Modules/zlibmodule.c

cpython 3.14 @ ab2d84fe1023/Modules/zlibmodule.c ↗

Modules/zlibmodule.c wraps the zlib C library for zlib. It provides one-shot compress/decompress and stateful Compress/Decompress objects for streaming compression.

Map

Lines	Symbol	Role
1-200	zlib_compress_impl, zlib_decompress_impl	One-shot compression
201-500	Compress object	Stateful deflate stream
501-800	Decompress object	Stateful inflate stream with unconsumed_tail
801-1050	adler32, crc32, module constants	Checksum functions

Reading

wbits encoding

The wbits parameter controls both the window size and the format:

• wbits=15 (default): zlib format (header + adler32 checksum)
• wbits=31 (15 + 16): gzip format (gzip header + CRC32)
• wbits=-15: raw deflate (no header, no checksum)

Compress.compress

Compress.compress(data) calls deflate(Z_NO_FLUSH) on the input and returns whatever output is available. Compress.flush(mode) calls deflate(Z_SYNC_FLUSH) or deflate(Z_FINISH). Callers must call flush() to drain the stream.

// CPython: Modules/zlibmodule.c:340 zlib_Compress_compress_impl
static PyObject *
zlib_Compress_compress_impl(compobject *self, Py_buffer *data)
{
    ...
    Py_BEGIN_ALLOW_THREADS
    err = deflate(&self->zst, Z_NO_FLUSH);
    Py_END_ALLOW_THREADS
    ...
}

Decompress.unconsumed_tail

If Decompress.decompress(data, max_length=0) hits max_length before exhausting the input, it stores the unused input in self.unconsumed_tail. Callers must call decompress again with unconsumed_tail to drain remaining data.

gopy notes

Not yet ported. zlib is used by zipfile, gzip, and http.client. The Go backend will use compress/zlib and compress/flate. Planned path: module/zlib/.