inconsistent use of tabs and spaces in indentation

사용하는 편집기가 notepad++인 경우,

편집 > 공백기능 > 탭을 공백으로 선택 후 저장

 

It means exactly what is sounds like: you indented your code with spaces in some places and with tabs in others. To fix this, in Notepad++, go to Edit -> Blank Operations -> TAB to Space (PEP 8 recommends using spaces vs. tabs).