"PYTHON": "3.7.3",
"RRDTOOL": "1.7.1",
"PYTHON_RRDTOOL": "0.1.16",

This is just a small thing, but it took me some time to understand why my program was not working properly.

Normally I always leave a space between option and argument. But for the options -a and -n the space must be omitted exceptionally, otherwise RRDTool will return an error.
Example:
'-a SVG', # unsupported graphics format ' SVG'
'-n DEFAULT:10', # invalid text property format
'-n TITLE:14:Times', #invalid text property format

Invoking RRDTool from bash with spaces works properly.