code: def get_valid_filename(s):
      
      s = str(s).strip().replace(' ', '_')
      return re.sub(r'(?u)[^-\w.]', '', s)
docs: Shamelessly taken from Django.
      https://github.com/django/django/blob/master/django/utils/text.py
  
      Return the given string converted to a string that can be used for a clean
      filename. Remove leading and trailing spaces; convert other spaces to
      underscores; and remove anything that is not an alphanumeric, dash,
      underscore, or dot.
      >>> get_valid_filename("john's portrait in 2004.jpg")
      'johns_portrait_in_2004.jpg'