On Windows, with 3.7, 3.8.0, and master, none of the demo.py statement here and the examples in #38755 raise an error.  I tried 'python -m module', running from IDLE editor, and interactive IDLE and REPL.  Even the following worked.

>>> s = (b'\xe2\x96\x91'*1111111).decode()
>>> s[-10:]
'░░░░░░░░░░'

susaki, what OS, and do you have the same problem with current Python (at least 3.8)?

Also, susuki, when replying by email, please delete the quoted message.  When your message is added to the web page, the quoted message is redundant and distracting noise.

If this issue effectively duplicates (part of) #14811 and/or #25643, it should be closed as a duplicate of one of them.