old_contents: #! python3
  # renameDates.py - Renames filenames with American MM-DD-YYYY date format
  # to European DD-MM-YYYY.
  
  import shutil, os, re
  
  # Create a regex that matches files with the American date format.
  datePattern = re.compile(r"""
          ^(.*?)          # all text before the date
          ((0|1)?\d)-     # one or two digits for the month
          ((0|1|2|3)?\d)- # one or two digits for the day
          ((19|20)\d\d)   # four digits for the year
          (.*?)$          # all the text after the date
          """, re.VERBOSE)
  
  # Loop over the files in the working directory.
  for amerFilename in os.listdir('.'):
      mo = datePattern.search(amerFilename)
  
      # Skip files without a date.
      if mo is None:
          continue
  
      # Get the different parts of the filename.
      beforePart = mo.group(1)
      monthPart = mo.group(2)
      dayPart = mo.group(4)
      yearPart = mo.group(6)
      afterPart = mo.group(8)
  
      # Form the European-style filename.
      euroFilename = beforePart + dayPart + '-' + monthPart + '-' + yearPart + afterPart
  
      # Get the full, absolute file paths.
      absWorkingDir = os.path.abspath('.')
      amerFilename = os.path.join(absWorkingDir, amerFilename)
      euroFilename = os.path.join(absWorkingDir, euroFilename)
  
      # Rename the files.
      print('Renaming "%s" to "%s"...' % (amerFilename, euroFilename))  # DEBUG
      #shutil.move(amerFilename, euroFilename)  # uncomment after testing
  
new_contents: #! python3
  """Rename dates
  
  Renames filenames with American MM-DD-YYYY date format to European DD-MM-YYYY date format.
  
  Uses :py:mod:`os` to get the list of files, :py:mod:`re` to find the files with the American
  date format, and :py:mod:`shutil` to rename them.
  
  
  Note:
      * Assumes only files with American date format are in the folder. May also match files with
        European date format.
  
      * Using debug mode: Prints out files to be renamed. Uncomment to rename files.
  
  """
  
  
  def main():
      import shutil, os, re
  
      # Create a regex that matches files with the American date format.
      datePattern = re.compile(r"""
              ^(.*?)          # all text before the date
              ((0|1)?\d)-     # one or two digits for the month
              ((0|1|2|3)?\d)- # one or two digits for the day
              ((19|20)\d\d)   # four digits for the year
              (.*?)$          # all the text after the date
              """, re.VERBOSE)
      """re.compile: Regex object representing American date format MM-DD-YYYY"""
  
      # Loop over the files in the working directory.
      for amerFilename in os.listdir('.'):
          mo = datePattern.search(amerFilename)
  
          # Skip files without a date.
          if mo is None:
              continue
  
          # Get the different parts of the filename.
          beforePart = mo.group(1)
          monthPart = mo.group(2)
          dayPart = mo.group(4)
          yearPart = mo.group(6)
          afterPart = mo.group(8)
  
          # Form the European-style filename.
          euroFilename = beforePart + dayPart + '-' + monthPart + '-' + yearPart + afterPart
  
          # Get the full, absolute file paths.
          absWorkingDir = os.path.abspath('.')
          amerFilename = os.path.join(absWorkingDir, amerFilename)
          euroFilename = os.path.join(absWorkingDir, euroFilename)
  
          # Rename the files.
          print('Renaming "%s" to "%s"...' % (amerFilename, euroFilename))  # DEBUG
          #shutil.move(amerFilename, euroFilename)  # uncomment after testing
  
  
  if __name__ == '__main__':
      main()
  
subject: Update P4_renameDates.py added docstrings and wrapped in main() function