SyntaxWarning: invalid escape sequence '\.'

Installing software-properties gives

--->
/usr/lib/python3/dist-packages/softwareproperties/gtk/DialogMirror.py:197: SyntaxWarning: invalid escape sequence '\.'
  elif re.match("^((ftp)|(http)|(file)|(rsync)|(https))://([a-z]|[A-Z]|[0-9]|:|/|\.|~)+$", uri) == None:
<---

Marked as "wishlist" importance because Python still passes that to re.match as '\.' instead of '.', so the behavior is correct, as can be confirmed with

--->
% python3 -c 'print("\.")'
<string>:1: SyntaxWarning: invalid escape sequence '\.'
\.
<---

In a future Python version they will be eventually a SyntaxError[1].

[1] https://docs.python.org/3/reference/lexical_analysis.html#escape-sequences