Invalid escape sequence 'x' (W605)

As of Python 3.6, a backslash-character pair that is not a valid escape sequence now generates a DeprecationWarning. This will eventually become a SyntaxError.

Anti-pattern

regex = '\.png$'

Best practice

regex = r'\.png$'

Additional links

• https://docs.python.org/3/reference/lexical_analysis.html#string-and-bytes-literals
• https://docs.python.org/3/whatsnew/3.6.html#deprecated-python-behavior