No module named 'genmsg' during ROS installation in AarchLinux?

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Hi, I'm trying to install ROS on my Archlinux laptop and I get the following error?

:: Starting the build:
Running as unit: run-u4258.service
==> Making package: ros-melodic-std-srvs 1.11.2-2 (Sun 16 Feb 2020 22:22:06 CET)
==> Checking runtime dependencies...
error: could not register 'arch4edu' database (database already registered)
error: could not register 'arch4edu' database (database already registered)
error: could not register 'arch4edu' database (database already registered)
==> Checking buildtime dependencies...
error: could not register 'arch4edu' database (database already registered)
error: could not register 'arch4edu' database (database already registered)
error: could not register 'arch4edu' database (database already registered)
==> Retrieving sources...
  -> Downloading ros-melodic-std-srvs-1.11.2.tar.gz...
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   125    0   125    0     0    206      0 --:--:-- --:--:-- --:--:--   205
100  2482    0  2482    0     0   1864      0 --:--:--  0:00:01 --:--:--  1864
==> Validating source files with sha256sums...
    ros-melodic-std-srvs-1.11.2.tar.gz ... Passed
==> Extracting sources...
  -> Extracting ros-melodic-std-srvs-1.11.2.tar.gz with bsdtar
==> Starting build()...
-- The C compiler identification is GNU 9.2.1
-- The CXX compiler identification is GNU 9.2.1
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Using CATKIN_DEVEL_PREFIX: /var/cache/private/pikaur/build/ros-melodic-std-srvs/src/build/devel
-- Using CMAKE_PREFIX_PATH: /opt/ros/melodic
-- This workspace overlays: /opt/ros/melodic
-- Found PythonInterp: /usr/bin/python3 (found version "3.8.1")
-- Using PYTHON_EXECUTABLE: /usr/bin/python3
-- Using default Python package layout
-- Found PY_em: /usr/lib/python3.8/site-packages/em.py
-- Using empy: /usr/lib/python3.8/site-packages/em.py
-- Using CATKIN_ENABLE_TESTING: ON
-- Skip enable_testing() when building binary package
-- Using CATKIN_TEST_RESULTS_DIR: /var/cache/private/pikaur/build/ros-melodic-std-srvs/src/build/test_results
-- Found gtest: gtests will be built
-- Using Python nosetests: /usr/bin/nosetests-3.8
-- catkin 0.7.19
-- BUILD_SHARED_LIBS is on
-- Using these message generators: gencpp;geneus;genlisp;gennodejs;genpy
/opt/ros/melodic/share/genmsg/cmake/pkg-genmsg.cmake.em:56: error: <class 'ModuleNotFoundError'>: No module named 'genmsg'
Traceback (most recent call last):
  File "/usr/lib/python3.8/site-packages/em.py", line 3303, in <module>
    if __name__ == '__main__': main()
  File "/usr/lib/python3.8/site-packages/em.py", line 3301, in main
    invoke(sys.argv[1:])
  File "/usr/lib/python3.8/site-packages/em.py", line 3284, in invoke
    interpreter.wrap(interpreter.file, (file, name))
  File "/usr/lib/python3.8/site-packages/em.py", line 2295, in wrap
    self.fail(e)
  File "/usr/lib/python3.8/site-packages/em.py", line 2284, in wrap
    callable(*args)
  File "/usr/lib/python3.8/site-packages/em.py", line 2359, in file
    self.safe(scanner, done, locals)
  File "/usr/lib/python3.8 ...