To speak with SQL Server you need to use the TDS protocol. To use that protocol you need to use a driver of some sort. I believe the most common solution in the world of Python is to use an ODBC driver for SQL Server and then a Python module on top of that.
But you could also have a driver written in Python that speaks TDS directly to SQL Server. A quick googling led me to https://github.com/denisenkom/pytds, which seems to promise exactly this. I will need to add disclaimer that I don't know how good or bad pytds is, but you can give it a try.