As I wrote in duplicate issue38496 (with emphasis added):

I'd prefer python3 to require that *all whitespace* at the start of the all the lines is *tabs for the whole file*, or *spaces for the whole file*. And first indented line sets the preference for the whole file.

That way python3 would really disallow mixing spaces and tabs. And the people who like to use tabs for indent (e.g. me) are happy because they can adjust the amount of indent up to their own taste. I'm in the Allman-8 camp for all languages I use.