Read setup.py to string
        :return:

def setup_py_source(self):  # type: () -> Optional[str]
        """
        Read setup.py to string
        :return:
        """
        if not self.setup_source:
            self.setup_source = self._read_file("setup.py")
        if not self.setup_source:
            self.setup_source = self._read_file("setup")  # rare case
        return self.setup_source