def _convert(self, value):
"""Returns a Encryption object from the given string.
PasswordHash instances or None values will return unchanged.
Strings will be hashed and the resulting PasswordHash returned.
Any other input will result in a TypeError.
"""
if isinstance(value, Encryption):
return value
elif isinstance(value, basestring):
return Encryption.new(value, self.cipher_key)
elif value is not None:
raise TypeError(
'Cannot convert {} to a EncryptedValue'.format(type(value)))
