Note that the URL can also be a file: URL, which the quote fetcher takes to be the path to an executable script. It will pass any command-line arguments to it that you have specified, and feed the stdout to the page parser. For example, you might have a script called getquote.sh that contains custom quote logic, taking the symbol as a single parameter. Your URL would be “file:/path/to/getquote.sh %1”.

Windows issues -
I normally run kmymoney and this script in linux. Before posting this here, I installed kmymoney 4.8.2, and python 3.7 in a Windows 10 VM in virtualbox, to test this in windows. I can run kmquotes.py from a windows terminal (cmd.exe) and retrieve quotes, so kmquotes can run in windows.

However, I haven't figured out how to create a kmymoney online quote source in windows that runs a script. Regardless of how I set the URL to kmquotes, it fails in kmymoney when I try to retrieve online quotes with:
Unable to launch: kmquotes.py XXXX
Unable to update price for XXXX (empty quote data)

is called as "/bin/sh" "-c" "/home/user/bin/price.sh %1" where %1 will
be replaced with the actual investment symbol.