_INDEX_REGEX = {"name": {"$regex": "^(?!.*\$)"}}
_SYSTEM_FILTER = {"filter": {"name": {"$regex": "^(?!system\.)"}}}

python3.6 -We
Python 3.6.5 (default, Mar 30 2018, 06:42:10)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.39.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> '\s'
  File "<stdin>", line 1
SyntaxError: invalid escape sequence \s
>>> '\$'
  File "<stdin>", line 1
SyntaxError: invalid escape sequence \$
>>> '\.'
  File "<stdin>", line 1
SyntaxError: invalid escape sequence \.