"inconsistent use of tabs and spaces in indentation"
Don't use tabs.
- Set your editor to use 4 spaces for indentation.
- Make a search and replace to replace all tabs with 4 spaces.
- Make sure your editor is set to display tabs as 8 spaces.
Note: The reason for 8 spaces for tabs is so that you immediately notice when tabs have been inserted unintentionally - such as when copying and pasting from example code that uses tabs instead of spaces.