code: def use_double_hash(password_hash=None):
      
      # Default to plaintext for backward compatibility with
      # SECURITY_PASSWORD_SINGLE_HASH = False
      single_hash = config_value('PASSWORD_SINGLE_HASH') or {'plaintext'}
  
      if password_hash is None:
          scheme = _security.password_hash
      else:
          scheme = _pwd_context.identify(password_hash)
  
      return not (single_hash is True or scheme in single_hash)
docs: Return a bool indicating whether a password should be hashed twice.