To return a value, simply use the return
JavaScript keyword in the string passed to the execute_script()
method, e.g.
>>> from selenium import webdriver
>>> wd = webdriver.Firefox()
>>> wd.get("http://localhost/foo/bar")
>>> wd.execute_script("return 5")
5
>>> wd.execute_script("return true")
True
>>> wd.execute_script("return {foo: 'bar'}")
{u'foo': u'bar'}
>>> wd.execute_script("return foobar()")
u'eli'