user_id ->The user role you want to view
    startup_id -> The startup whose roles you want to view
    role -> The specific role, you'd like to filter ('founder', 'past investor', 'advisor')
    direction ->Either incoming or outgoing

def get_startup_roles(self, user_id=None, startup_id=None, role=None, direction='incoming'):
    """
    user_id ->The user role you want to view
    startup_id -> The startup whose roles you want to view
    role -> The specific role, you'd like to filter ('founder', 'past investor', 'advisor')
    direction ->Either incoming or outgoing
    """

    if user_id is None and startup_id is None:
      raise Exception("You need to provide at least one parameter")
    url = _STARTUP_R.format(c_api=_C_API_BEGINNING,
                                          api=_API_VERSION,
                                          at=self.access_token)
    if user_id is not None:
      url += '&user_id=' + str(user_id)
    if startup_id is not None:
      url += '&startup_id=' + str(startup_id)
    if role is not None:
      url += '&role=' + role
    url += '&direction' + direction
    return _get_request(url)