Issue 21717: Exclusive mode for ZipFile and TarFile

I noticed that while lzma and bz2 already support the "x" (create a new file, raise if it already exists) flag, zipfile and tarfile don't know about it yet.  It would be an useful addition, just as it is useful for regular open.

A quick look at both modules show that this likely only requires a little bit more than updating the checks in the corresponding constructors to allow "x" mode, as the modes are passed (nearly) transparently to the open() builtin.

Here's a patch for tarfile.

Ping.

Here's an updated patch. Thanks Serhiy.

Added more comments.

Here is a patch for zipfile.

Updated patch. Thanks again, Serhiy.

New changeset ed9e9e6b3c1e by Berker Peksag in branch 'default':
Issue #21717: tarfile.open() now supports 'x' (exclusive creation) mode.
https://hg.python.org/cpython/rev/ed9e9e6b3c1e

Thanks for the review, Serhiy. I'll take a look at the zipfile patch tomorrow.

Could you look on zipfile patch Berker? It is simpler than tarfile patch.

LGTM. I left two minor comments on Rietveld. Sorry for the delay.

New changeset b2a8c30d8ddb by Serhiy Storchaka in branch 'default':
Issue #21717: The zipfile.ZipFile.open function now supports 'x' (exclusive
https://hg.python.org/cpython/rev/b2a8c30d8ddb

messages: + msg235679

messages: + msg235488

messages: + msg235478

type: enhancement
versions: - Python 3.4
keywords: + patch
nosy: + berker.peksag, serhiy.storchaka, lars.gustaebel

messages: + msg221358
stage: patch review