Deprecation warning over invalid escape sequences in Python 3.8

[tirkarthi]

These doesn't seem to be part of the library but more related to utility scripts. Using raw strings or escaping them will fix this,

find . -iname '*.py'  | xargs -P 4 -I{} python3.8 -Wall -m py_compile {}

./docs/conf.py:241: DeprecationWarning: invalid escape sequence \D
  'preamble': '\DeclareUnicodeCharacter{00A0}{}',
./tools/mkdoc.py:109: DeprecationWarning: invalid escape sequence \w
  cpp_group = '([\w:]+)'
./tools/mkdoc.py:110: DeprecationWarning: invalid escape sequence \[
  param_group = '([\[\w:\]]+)'

[YannickJadoul]

Thanks for reporting, @tirkarthi!

#2281 should close this :-)