Release notes for Python 3.6.6

Python 3.6.6 final

Release date: 2018-06-27

There were no new changes in version 3.6.6.

Python 3.6.6 release candidate 1

Release date: 2018-06-11

Core and Builtins

  • bpo-33786: Fix asynchronous generators to handle GeneratorExit in athrow() correctly
  • bpo-30654: Fixed reset of the SIGINT handler to SIG_DFL on interpreter shutdown even when there was a custom handler set previously. Patch by Philipp Kerling.
  • bpo-33622: Fixed a leak when the garbage collector fails to add an object with the __del__ method or referenced by it into the gc.garbage list. PyGC_Collect() can now be called when an exception is set and preserves it.
  • bpo-31849: Fix signed/unsigned comparison warning in pyhash.c.
  • bpo-33391: Fix a leak in set_symmetric_difference().
  • bpo-28055: Fix unaligned accesses in siphash24(). Patch by Rolf Eike Beer.
  • bpo-33231: Fix potential memory leak in normalizestring().
  • bpo-29922: Improved error messages in ‘async with’ when __aenter__() or __aexit__() return non-awaitable object.
  • bpo-33199: Fix ma_version_tag in dict implementation is uninitialized when copying from key-sharing dict.
  • bpo-33041: Fixed jumping when the function contains an async for loop.
  • bpo-32282: Fix an unnecessary ifdef in the include of VersionHelpers.h in socketmodule on Windows.
  • bpo-21983: Fix a crash in ctypes.cast() in case the type argument is a ctypes structured data type. Patch by Eryk Sun and Oren Milman.


  • bpo-30167: Prevent site.main() exception if PYTHONSTARTUP is set. Patch by Steve Weber.
  • bpo-33812: Datetime instance d with non-None tzinfo, but with d.tzinfo.utcoffset(d) returning None is now treated as naive by the astimezone() method.
  • bpo-30805: Avoid race condition with debug logging
  • bpo-33767: The concatenation (+) and repetition (*) sequence operations now raise TypeError instead of SystemError when performed on mmap.mmap objects. Patch by Zackery Spytz.
  • bpo-32684: Fix gather to propagate cancellation of itself even with return_exceptions.
  • bpo-33674: Fix a race condition in SSLProtocol.connection_made() of asyncio.sslproto: start immediately the handshake instead of using call_soon(). Previously, data_received() could be called before the handshake started, causing the handshake to hang or fail.
  • bpo-31647: Fixed bug where calling write_eof() on a _SelectorSocketTransport after it’s already closed raises AttributeError.
  • bpo-33672: Fix Task.__repr__ crash with Cython’s bogus coroutines
  • bpo-33469: Fix RuntimeError after closing loop that used run_in_executor
  • bpo-11874: Use a better regex when breaking usage into wrappable parts. Avoids bogus assertion errors from custom metavar strings.
  • bpo-30877: Fixed a bug in the Python implementation of the JSON decoder that prevented the cache of parsed strings from clearing after finishing the decoding. Based on patch by c-fos.
  • bpo-33548: tempfile._candidate_tempdir_list should consider common TEMP locations
  • bpo-33542: Prevent uuid.get_node from using a DUID instead of a MAC on Windows. Patch by Zvi Effron
  • bpo-26819: Fix race condition with ReadTransport.resume_reading in Windows proactor event loop.
  • bpo-28556: Minor fixes in typing module: add annotations to NamedTuple.__new__, pass *args and **kwds in Generic.__new__. Original PRs by Paulius Šarka and Chad Dombrova.
  • bpo-20087: Updated alias mapping with glibc 2.27 supported locales.
  • bpo-33422: Fix trailing quotation marks getting deleted when looking up byte/string literals on pydoc. Patch by Andrés Delfino.
  • bpo-33197: Update error message when constructing invalid inspect.Parameters Patch by Dong-hee Na.
  • bpo-33383: Fixed crash in the get() method of the dbm.ndbm database object when it is called with a single argument.
  • bpo-33329: Fix multiprocessing regression on newer glibcs
  • bpo-991266: Fix quoting of the Comment attribute of http.cookies.SimpleCookie.
  • bpo-33131: Upgrade bundled version of pip to 10.0.1.
  • bpo-33308: Fixed a crash in the parser module when converting an ST object to a tree of tuples or lists with line_info=False and col_info=True.
  • bpo-33263: Fix FD leak in _SelectorSocketTransport Patch by Vlad Starostin.
  • bpo-33256: Fix display of <module> call in the html produced by cgitb.html(). Patch by Stéphane Blondon.
  • bpo-33203: random.Random.choice() now raises IndexError for empty sequences consistently even when called from subclasses without a getrandbits() implementation.
  • bpo-33224: Update difflib.mdiff() for PEP 479. Convert an uncaught StopIteration in a generator into a return-statement.
  • bpo-33209: End framing at the end of C implementation of pickle.Pickler.dump().
  • bpo-32861: The urllib.robotparser’s __str__ representation now includes wildcard entries and the “Crawl-delay” and “Request-rate” fields. Patch by Michael Lazar.
  • bpo-33096: Allow ttk.Treeview.insert to insert iid that has a false boolean value. Note iid=0 and iid=False would be same. Patch by Garvit Khatri.
  • bpo-33127: The ssl module now compiles with LibreSSL 2.7.1.
  • bpo-33021: Release the GIL during fstat() calls, avoiding hang of all threads when calling mmap.mmap(), os.urandom(), and random.seed(). Patch by Nir Soffer.
  • bpo-27683: Fix a regression in ipaddress that result of hosts() is empty when the network is constructed by a tuple containing an integer mask and only 1 bit left for addresses.
  • bpo-32844: Fix wrong redirection of a low descriptor (0 or 1) to stderr in subprocess if another low descriptor is closed.
  • bpo-31908: Fix output of cover files for trace module command-line tool. Previously emitted cover files only when --missing option was used. Patch by Michael Selik.
  • bpo-31457: If nested log adapters are used, the inner process() methods are no longer omitted.
  • bpo-16865: Support arrays >=2GiB in ctypes. Patch by Segev Finer.
  • bpo-31238: pydoc: the stop() method of the private ServerThread class now waits until DocServer.serve_until_quit() completes and then explicitly sets its docserver attribute to None to break a reference cycle.


  • bpo-33503: Fix broken pypi link
  • bpo-33421: Add missing documentation for typing.AsyncContextManager.
  • bpo-33378: Add Korean language switcher for
  • bpo-33276: Clarify that the __path__ attribute on modules cannot be just any value.
  • bpo-33201: Modernize documentation for writing C extension types.
  • bpo-33195: Deprecate Py_UNICODE usage in c-api/arg document. Py_UNICODE related APIs are deprecated since Python 3.3, but it is missed in the document.
  • bpo-33126: Document PyBuffer_ToContiguous().
  • bpo-27212: Modify documentation for the islice() recipe to consume initial values up to the start index.
  • bpo-28247: Update zipapp documentation to describe how to make standalone applications.
  • bpo-18802: Documentation changes for ipaddress. Patch by Jon Foster and Berker Peksag.
  • bpo-27428: Update documentation to clarify that WindowsRegistryFinder implements MetaPathFinder. (Patch by Himanshu Lakhara)
  • bpo-8243: Add a note about curses.addch and curses.addstr exception behavior when writing outside a window, or pad.
  • bpo-31432: Clarify meaning of CERT_NONE, CERT_OPTIONAL, and CERT_REQUIRED flags for ssl.SSLContext.verify_mode.


  • bpo-33655: Ignore test_posix_fallocate failures on BSD platforms that might be due to running on ZFS.
  • bpo-19417: Add


  • bpo-5755: Move -Wstrict-prototypes option to CFLAGS_NODIST from OPT. This option emitted annoying warnings when building extension modules written in C++.
  • bpo-33614: Ensures module definition files for the stable ABI on Windows are correctly regenerated.
  • bpo-33522: Enable CI builds on Visual Studio Team Services at
  • bpo-33012: Add -Wno-cast-function-type for gcc 8 for silencing warnings about function casts like casting to PyCFunction in method definition lists.
  • bpo-33394: Enable the verbose build for extension modules, when GNU make is passed macros on the command line.


  • bpo-33184: Update Windows installer to OpenSSL 1.0.2o.


  • bpo-33184: Update macOS installer build to use OpenSSL 1.0.2o.


  • bpo-33656: On Windows, add API call saying that tk scales for DPI. On Windows 8.1+ or 10, with DPI compatibility properties of the Python binary unchanged, and a monitor resolution greater than 96 DPI, this should make text and lines sharper. It should otherwise have no effect.
  • bpo-33768: Clicking on a context line moves that line to the top of the editor window.
  • bpo-33763: IDLE: Use read-only text widget for code context instead of label widget.
  • bpo-33664: Scroll IDLE editor text by lines. Previously, the mouse wheel and scrollbar slider moved text by a fixed number of pixels, resulting in partial lines at the top of the editor box. The change also applies to the shell and grep output windows, but not to read-only text views.
  • bpo-33679: Enable theme-specific color configuration for Code Context. Use the Highlights tab to see the setting for built-in themes or add settings to custom themes.
  • bpo-33642: Display up to maxlines non-blank lines for Code Context. If there is no current context, show a single blank line.
  • bpo-33628: IDLE: Cleanup and its test.
  • bpo-33564: IDLE’s code context now recognizes async as a block opener.
  • bpo-29706: IDLE now colors async and await as keywords in 3.6. They become full keywords in 3.7.
  • bpo-21474: Update word/identifier definition from ascii to unicode. In text and entry boxes, this affects selection by double-click, movement left/right by control-left/right, and deletion left/right by control-BACKSPACE/DEL.
  • bpo-33204: IDLE: consistently color invalid string prefixes. A ‘u’ string prefix cannot be paired with either ‘r’ or ‘f’. Consistently color as much of the prefix, starting at the right, as is valid. Revise and extend colorizer test.
  • bpo-32831: Add docstrings and tests for codecontext.


  • bpo-33189: now recognizes only literal strings as docstrings and translatable strings, and rejects bytes literals and f-string expressions.
  • bpo-31920: Fixed handling directories as arguments in the pygettext script. Based on patch by Oleg Krasnikov.
  • bpo-29673: Fix pystackv and pystack gdbinit macros.
  • bpo-32885: Add an -n flag for Tools/scripts/ to disbale automatic backup creation (files with ~ suffix).
  • bpo-31583: Fix 2to3 for using with –add-suffix option but without –output-dir option for relative path to files in current directory.


  • bpo-32374: Document that m_traverse for multi-phase initialized modules can be called with m_state=NULL, and add a sanity check