Your problems are related to the fact that you are using Windows. While there are multiple libraries and tools to perform the conversion with Linux (including Python wrappers), these may be not available for Windows or difficult to setup.
The simplest solution would be calling a command line tool from within Python (os.system or subprocess.call). One candidate providing ready to use Windows executables would be ImageMagick: Install from Binary Distribution
]. You can also use the Windows version of Inkscape
] which provides command line options for conversions without starting the GUI.