>>> from selenium import webdriver
>>> driver = webdriver.Firefox()

>>> driver.get("http://www.baidu.com")

>>> driver.find_element_by_id("kw").send_keys("selenium2")

到第四句出现下面错误，怎么解决？？？？？

Traceback (most recent call last):
  File "<pyshell#8>", line 1, in <module>
    driver.find_element_by_id("kw").send_keys("selenium2")
  File "F:\python\lib\site-packages\selenium\webdriver\remote\webelement.py", line 352, in send_keys
    'value': keys_to_typing(value)})
  File "F:\python\lib\site-packages\selenium\webdriver\remote\webelement.py", line 501, in _execute
    return self._parent.execute(command, params)
  File "F:\python\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 311, in execute
    self.error_handler.check_response(response)
  File "F:\python\lib\site-packages\selenium\webdriver\remote\errorhandler.py", line 237, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.ElementNotInteractableException: Message: Element is not visible