Fix Python – How do I define a function with optional arguments?

I have a Python function which takes several arguments. Some of these arguments could be omitted in some scenarios.
def some_function (self, a, b, c, d = None, e = None, f = None, g = None, h = None):
#code

The arguments d through h are strings which each have different meanings. It is important that I can choose which optional parameters to ….