Martin Panter added the comment: Looking at the current zlib module source code, I confirmed that wbits is passed directly to the deflateInit2(windowBits) and inflateInit2(windowBits) parameters. So the following modes could also be added to the documentation for decompression: * Zero: automatically determine size from zlib header * 32 + logarithm: automatically accept either a zlib or gzip header Also, the compressobj() doc string is out of date. It mentions 8–15 but none of the other options. Paul: Perhaps it would be better to say “wbits” corresponds to the format of the stream, rather than mentioning just the window size as currently proposed. Then hopefully the reader would look to see what value is needed for the raw Deflate format. ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue5784> _______________________________________