I forgot: this is what Nick's example now looks like:

$ ./python -Wall escape_warning.py
Traceback (most recent call last):
  File "escape_warning.py", line 1, in <module>
    import bad_escape
  File "/home/eric/local/python/cpython/bad_escape.py", line 1
    print('\d')
         ^
SyntaxError: invalid escape sequence \d