zip.SetFileCompression(id, idx, method[, flags])
idx in the zip archive
specified by id to the compression method specified in method. The optional flags argument
can be used to define the compression level, 1 being fastest compression and 9 highest. Allowed
values are 1-9 or 0 to use the compressor's default setting.
The method parameter must be one of the following constants:
#ZIP_CM_DEFAULT:#ZIP_CM_DEFLATE.
#ZIP_CM_STORE:
#ZIP_CM_BZIP2:
#ZIP_CM_DEFLATE:
Note that only #ZIP_CM_DEFLATE and #ZIP_CM_STORE can be assumed to be universally supported.
Also note that the change to the zip archive isn't done immediately but is postponed until you call zip.CloseArchive().