new_contents: #! /usr/bin/env python
  """
  Look for escape sequences deprecated in Python 3.6.
  
  Python 3.6 deprecates a number of non-escape sequences starting with `\` that
  were accepted before. For instance, '\(' was previously accepted but must now
  be written as '\\(' or r'\('.
  
  """
  from __future__ import division, absolute_import, print_function
  
  import sys
  
  def main(root):
      """Find deprecated escape sequences.
  
      Checks for deprecated escape sequences in ``*.py files``. If `root` is a
      file, that file is checked, if `root` is a directory all ``*.py`` files
      found in a recursive descent are checked.
  
      If a deprecated escape sequence is found, the file and line where found is
      printed. Note that for multiline strings the line where the string ends is
      printed and the error(s) are somewhere in the body of the string.
  
      Parameters
      ----------
      root : str
          File or directory to check.
      Returns
      -------
      None
  
      """
      count = 0
  
      if sys.version_info[:2] >= (3, 6):
          import ast
          import tokenize
          import warnings
          from pathlib import Path
  
          base = Path(root)
          paths = base.rglob("*.py") if base.is_dir() else [base]
          for path in paths:
              # use tokenize to auto-detect encoding on systems where no
              # default encoding is defined (e.g. LANG='C')
              with tokenize.open(str(path)) as f:
                  with warnings.catch_warnings(record=True) as w:
                      warnings.simplefilter('always')
                      tree = ast.parse(f.read())
                  if w:
                      print("file: ", str(path))
                      for e in w:
                          print('line: ', e.lineno, ': ', e.message)
                      print()
                      count += len(w)
      else:
          raise RuntimeError("Python version must be >= 3.6")
  
      print("Errors Found", count)
  
  
  if __name__ == "__main__":
      from argparse import ArgumentParser
  
      parser = ArgumentParser(description="Find deprecated escaped characters")
      parser.add_argument('root', help='directory or file to be checked')
      args = parser.parse_args()
      main(args.root)
  
subject: Add tool to check for deprecated escaped characters.