If the file is just a class I usually put example usage with some default arguments in that block by itself. There is no reason for a "main" function. It's a nice obvious block that doesn't run when someone imports the class but if they're looking at the class there is a really obvious place to see the class usage. No confusion about what "main()" is meant to do.

if __name__ == '__main__':
    # MyClass example Usage
    my_object = MyClass()
    my_object.my_method()