I'd be interested in taking a look at this - would these changes clarify things?

Current (https://docs.python.org/3/library/codecs.html#codecs.StreamWriter):

Writes the concatenated list of strings to the stream (possibly by reusing the write() method). The standard bytes-to-bytes codecs do not support this method.

Proposed:

Writes the concatenated list of strings to the stream by reusing the write() method, and thus does not support infinite or very large generators. The standard bytes-to-bytes codecs do not support this method.