old_contents: '''utilities for managing directories
  
  Copyright 2017 Roy E. Lowrance
  
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
  
   http://www.apache.org/licenses/LICENSE-2.0
  
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on as "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing premission and
  limitation under the license.
  '''
  
  import os
  import pdb
  import string
  import unittest
  
  
  def assure_exists(dir_path):
      if not os.path.exists(dir_path):
          os.makedirs(dir_path)  # make all intermediate directories
      return dir_path
  
  
  def _make_invalid_characters():
      'return translation table suitable for s.translate()'
      bad_linux = '/\x00'
      # bad_macos = ':/'
      bad_ntfs = '"*:<>?\|'   # plus 0x00 - 0x1F plus 0x7F
      bad_os = bad_ntfs + bad_linux  # bad_macos is in these two
      low_codes = '\x01\x02\x03\x04\x05\x06\x07\x08\x09\x10\x11\x12\x13\x14\x15'
      assert len(low_codes) == 15, low_codes
      high_code = '\x7f'
      return bad_os + low_codes + high_code
  
  
  _invalid_characters = _make_invalid_characters()
  
  
  def always_valid_filename(s, replacement_char='-'):
      '''return a new string that is acceeptable to Linux, MacOS, and Linux
      ref: https://en.wikipedia.org/wiki/Filename
      '''
      table = string.maketrans(_invalid_characters, replacement_char * len(_invalid_characters))
      return s.translate(table)
  
  
  class Test_always_valid_filename(unittest.TestCase):
      def test1(self):
          s = 'abc\x03/:"*<>?\\|'
          result = always_valid_filename(s)
          self.assertEqual('abc----------', result)
  
  
  if __name__ == '__main__':
      if False:
          pdb
      unittest.main()
  
new_contents: '''utilities for managing directories
  
  Copyright 2017 Roy E. Lowrance
  
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
  
   http://www.apache.org/licenses/LICENSE-2.0
  
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on as "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing premission and
  limitation under the license.
  '''
  
  import os
  import pdb
  import string
  import unittest
  
  
  def assure_exists(dir_path):
      if not os.path.exists(dir_path):
          os.makedirs(dir_path)  # make all intermediate directories
      return dir_path
  
  
  def _make_invalid_characters():
      'return translation table suitable for s.translate()'
      bad_linux = '/\x00'
      # bad_macos = ':/'
      bad_ntfs = '"*:<>?\|'   # plus 0x00 - 0x1F plus 0x7F
      bad_os = bad_ntfs + bad_linux  # bad_macos is in these two
      low_codes = '\x01\x02\x03\x04\x05\x06\x07\x08\x09\x10\x11\x12\x13\x14\x15'
      assert len(low_codes) == 15, low_codes
      high_code = '\x7f'
      return bad_os + low_codes + high_code
  
  
  _invalid_characters = _make_invalid_characters()
  
  
  def always_valid_filename(s, replacement_char='-'):
      '''return a new string that is acceeptable to Linux, MacOS, and Linux
      ref: https://en.wikipedia.org/wiki/Filename
      '''
      # ref: https://docs.python.org/3.6/library/stdtypes.html?highlight=maketrans#str.maketrans
      table = str.maketrans(_invalid_characters, replacement_char * len(_invalid_characters))
      return s.translate(table)
  
  
  class Test_always_valid_filename(unittest.TestCase):
      def test1(self):
          s = 'abc\x03/:"*<>?\\|'
          result = always_valid_filename(s)
          self.assertEqual('abc----------', result)
  
  
  if __name__ == '__main__':
      if False:
          pdb
      unittest.main()
  
subject: use python3 new API for str.maketrans