Gets a list of assignments associated with a site (class). Returns
        a list of TSquareAssignment objects.
        @param site (TSquareSite) - The site to use with the assignment query

        @returns - A list of TSquareSite objects. May be an empty list if
                   the site has defined no assignments.

def get_assignments(self, site):
        """
        Gets a list of assignments associated with a site (class). Returns
        a list of TSquareAssignment objects.
        @param site (TSquareSite) - The site to use with the assignment query

        @returns - A list of TSquareSite objects. May be an empty list if
                   the site has defined no assignments.
        """
        tools = self.get_tools(site)
        assignment_tool_filter = [x.href for x in tools if x.name == 'assignment-grades']
        if not assignment_tool_filter:
            return []
        assignment_tool_url = assignment_tool_filter[0].href
        response = self._session.get(assignment_tool_url)
        response.raise_for_status()
        iframes = self._html_iface.get_iframes(response.text)
        iframe_url = ''
        for frame in iframes:
            if frame['title'] == 'Assignments ':
                iframe_url = frame['src']
        if iframe_url == '':
            print "WARNING: NO ASSIGNMENT IFRAMES FOUND"
        response = self._session.get(iframe_url)
        response.raise_for_status()
        assignment_dict_list = self._html_iface.get_assignments(response.text)
        return [TSquareAssignment(**x) for x in assignment_dict_list]