使用pandas时SettingWithCopyWarning

1. C:\Users\xxx\AppData\Local\Programs\Python\Python37\python.exe D:/book/Python/workspace/autooss/lib/readExcelHelper.py
   
2. C:\Users\xxx\AppData\Local\Programs\Python\Python37\lib\site-packages\pandas\core\indexing.py:362: SettingWithCopyWarning:
   
3. A value is trying to be set on a copy of a slice from a DataFrame.
   
4. Try using .loc[row_indexer,col_indexer] = value instead
   
5. 
   
6. See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
   
7.   self.obj[key] = _infer_fill_value(value)
   
8. C:\Users\xxx\AppData\Local\Programs\Python\Python37\lib\site-packages\pandas\core\indexing.py:543: SettingWithCopyWarning:
   
9. A value is trying to be set on a copy of a slice from a DataFrame.
   
10. Try using .loc[row_indexer,col_indexer] = value instead
    
11. 
    
12. See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
    
13.   self.obj[item] = s
    
14. D:/book/Python/workspace/autooss/lib/readExcelHelper.py:77: SettingWithCopyWarning:
    
15. A value is trying to be set on a copy of a slice from a DataFrame
    
16. 
    
17. See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
    
18.   df2.drop_duplicates(['Location', 'Interface_prefix'], keep='first', inplace=True)
    
19. C:\Users\xxx\AppData\Local\Programs\Python\Python37\lib\site-packages\pandas\core\frame.py:3940: SettingWithCopyWarning:
    
20. A value is trying to be set on a copy of a slice from a DataFrame
    
21. 
    
22. See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
    
23.   errors=errors)
    
24. 
    
25. Process finished with exit code 0
    

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为什么 df2.drop_duplicates(['Location', 'Interface_prefix'], keep='first', inplace=True) 会出现这个warning呢，求指教，谢谢