Comment 4 for bug 1661682

Workaround: $ sudo apt install python-gi
After installing python-gi the light-locker-settings starts without issues.
I think there is a missing dependency from package light-locker-settings to python-gi.
Adding this dependency should fix this issue.

$ apt-cache policy light-locker-settings
light-locker-settings:
  Installiert: 1.5.0-0ubuntu2
  Installationskandidat: 1.5.0-0ubuntu2
  Versionstabelle:
 *** 1.5.0-0ubuntu2 500
        500 http://de.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
        100 /var/lib/dpkg/status

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.4 LTS
Release: 18.04
Codename: bionic

$ inxi -bz
System: Host: idefix Kernel: 4.15.0-96-generic x86_64 bits: 64 Desktop: Xfce 4.12.3
           Distro: Ubuntu 18.04.4 LTS
Machine: Device: laptop System: Acer product: AOD270 v: V1.10 serial: N/A
           Mobo: Acer model: JE01_CT serial: N/A BIOS: Insyde v: V1.10 date: 07/23/2013
Battery BAT1: charge: 18.7 Wh 100.0% condition: 18.7/48.8 Wh (38%)
CPU: Dual core Intel Atom N2600 (-MT-MCP-) speed/max: 816/1600 MHz
Graphics: Card: Intel Atom Processor D2xxx/N2xxx Integrated Graphics Controller
           Display Server: x11 (X.Org 1.19.6 ) drivers: modesetting (unloaded: fbdev,vesa)
           Resolution: 1024x600@60.03hz
           OpenGL: renderer: llvmpipe (LLVM 9.0, 128 bits) version: 3.3 Mesa 19.2.8
Network: Card-1: Realtek RTL810xE PCI Express Fast Ethernet controller driver: r8169
           Card-2: Broadcom and subsidiaries BCM4313 802.11bgn Wireless Network Adapter driver: wl
Drives: HDD Total Size: 320.1GB (2.8% used)
Info: Processes: 172 Uptime: 29 min Memory: 1061.6/1981.9MB Client: Shell (bash) inxi: 2.3.56