Comment by warbiscuit

"ascii" the codec does exist under python. It's strictly defined as byte values 0-127, anything in the 128-255 range causes a decoding error...

    >>> b"abc\xf0".decode("ascii")
    UnicodeDecodeError: 'ascii' codec can't decode byte 0xf0 in position 3

Thus, moving the default from "ascii" to an ASCII-superset should have no decoding issues for previously valid files, since those bytes were never valid to start with.