> Installed the readline module as the arrows do not work when running Python interactively.

This is not a suggested way to fix the issue, especially given that the module you installed is marked as deprecated: https://pypi.org/project/readline/

> Built Python 3.8.1 from source on Fedora 30:

Instead, when you compile, look for a line like this

    Failed to find the necessary bits to build these modules:
    ...
    readline

or

    Failed to build these modules:
    ...
    readline

and then scan through the build log to either find the compiler error or you're most probably missing a dependency like readline-devel