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PEP 487: Simpler customization of class creation
by Martin Teichmann 04 Jul '16

04 Jul '16

Hi list, just recently, I posted about the implementation of PEP 487. The discussion quickly diverted to PEP 520, which happened to be strongly related. Hoping to get some comments about the rest of PEP 487, I took out the part that is also in PEP 520. I attached the new version of the PEP. The implementation can be found on the Python issue tracker: http://bugs.python.org/issue27366 So PEP 487 is about simplifying the customization of class creation. Currently, this is done via metaclasses, which are very powerful, but often inflexible, as it is hard to combine two metaclasses. PEP 487 proposes a new metaclass which calls a method on all newly created subclasses. This way, in order to customize the creation of subclasses, one just needs to write a simple method. An absolutely classic example for metaclasses is the need to tell descriptors who they belong to. There are many large frameworks out there, e.g. enthought's traits, IPython's traitlets, Django's forms and many more. Their problem is: they're all fully incompatible. It's really hard to inherit from two classes which have different metaclasses. PEP 487 proposes to have one simple metaclass, which can do all those frameworks need, making them all compatible. As an example, imagine the framework has a generic descriptor called Integer, which describes, well, an integer. Typically you use it like that: class MyClass(FrameworkBaseClass): my_value = Integer() how does my_value know how it's called, how it should put its data into the object's __dict__? Well, this is what the framework's metaclass is for. With PEP 487, a framework doesn't need to declare an own metaclass anymore, but simply uses types.Object of PEP 487 as a base class: class FrameworkBaseClass(types.Object): def __init_subclass__(cls): super().__init_subclass__() for k, v in cls.__dict__.items(): if isinstance(v, FrameworkDescriptorBase): v.__set_owner__(cls, name) and all the framework's descriptors know their name. And if another framework should be used as well: no problem, they just work together easily. Actually, the above example is just that common, that PEP 487 includes it directly: a method __set_owner__ is called for every descriptor. That could make most descriptors in frameworks work out of the box. So now I am hoping for comments! Greetings Martin New version of the PEP follows: PEP: 487 Title: Simpler customisation of class creation Version: $Revision$ Last-Modified: $Date$ Author: Martin Teichmann <lkb.teichmann(a)gmail.com>, Status: Draft Type: Standards Track Content-Type: text/x-rst Created: 27-Feb-2015 Python-Version: 3.6 Post-History: 27-Feb-2015, 5-Feb-2016, 24-Jun-2016 Replaces: 422 Abstract ======== Currently, customising class creation requires the use of a custom metaclass. This custom metaclass then persists for the entire lifecycle of the class, creating the potential for spurious metaclass conflicts. This PEP proposes to instead support a wide range of customisation scenarios through a new ``__init_subclass__`` hook in the class body, a hook to initialize attributes. Those hooks should at first be defined in a metaclass in the standard library, with the option that this metaclass eventually becomes the default ``type`` metaclass. The new mechanism should be easier to understand and use than implementing a custom metaclass, and thus should provide a gentler introduction to the full power Python's metaclass machinery. Background ========== Metaclasses are a powerful tool to customize class creation. They have, however, the problem that there is no automatic way to combine metaclasses. If one wants to use two metaclasses for a class, a new metaclass combining those two needs to be created, typically manually. This need often occurs as a surprise to a user: inheriting from two base classes coming from two different libraries suddenly raises the necessity to manually create a combined metaclass, where typically one is not interested in those details about the libraries at all. This becomes even worse if one library starts to make use of a metaclass which it has not done before. While the library itself continues to work perfectly, suddenly every code combining those classes with classes from another library fails. Proposal ======== While there are many possible ways to use a metaclass, the vast majority of use cases falls into just three categories: some initialization code running after class creation, the initalization of descriptors and keeping the order in which class attributes were defined. Those three use cases can easily be performed by just one metaclass. If this metaclass is put into the standard library, and all libraries that wish to customize class creation use this very metaclass, no combination of metaclasses is necessary anymore. Said metaclass should live in the ``types`` module under the name ``Type``. This should hint the user that in the future, this metaclass may become the default metaclass ``type``. The three use cases are achieved as follows: 1. The metaclass contains an ``__init_subclass__`` hook that initializes all subclasses of a given class, 2. the metaclass calls a ``__set_owner__`` hook on all the attribute (descriptors) defined in the class, and For ease of use, a base class ``types.Object`` is defined, which uses said metaclass and contains an empty stub for the hook described for use case 1. It will eventually become the new replacement for the standard ``object``. As an example, the first use case looks as follows:: >>> class SpamBase(types.Object): ... # this is implicitly a @classmethod ... def __init_subclass__(cls, **kwargs): ... cls.class_args = kwargs ... super().__init_subclass__(cls, **kwargs) >>> class Spam(SpamBase, a=1, b="b"): ... pass >>> Spam.class_args {'a': 1, 'b': 'b'} The base class ``types.Object`` contains an empty ``__init_subclass__`` method which serves as an endpoint for cooperative multiple inheritance. Note that this method has no keyword arguments, meaning that all methods which are more specialized have to process all keyword arguments. This general proposal is not a new idea (it was first suggested for inclusion in the language definition `more than 10 years ago`_, and a similar mechanism has long been supported by `Zope's ExtensionClass`_), but the situation has changed sufficiently in recent years that the idea is worth reconsidering for inclusion. The second part of the proposal adds an ``__set_owner__`` initializer for class attributes, especially if they are descriptors. Descriptors are defined in the body of a class, but they do not know anything about that class, they do not even know the name they are accessed with. They do get to know their owner once ``__get__`` is called, but still they do not know their name. This is unfortunate, for example they cannot put their associated value into their object's ``__dict__`` under their name, since they do not know that name. This problem has been solved many times, and is one of the most important reasons to have a metaclass in a library. While it would be easy to implement such a mechanism using the first part of the proposal, it makes sense to have one solution for this problem for everyone. To give an example of its usage, imagine a descriptor representing weak referenced values:: import weakref class WeakAttribute: def __get__(self, instance, owner): return instance.__dict__[self.name] def __set__(self, instance, value): instance.__dict__[self.name] = weakref.ref(value) # this is the new initializer: def __set_owner__(self, owner, name): self.name = name While this example looks very trivial, it should be noted that until now such an attribute cannot be defined without the use of a metaclass. And given that such a metaclass can make life very hard, this kind of attribute does not exist yet. Key Benefits ============ Easier inheritance of definition time behaviour ----------------------------------------------- Understanding Python's metaclasses requires a deep understanding of the type system and the class construction process. This is legitimately seen as challenging, due to the need to keep multiple moving parts (the code, the metaclass hint, the actual metaclass, the class object, instances of the class object) clearly distinct in your mind. Even when you know the rules, it's still easy to make a mistake if you're not being extremely careful. Understanding the proposed implicit class initialization hook only requires ordinary method inheritance, which isn't quite as daunting a task. The new hook provides a more gradual path towards understanding all of the phases involved in the class definition process. Reduced chance of metaclass conflicts ------------------------------------- One of the big issues that makes library authors reluctant to use metaclasses (even when they would be appropriate) is the risk of metaclass conflicts. These occur whenever two unrelated metaclasses are used by the desired parents of a class definition. This risk also makes it very difficult to *add* a metaclass to a class that has previously been published without one. By contrast, adding an ``__init_subclass__`` method to an existing type poses a similar level of risk to adding an ``__init__`` method: technically, there is a risk of breaking poorly implemented subclasses, but when that occurs, it is recognised as a bug in the subclass rather than the library author breaching backwards compatibility guarantees. A path of introduction into Python ================================== Most of the benefits of this PEP can already be implemented using a simple metaclass. For the ``__init_subclass__`` hook this works all the way down to Python 2.7, while the attribute order needs Python 3.0 to work. Such a class has been `uploaded to PyPI`_. The only drawback of such a metaclass are the mentioned problems with metaclasses and multiple inheritance. Two classes using such a metaclass can only be combined, if they use exactly the same such metaclass. This fact calls for the inclusion of such a class into the standard library, as ``types.Type``, with a ``types.Object`` base class using it. Once all users use this standard library metaclass, classes from different packages can easily be combined. But still such classes cannot be easily combined with other classes using other metaclasses. Authors of metaclasses should bear that in mind and inherit from the standard metaclass if it seems useful for users of the metaclass to add more functionality. Ultimately, if the need for combining with other metaclasses is strong enough, the proposed functionality may be introduced into Python's ``type``. Those arguments strongly hint to the following procedure to include the proposed functionality into Python: 1. The metaclass implementing this proposal is put onto PyPI, so that it can be used and scrutinized. 2. Introduce this class into the Python 3.6 standard library. 3. Consider this as the default behavior for Python 3.7. Steps 2 and 3 would be similar to how the ``set`` datatype was first introduced as ``sets.Set``, and only later made a builtin type (with a slightly different API) based on wider experiences with the ``sets`` module. While the metaclass is still in the standard library and not in the language, it may still clash with other metaclasses. The most prominent metaclass in use is probably ABCMeta. It is also a particularly good example for the need of combining metaclasses. For users who want to define a ABC with subclass initialization, we should support a ``types.ABCMeta`` class, or let ``abc.ABCMeta`` inherit from this PEP's metaclass. As it turns out, most of the behavior of ``abc.ABCMeta`` can be done achieved with our ``types.Type``, except its core behavior, ``__instancecheck__`` and ``__subclasscheck__`` which can be supplied, as per the definition of the Python language, exclusively in a metaclass. Extensions written in C or C++ also often define their own metaclass. It would be very useful if those could also inherit from the metaclass defined here, but this is probably not possible. New Ways of Using Classes ========================= This proposal has many usecases like the following. In the examples, we still inherit from the ``SubclassInit`` base class. This would become unnecessary once this PEP is included in Python directly. Subclass registration --------------------- Especially when writing a plugin system, one likes to register new subclasses of a plugin baseclass. This can be done as follows:: class PluginBase(Object): subclasses = [] def __init_subclass__(cls, **kwargs): super().__init_subclass__(**kwargs) cls.subclasses.append(cls) In this example, ``PluginBase.subclasses`` will contain a plain list of all subclasses in the entire inheritance tree. One should note that this also works nicely as a mixin class. Trait descriptors ----------------- There are many designs of Python descriptors in the wild which, for example, check boundaries of values. Often those "traits" need some support of a metaclass to work. This is how this would look like with this PEP:: class Trait: def __get__(self, instance, owner): return instance.__dict__[self.key] def __set__(self, instance, value): instance.__dict__[self.key] = value def __set_owner__(self, owner, name): self.key = name Rejected Design Options ======================= Calling the hook on the class itself ------------------------------------ Adding an ``__autodecorate__`` hook that would be called on the class itself was the proposed idea of PEP 422. Most examples work the same way or even better if the hook is called on the subclass. In general, it is much easier to explicitly call the hook on the class in which it is defined (to opt-in to such a behavior) than to opt-out, meaning that one does not want the hook to be called on the class it is defined in. This becomes most evident if the class in question is designed as a mixin: it is very unlikely that the code of the mixin is to be executed for the mixin class itself, as it is not supposed to be a complete class on its own. The original proposal also made major changes in the class initialization process, rendering it impossible to back-port the proposal to older Python versions. More importantly, having a pure Python implementation allows us to take two preliminary steps before before we actually change the interpreter, giving us the chance to iron out all possible wrinkles in the API. Other variants of calling the hook ---------------------------------- Other names for the hook were presented, namely ``__decorate__`` or ``__autodecorate__``. This proposal opts for ``__init_subclass__`` as it is very close to the ``__init__`` method, just for the subclass, while it is not very close to decorators, as it does not return the class. Requiring an explicit decorator on ``__init_subclass__`` -------------------------------------------------------- One could require the explicit use of ``@classmethod`` on the ``__init_subclass__`` decorator. It was made implicit since there's no sensible interpretation for leaving it out, and that case would need to be detected anyway in order to give a useful error message. This decision was reinforced after noticing that the user experience of defining ``__prepare__`` and forgetting the ``@classmethod`` method decorator is singularly incomprehensible (particularly since PEP 3115 documents it as an ordinary method, and the current documentation doesn't explicitly say anything one way or the other). Defining arbitrary namespaces ----------------------------- PEP 422 defined a generic way to add arbitrary namespaces for class definitions. This approach is much more flexible than just leaving the definition order in a tuple. The ``__prepare__`` method in a metaclass supports exactly this behavior. But given that effectively the only use cases that could be found out in the wild were the ``OrderedDict`` way of determining the attribute order, it seemed reasonable to only support this special case. The metaclass described in this PEP has been designed to be very simple such that it could be reasonably made the default metaclass. This was especially important when designing the attribute order functionality: This was a highly demanded feature and has been enabled through the ``__prepare__`` method of metaclasses. This method can be abused in very weird ways, making it hard to correctly maintain this feature in CPython. This is why it has been proposed to deprecated this feature, and instead use ``OrderedDict`` as the standard namespace, supporting the most important feature while dropping most of the complexity. But this would have meant that ``OrderedDict`` becomes a language builtin like dict and set, and not just a standard library class. The choice of the ``__attribute_order__`` tuple is a much simpler solution to the problem. A more ``__new__``-like hook ---------------------------- In PEP 422 the hook worked more like the ``__new__`` method than the ``__init__`` method, meaning that it returned a class instead of modifying one. This allows a bit more flexibility, but at the cost of much harder implementation and undesired side effects. Adding a class attribute with the attribute order ------------------------------------------------- This got its own PEP 520. History ======= This used to be a competing proposal to PEP 422 by Nick Coghlan and Daniel Urban. PEP 422 intended to achieve the same goals as this PEP, but with a different way of implementation. In the meantime, PEP 422 has been withdrawn favouring this approach. References ========== .. _published code: http://mail.python.org/pipermail/python-dev/2012-June/119878.html .. _more than 10 years ago: http://mail.python.org/pipermail/python-dev/2001-November/018651.html .. _Zope's ExtensionClass: http://docs.zope.org/zope_secrets/extensionclass.html .. _uploaded to PyPI: https://pypi.python.org/pypi/metaclass Copyright ========= This document has been placed in the public domain. .. Local Variables: mode: indented-text indent-tabs-mode: nil sentence-end-double-space: t fill-column: 70 coding: utf-8 End:

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Summary of Python tracker Issues
by Python tracker 01 Jul '16

01 Jul '16

ACTIVITY SUMMARY (2016-06-24 - 2016-07-01) Python tracker at http://bugs.python.org/ To view or respond to any of the issues listed below, click on the issue. Do NOT respond to this message. Issues counts and deltas: open 5545 (+14) closed 33648 (+39) total 39193 (+53) Open issues with patches: 2421 Issues opened (39) ================== #22928: HTTP header injection in urrlib2/urllib/httplib/http.client (C http://bugs.python.org/issue22928 reopened by koobs #23804: SSLSocket.recv(0) receives up to 1024 bytes http://bugs.python.org/issue23804 reopened by martin.panter #27385: itertools.groupby has misleading doc string http://bugs.python.org/issue27385 opened by gmathews #27386: Asyncio server hang when clients connect and immediately disco http://bugs.python.org/issue27386 opened by j1m #27387: Thread hangs on str.encode() when locale is not set http://bugs.python.org/issue27387 opened by joshpurvis #27388: IDLE configdialog: reduce multiple references to Var names http://bugs.python.org/issue27388 opened by terry.reedy #27389: When a TypeError is raised due to invalid arguments to a metho http://bugs.python.org/issue27389 opened by Steven.Barker #27391: server_hostname should only be required when checking host nam http://bugs.python.org/issue27391 opened by j1m #27392: Add a server_side keyword parameter to create_connection http://bugs.python.org/issue27392 opened by j1m #27395: Increase test coverage of unittest.runner.TextTestResult http://bugs.python.org/issue27395 opened by Pam.McANulty #27397: email.message.Message.get_payload(decode=True) raises Assertio http://bugs.python.org/issue27397 opened by Claudiu Saftoiu #27398: configure warning for Python 3.5.2 during compilation http://bugs.python.org/issue27398 opened by wizzardx #27400: Datetime NoneType after calling Py_Finalize and Py_Initialize http://bugs.python.org/issue27400 opened by Denny Weinberg #27404: Misc/NEWS: add [Security] prefix to Python 3.5.2 changelog http://bugs.python.org/issue27404 opened by haypo #27405: Ability to trace Tcl commands executed by Tkinter http://bugs.python.org/issue27405 opened by serhiy.storchaka #27407: prepare_ssl.py missing in PCBuild folder http://bugs.python.org/issue27407 opened by George Ge #27408: Document importlib.abc.ExecutionLoader implements get_data() http://bugs.python.org/issue27408 opened by brett.cannon #27409: List socket.SO_*, SCM_*, MSG_*, IPPROTO_* symbols http://bugs.python.org/issue27409 opened by martin.panter #27410: DLL hijacking vulnerability in Python 3.5.2 installer http://bugs.python.org/issue27410 opened by anandbhat #27411: Possible different behaviour of explicit and implicit __dict__ http://bugs.python.org/issue27411 opened by xiang.zhang #27413: Add an option to json.tool to bypass non-ASCII characters. http://bugs.python.org/issue27413 opened by Wei-Cheng.Pan #27414: http.server.BaseHTTPRequestHandler inconsistence with Content- http://bugs.python.org/issue27414 opened by m.xhonneux #27415: BaseEventLoop.create_server does not accept port=None http://bugs.python.org/issue27415 opened by mcobden #27417: Call CoInitializeEx on startup http://bugs.python.org/issue27417 opened by steve.dower #27419: Bugs in PyImport_ImportModuleLevelObject http://bugs.python.org/issue27419 opened by serhiy.storchaka #27420: Docs for os.link - say what happens if link already exists http://bugs.python.org/issue27420 opened by python-bugs-uit #27422: Deadlock when mixing threading and multiprocessing http://bugs.python.org/issue27422 opened by Martin Ritter #27423: Failed assertions when running test.test_os on Windows http://bugs.python.org/issue27423 opened by ebarry #27424: Failures in test.test_logging http://bugs.python.org/issue27424 opened by ebarry #27425: Tests fail because of git's newline preferences on Windows http://bugs.python.org/issue27425 opened by ebarry #27426: Encoding mismatch causes some tests to fail on Windows http://bugs.python.org/issue27426 opened by ebarry #27427: Math tests http://bugs.python.org/issue27427 opened by franciscouzo #27428: Document WindowsRegistryFinder inherits from MetaPathFinder http://bugs.python.org/issue27428 opened by brett.cannon #27429: xml.sax.saxutils.escape doesn't escape multiple characters saf http://bugs.python.org/issue27429 opened by tylerjohnhughes #27432: Unittest truncating of error message not works http://bugs.python.org/issue27432 opened by Camilla Ke #27434: cross-building python 3.6 with an older interpreter fails http://bugs.python.org/issue27434 opened by xdegaye #27435: ctypes and AIX - also for 2.7.X (and later) http://bugs.python.org/issue27435 opened by aixtools(a)gmail.com #27436: Strange code in selectors.KqueueSelector http://bugs.python.org/issue27436 opened by dabeaz #1732367: Document the constants in the socket module http://bugs.python.org/issue1732367 reopened by martin.panter Most recent 15 issues with no replies (15) ========================================== #27436: Strange code in selectors.KqueueSelector http://bugs.python.org/issue27436 #27435: ctypes and AIX - also for 2.7.X (and later) http://bugs.python.org/issue27435 #27429: xml.sax.saxutils.escape doesn't escape multiple characters saf http://bugs.python.org/issue27429 #27428: Document WindowsRegistryFinder inherits from MetaPathFinder http://bugs.python.org/issue27428 #27427: Math tests http://bugs.python.org/issue27427 #27426: Encoding mismatch causes some tests to fail on Windows http://bugs.python.org/issue27426 #27420: Docs for os.link - say what happens if link already exists http://bugs.python.org/issue27420 #27411: Possible different behaviour of explicit and implicit __dict__ http://bugs.python.org/issue27411 #27409: List socket.SO_*, SCM_*, MSG_*, IPPROTO_* symbols http://bugs.python.org/issue27409 #27408: Document importlib.abc.ExecutionLoader implements get_data() http://bugs.python.org/issue27408 #27404: Misc/NEWS: add [Security] prefix to Python 3.5.2 changelog http://bugs.python.org/issue27404 #27395: Increase test coverage of unittest.runner.TextTestResult http://bugs.python.org/issue27395 #27388: IDLE configdialog: reduce multiple references to Var names http://bugs.python.org/issue27388 #27379: SocketType changed in Python 3 http://bugs.python.org/issue27379 #27376: Add mock_import method to mock module http://bugs.python.org/issue27376 Most recent 15 issues waiting for review (15) ============================================= #27427: Math tests http://bugs.python.org/issue27427 #27423: Failed assertions when running test.test_os on Windows http://bugs.python.org/issue27423 #27419: Bugs in PyImport_ImportModuleLevelObject http://bugs.python.org/issue27419 #27413: Add an option to json.tool to bypass non-ASCII characters. http://bugs.python.org/issue27413 #27409: List socket.SO_*, SCM_*, MSG_*, IPPROTO_* symbols http://bugs.python.org/issue27409 #27405: Ability to trace Tcl commands executed by Tkinter http://bugs.python.org/issue27405 #27404: Misc/NEWS: add [Security] prefix to Python 3.5.2 changelog http://bugs.python.org/issue27404 #27398: configure warning for Python 3.5.2 during compilation http://bugs.python.org/issue27398 #27395: Increase test coverage of unittest.runner.TextTestResult http://bugs.python.org/issue27395 #27385: itertools.groupby has misleading doc string http://bugs.python.org/issue27385 #27380: IDLE: add base Query dialog with ttk widgets http://bugs.python.org/issue27380 #27377: Add smarter socket.fromfd() http://bugs.python.org/issue27377 #27376: Add mock_import method to mock module http://bugs.python.org/issue27376 #27374: Cygwin: Makefile does not install DLL import library http://bugs.python.org/issue27374 #27369: [PATCH] Tests break with --with-system-expat and Expat 2.2.0 http://bugs.python.org/issue27369 Top 10 most discussed issues (10) ================================= #27364: Deprecate invalid unicode escape sequences http://bugs.python.org/issue27364 18 msgs #27417: Call CoInitializeEx on startup http://bugs.python.org/issue27417 18 msgs #27386: Asyncio server hang when clients connect and immediately disco http://bugs.python.org/issue27386 17 msgs #27392: Add a server_side keyword parameter to create_connection http://bugs.python.org/issue27392 15 msgs #23395: _thread.interrupt_main() errors if SIGINT handler in SIG_DFL, http://bugs.python.org/issue23395 12 msgs #26137: [idea] use the Microsoft Antimalware Scan Interface http://bugs.python.org/issue26137 11 msgs #27051: Create PIP gui http://bugs.python.org/issue27051 11 msgs #27391: server_hostname should only be required when checking host nam http://bugs.python.org/issue27391 10 msgs #26226: Test failures with non-ascii character in hostname on Windows http://bugs.python.org/issue26226 9 msgs #22079: Ensure in PyType_Ready() that base class of static type is sta http://bugs.python.org/issue22079 8 msgs Issues closed (39) ================== #4945: json checks True/False by identity, not boolean value http://bugs.python.org/issue4945 closed by serhiy.storchaka #18726: json functions have too many positional parameters http://bugs.python.org/issue18726 closed by serhiy.storchaka #19536: MatchObject should offer __getitem__() http://bugs.python.org/issue19536 closed by berker.peksag #20350: Replace tkapp.split() to tkapp.splitlist() http://bugs.python.org/issue20350 closed by serhiy.storchaka #20770: Inform caller of smtplib STARTTLS failures http://bugs.python.org/issue20770 closed by aclover #22115: Add new methods to trace Tkinter variables http://bugs.python.org/issue22115 closed by serhiy.storchaka #22890: StringIO.StringIO pickled in 2.7 is not unpickleable on 3.x http://bugs.python.org/issue22890 closed by serhiy.storchaka #23401: Add pickle support of Mapping views http://bugs.python.org/issue23401 closed by serhiy.storchaka #24833: IDLE tabnanny check fails http://bugs.python.org/issue24833 closed by terry.reedy #25042: Create an "embedding SDK" distribution? http://bugs.python.org/issue25042 closed by steve.dower #26186: LazyLoader rejecting use of SourceFileLoader http://bugs.python.org/issue26186 closed by brett.cannon #26664: Misuse of $ in activate.fish of venv http://bugs.python.org/issue26664 closed by brett.cannon #26721: Avoid socketserver.StreamRequestHandler.wfile doing partial wr http://bugs.python.org/issue26721 closed by martin.panter #27007: Alternate constructors bytes.fromhex() and bytearray.fromhex() http://bugs.python.org/issue27007 closed by serhiy.storchaka #27038: Make os.DirEntry exist http://bugs.python.org/issue27038 closed by brett.cannon #27252: Make dict views copyable http://bugs.python.org/issue27252 closed by serhiy.storchaka #27253: More efficient deepcopying of Mapping http://bugs.python.org/issue27253 closed by serhiy.storchaka #27255: More opcode predictions http://bugs.python.org/issue27255 closed by serhiy.storchaka #27352: Bug in IMPORT_NAME http://bugs.python.org/issue27352 closed by serhiy.storchaka #27365: Allow non-ascii chars in IDLE NEWS.txt (for contributor names) http://bugs.python.org/issue27365 closed by larry #27372: Test_idle should stop changing locale http://bugs.python.org/issue27372 closed by terry.reedy #27383: executuable in distutils triggering microsoft anti virus http://bugs.python.org/issue27383 closed by steve.dower #27384: itertools islice consumes items when given negative range http://bugs.python.org/issue27384 closed by rhettinger #27390: state of the 3.3 branch unclear http://bugs.python.org/issue27390 closed by brett.cannon #27393: Command to activate venv in Windows has wrong path http://bugs.python.org/issue27393 closed by berker.peksag #27394: Crash with compile returning a value with an error set http://bugs.python.org/issue27394 closed by ebarry #27396: Change default filecmp.cmp shallow option http://bugs.python.org/issue27396 closed by rhettinger #27399: ChainMap.keys() is broken http://bugs.python.org/issue27399 closed by Zahari.Dim #27401: Wrong FTP links in 3.5.2 installer http://bugs.python.org/issue27401 closed by zach.ware #27402: Sequence example in typing module documentation does not typec http://bugs.python.org/issue27402 closed by gvanrossum #27403: os.path.dirname doesn't handle Windows' URNs correctly http://bugs.python.org/issue27403 closed by eryksun #27406: subprocess.Popen() hangs in multi-threaded code http://bugs.python.org/issue27406 closed by r.david.murray #27412: float('∞') returns 8.0 http://bugs.python.org/issue27412 closed by eryksun #27416: typo / missing word in docs.python.org/2/library/copy.html http://bugs.python.org/issue27416 closed by haypo #27418: Tools/importbench/importbench.py is broken http://bugs.python.org/issue27418 closed by serhiy.storchaka #27421: PPC64LE Fedora 2.7: certificate for hg.python.org has unexpect http://bugs.python.org/issue27421 closed by haypo #27430: Spelling fixes http://bugs.python.org/issue27430 closed by berker.peksag #27431: Shelve pickle version error http://bugs.python.org/issue27431 closed by berker.peksag #27433: Missing "as err" in Lib/socket.py http://bugs.python.org/issue27433 closed by berker.peksag

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