old_contents: from win_unc.sanitizors import sanitize_username, sanitize_unc_path
  
  
  def is_valid_drive_letter(string):
      """
      Drive letters are one character in length and between "A" and "Z". Case does not matter.
      """
      return (len(string) == 1
              and string[0].isalpha())
  
  
  def is_valid_unc_path(string):
      """
      Valid UNC paths are at least three characters long, begin with "\\", do not start or end with
      whitepsace, and do not contain certain invalid characters (see `sanitize_unc_path`).
      """
      return (len(string) > 2
              and string.startswith('\\\\')
              and string == string.strip()
              and string == sanitize_unc_path(string))
  
  
  def is_valid_username(string):
      """
      A valid Windows username (logon) is a non-empty string that does not start or end with
      whitespace, and does not contain certain invalid characters (see `sanitize_username`).
      """
      return (len(string) > 0
              and string == string.strip()
              and string == sanitize_username(string))
  
new_contents: from win_unc.internal.utils import take_while
  from win_unc.sanitizors import sanitize_username, sanitize_unc_path
  
  
  def is_valid_drive_letter(string):
      """
      Drive letters are one character in length and between "A" and "Z". Case does not matter.
      """
      return (len(string) == 1
              and string[0].isalpha())
  
  
  def is_valid_unc_path(string):
      """
      Valid UNC paths are at least three characters long, begin with exactly two backslashes, not
      start or end with whitepsace, and do not contain certain invalid characters
      (see `sanitize_unc_path`).
      """
      return (len(string) > 2
              and len(take_while(lambda c: c == '\\', string)) == 2
              and string == string.strip()
              and string == sanitize_unc_path(string))
  
  
  def is_valid_username(string):
      """
      A valid Windows username (logon) is a non-empty string that does not start or end with
      whitespace, and does not contain certain invalid characters (see `sanitize_username`).
      """
      return (len(string) > 0
              and string == string.strip()
              and string == sanitize_username(string))
  
subject: Fix bad refactor of is_valid_unc_path