS certificates
nbdkit: debug: registering plugin /usr/lib64/nbdkit/plugins/nbdkit-python2-plugin.so
nbdkit: debug: registered plugin /usr/lib64/nbdkit/plugins/nbdkit-python2-plugin.so (name python)
nbdkit: debug: python: load
nbdkit: debug: python: config key=script, value=./test.py
nbdkit: debug: python: config key=foo, value=bar
nbdkit: error: ./test.py: config: error: error


Verify the bug with latest builds:
nbdkit-1.2.6-1.el7_6.2.x86_64
nbdkit-plugin-python2-1.2.6-1.el7_6.2.x86_64
nbdkit-plugin-python-common-1.2.6-1.el7_6.2.x86_64

Steps:
1.Execute the command of reproduce step2 again
$ nbdkit -fv python2 ./test.py foo=bar
nbdkit: debug: TLS disabled: could not load TLS certificates
nbdkit: debug: registering plugin /usr/lib64/nbdkit/plugins/nbdkit-python2-plugin.so
nbdkit: debug: registered plugin /usr/lib64/nbdkit/plugins/nbdkit-python2-plugin.so (name python)
nbdkit: debug: python: load
nbdkit: debug: python: config key=script, value=./test.py
nbdkit: debug: python: config key=foo, value=bar
nbdkit: error: ./test.py: config: error: ['Traceback (most recent call last):\n', '  File "./test.py", line 4, in config\n    function()\n', '  File "./test.py", line 2, in function\n    raise RuntimeError("error")\n', 'RuntimeError: error\n']


Result:
   After updating nbdkit, we can get full traceback when a Python call fails, so move the bug from ON_QA to VERIFIED

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2018:3658