How to make communication between computer and Quartus using Python?

From how I read your question you want to generate signals, and you think you can send something like generate_sinewave to quartus, which will than use an fpga to generate this. If you think this, you'll need to change your ideas. You first need to write code which describes what the FPGA should do. This is than compiled by quartus and can be loaded into the FPGA. In your case you'll need to write code that listens to input from a computer and, based on that command, generate some output signal. I suggest using a uart for the input, since it is a relatively easy protocol and there are plenty of examples and open-source cores for that.