calibre requires python3-tzlocal to run, but does not have it as a dependency. 

running calibre without python3-tzlocal throws:
ModuleNotFoundError: No module named 'tzlocal'


example:

$ sudo dnf reinstall calibre # everything is properly set up
Updating and loading repositories:
Repositories loaded.
Package                                Arch       Version                                Repository                Size
Reinstalling:
 calibre                               x86_64     0:9.8.0-1.fc44                         updates               62.0 MiB
   replacing calibre                   x86_64     0:9.8.0-1.fc44                         updates               62.0 MiB

Transaction Summary:
 Reinstalling:       1 package
 Replacing:          1 package

Total size of inbound packages is 28 MiB. Need to download 28 MiB.
After this operation, 0 B extra will be used (install 62 MiB, remove 62 MiB).
Is this ok [y/N]: y
[1/1] calibre-0:9.8.0-1.fc44.x86_64                                            100% |   8.4 MiB/s |  27.8 MiB |  00m03s
-----------------------------------------------------------------------------------------------------------------------
[1/1] Total                                                                    100% |   7.5 MiB/s |  27.8 MiB |  00m04s
Running transaction
[1/4] Verify package files                                                     100% |   8.0   B/s |   1.0   B |  00m00s
[2/4] Prepare transaction                                                      100% |   2.0   B/s |   2.0   B |  00m01s
[3/4] Reinstalling calibre-0:9.8.0-1.fc44.x86_64                               100% |  63.9 MiB/s |  62.4 MiB |  00m01s
[4/4] Removing calibre-0:9.8.0-1.fc44.x86_64                                   100% | 499.0   B/s |   2.3 KiB |  00m05s
Complete!

$ calibre
Traceback (most recent call last):
  File "/usr/bin/calibre", line 21, in <module>
    sys.exit(calibre())
             ~~~~~~~^^
  File "/usr/lib64/calibre/calibre/gui_launch.py", line 72, in calibre
    from calibre.gui2.main import main
  File "/usr/lib64/calibre/calibre/gui2/__init__.py", line 88, in <module>
    from calibre.utils.date import UNDEFINED_DATE
  File "/usr/lib64/calibre/calibre/utils/date.py", line 14, in <module>
    from calibre.utils.iso8601 import UNDEFINED_DATE, local_tz, utc_tz
  File "/usr/lib64/calibre/calibre/utils/iso8601.py", line 8, in <module>
    import tzlocal
ModuleNotFoundError: No module named 'tzlocal'

1 $ sudo dnf in python3-tzlocal
Updating and loading repositories:
Repositories loaded.
Package                                Arch       Version                                Repository                Size
Installing:
 python3-tzlocal                       noarch     0:5.3.1-6.fc44                         fedora               125.3 KiB

Transaction Summary:
 Installing:         1 package

Total size of inbound packages is 52 KiB. Need to download 52 KiB.
After this operation, 125 KiB extra will be used (install 125 KiB, remove 0 B).
Is this ok [y/N]: y
[1/1] python3-tzlocal-0:5.3.1-6.fc44.noarch                                    100% | 298.8 KiB/s |  52.3 KiB |  00m00s
-----------------------------------------------------------------------------------------------------------------------
[1/1] Total                                                                    100% |  71.1 KiB/s |  52.3 KiB |  00m01s
Running transaction
[1/3] Verify package files                                                     100% | 166.0   B/s |   1.0   B |  00m00s
[2/3] Prepare transaction                                                      100% |   2.0   B/s |   1.0   B |  00m00s
[3/3] Installing python3-tzlocal-0:5.3.1-6.fc44.noarch                         100% | 198.7 KiB/s | 130.3 KiB |  00m01s
Complete!

$ calibre # ran successfully

$

Reproducible: Always

Steps to Reproduce:
1. Install calibre, without installing python3-tzlocal
2. Run calibre

Actual Results:
python throws ModuleNotFoundError: No module named 'tzlocal'

Expected Results:
calibre should launch normally