STINNER Victor added the comment: I don't think that we need to support compressing/decompressing using the standard input/output.
2013/3/20 Brandon Craig Rhodes <rep...@bugs.python.org>: > > Brandon Craig Rhodes added the comment: > > Larry Hastings <rep...@bugs.python.org> writes: > >> Huh. tar *can* infer it from the data itself. On the other hand, it >> chooses explicitly not to. I guess "tar" knows explicit is better >> than implicit too ;-) > > I am told that the refusal of "tar" to introspect the data is because: > > (a) Tar runs "gunzip -c" (for example) as an external program; it does > not actually compile against libz. > > (b) Streams in UNIX cannot be rewound. Tar cannot look at the first > block of an input pipe and then "put the block back" so that the same > input can be fed directly to "gunzip" as its input. > > (c) Given (a) and (b), tar could only support data introspection of > input from a pipe if it were willing to be a pass-through that, after > reading and introspecting the first block, then fired up "gunzip" and > sent ALL of the blocks through. Which would require multiprocessing, > threading, or async I/O so that tar could both read and write, which > would make tar more complicated. > > (d) Therefore, tar refuses to even look. > > Since Python does bundle compression in its standard library, it can > quite trivially step forward and actually do the data introspection that > tar insists on not doing; the first few bytes of a tar archive are quite > demonstrably different from the first bytes of a gzip stream, if I > recall. > > ---------- > > _______________________________________ > Python tracker <rep...@bugs.python.org> > <http://bugs.python.org/issue13477> > _______________________________________ ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue13477> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
