Python 3 is stricter with regard to using tabs instead of space (PEP8):
	Spaces are the preferred indentation method.

	Tabs should be used solely to remain consistent with code that
	is already indented with tabs.

	Python 3 disallows mixing the use of tabs and spaces for
	indentation.

	Python 2 code indented with a mixture of tabs and spaces should
	be converted to using spaces exclusively.