Description of problem:

Calibre fails to start with error: AttributeError: 'NoneType' object has no attribute 'cancel'

Version-Release number of selected component (if applicable):

calibre-4.12.0-1.fc31.x86_64

How reproducible:

Each start attempt fails with this error.

Steps to Reproduce:
1. Call "calibre" from command-line.
2.
3.

Actual results:

$ calibre
Traceback (most recent call last):
  File "/usr/bin/calibre", line 20, in <module>
    sys.exit(calibre())
  File "/usr/lib64/calibre/calibre/gui_launch.py", line 72, in calibre
    main(args)
  File "/usr/lib64/calibre/calibre/gui2/main.py", line 542, in main
    listener = create_listener()
  File "/usr/lib64/calibre/calibre/gui2/main.py", line 513, in create_listener
    return Listener(address=gui_socket_address())
  File "/usr/lib64/calibre/calibre/utils/ipc/server.py", line 109, in __init__
    self._listener._unlink.cancel()
AttributeError: 'NoneType' object has no attribute 'cancel'


Expected results:

calibre GUI appears.

Additional info:

The problem arises after applying most recent python updates:

- python3-3.7.8-1.fc31.x86_64
- python3-libs-3.7.8-1.fc31.x86_64
- python-unversioned-command-3.7.8-1.fc31.noarch

After downgrading these packages calibre was operational again:

$ dnf downgrade python3-3.7.7-3.fc31.x86_64 python-unversioned-command-3.7.7-3.fc31.noarch python3-libs-3.7.7-3.fc31.x86_64