You cannot combine HTTP GET query parameters (ones in URL) and HTTP POST parameters.
This is limitation on the HTTP protocol level, not in Python or Zoho.
Most likely you are doing it wrong. Revisit Zoho documentation how it should be done.
Here is another old library doing Zoho + CRM, written in Python. You might want to check it for inspiration: https://github.com/miohtama/mfabrik.zoho