python selenium模块使用出错，这个怎么改？

测试积点老人

错误代码如下：

1. File "/usr/local/lib/python2.7/dist-packages/selenium-3.0.0b2-py2.7.egg/selenium/webdriver/firefox/webdriver.py", line 65, in __init__
   
2. self.service.start()
   
3. File "/usr/local/lib/python2.7/dist-packages/selenium-3.0.0b2-py2.7.egg/selenium/webdriver/common/service.py", line 71, in start
   
4. os.path.basename(self.path), self.start_error_message)
   
5. selenium.common.exceptions.WebDriverException: Message: 'geckodriver' executable needs to be in PATH.
   
6. 
   
7. Exception AttributeError: "'Service' object has no attribute 'process'" in <bound method Service.__del__ of <selenium.webdriver.firefox.service.Service object at 0x7f753ad53390>> ignored

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是不是没有安装什么啊？