# Pastebin hmOBWTpT
$ cat x.py 
for b in range(1, 128):
    if b in b"""\n\r"'01234567NU\\abfnrtuvx""":
        continue
    assert eval(r"'\%c'" % b) == '\\' + chr(b)
$ pypy3 -Wall  x.py  # no warning, this is the bug
$ python3 -Wall  x.py  # lots of warnings
<string>:1: DeprecationWarning: invalid escape sequence \

<string>:1: DeprecationWarning: invalid escape sequence \
<string>:1: DeprecationWarning: invalid escape sequence \
<string>:1: DeprecationWarning: invalid escape sequence \
<string>:1: DeprecationWarning: invalid escape sequence \
<string>:1: DeprecationWarning: invalid escape sequence \
<string>:1: DeprecationWarning: invalid escape sequence \
<string>:1: DeprecationWarning: invalid escape sequence \
<string>:1: DeprecationWarning: invalid escape sequence \	
<string>:1: DeprecationWarning: invalid escape sequence \
.....