Extracted Windows directory detection from NullImporter.__init__. This greatly simplifies the code and fixes issue6727.

Patch from Armin, test from me.

Closes #14158: We now track test_support.TESTFN cleanup, and test_mailbox uses shutil.rmtree for simpler code.

Patch by Ralf Schmitt.

I assume that most users looking at this page are looking for a library
to process XML, not a low-level parser.  First proposed in #11379.

source generates a nifty link to the Mercurial web viewer.

Misc/COPYRIGHT was renamed twelve years ago to LICENSE and later copied
to the main docs, to which there is already a link.

Initial patch by Johannes Vogel. Issue #13491.

Issue #14159: Fix the len() of weak sets to return a better approximation when some objects are dead or dying.
Moreover, the implementation is now O(1) rather than O(n).
Thanks to Yury Selivanov for reporting.

#10713: Improve documentation for \b and \B and add a few tests.  Initial patch and tests by Martin Pool.

Issue #13521: dict.setdefault() now does only one lookup for the given key, making it "atomic" for many purposes.
Patch by Filip Gruszczyński.

- Actually check the contents of the file created by bdist_dumb.
- Don’t use “RECORD” as filename for non-PEP 376 record file
- Don’t start method name with “_test”, it looks like a disabled test
  method instead of an helper method
- Fix some idioms (assertIn, addCleanup)