The codec design allows extending the constructors using keyword arguments, however I'd rather not add a generic **kws argument to the base classes since this would hide errors (unknown or unsupported keywords, mispellings, etc.).
Isn't such an argument required at least for StreamReaderWriter, because it actually instantiates two objects?
class StreamReaderWriter: def __init__(self, stream, Reader, Writer, errors='strict'):
""" ... Reader, Writer must be factory functions or classes providing the StreamReader, StreamWriter interface resp. """ self.stream = stream self.reader = Reader(stream, errors) self.writer = Writer(stream, errors)
Hmm... you'd better not need to have two different set of keyword arguments for Reader and Writer. Is that limitation acceptable? If it is, then the list of changes becomes 1) add **kw to codecs.open, and 2) add **kw to StreamReaderWriter's constructor, and apply it to the Reader() and Writer() calls.
The encoder and decoder functions must work stateless.
OK, then they're not suitable for encryption (in general, though they'd work fine for ECB mode).