> On Windows, with 3.7, 3.8.0, and master, neither the posted comment, the one in the file, not the initial statement in #34979 give the SyntaxError.

Just tried again on my corporate laptop with the downloaded file from this site:

Microsoft Windows [Version 10.0.16299.1451]
(c) 2017 Microsoft Corporation. All rights reserved.

D:\Downloads>py
Python 3.8.0 (tags/v3.8.0:fa919fd, Oct 14 2019, 19:37:50) [MSC v.1916 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> quit()

D:\Downloads>py tst112.py
  File "tst112.py", line 1
SyntaxError: Non-UTF-8 code starting with '\xe2' in file tst112.py on line 1, but no encoding declared; see http://python.org/dev/peps/pep-0263/ for details

d:\Downloads>py -3.7
Python 3.7.4 (tags/v3.7.4:e09359112e, Jul  8 2019, 20:34:20) [MSC v.1916 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> quit()

d:\Downloads>py -3.7 tst112.py
  File "tst112.py", line 1
SyntaxError: Non-UTF-8 code starting with '\xe2' in file tst112.py on line 1, but no encoding declared; see http://python.org/dev/peps/pep-0263/ for details