| **************************** |
| What's New In Python 3.4 |
| **************************** |
| |
| .. :Author: Someone <email> |
| (uncomment if there is a principal author) |
| |
| .. Rules for maintenance: |
| |
| * Anyone can add text to this document, but the maintainer reserves the |
| right to rewrite any additions. In particular, for obscure or esoteric |
| features, the maintainer may reduce any addition to a simple reference to |
| the new documentation rather than explaining the feature inline. |
| |
| * While the maintainer will periodically go through Misc/NEWS |
| and add changes, it's best not to rely on this. We know from experience |
| that any changes that aren't in the What's New documentation around the |
| time of the original release will remain largely unknown to the community |
| for years, even if they're added later. We also know from experience that |
| other priorities can arise, and the maintainer will run out of time to do |
| updates - in such cases, end users will be much better served by partial |
| notifications that at least give a hint about new features to |
| investigate. |
| |
| * This is not a complete list of every single change; completeness |
| is the purpose of Misc/NEWS. The What's New should focus on changes that |
| are visible to Python *users* and that *require* a feature release (i.e. |
| most bug fixes should only be recorded in Misc/NEWS) |
| |
| * PEPs should not be marked Final until they have an entry in What's New. |
| A placeholder entry that is just a section header and a link to the PEP |
| (e.g ":pep:`397` has been implemented") is acceptable. If a PEP has been |
| implemented and noted in What's New, don't forget to mark it as Final! |
| |
| * If you want to draw your new text to the attention of the |
| maintainer, add 'XXX' to the beginning of the paragraph or |
| section. |
| |
| * It's OK to add just a very brief note about a change. For |
| example: "The :ref:`~socket.transmogrify()` function was added to the |
| :mod:`socket` module." The maintainer will research the change and |
| write the necessary text (if appropriate). The advantage of doing this |
| is that even if no more descriptive text is ever added, readers will at |
| least have a notification that the new feature exists and a link to the |
| relevant documentation. |
| |
| * You can comment out your additions if you like, but it's not |
| necessary (especially when a final release is some months away). |
| |
| * Credit the author of a patch or bugfix. Just the name is |
| sufficient; the e-mail address isn't necessary. |
| |
| * It's helpful to add the bug/patch number as a comment: |
| |
| The :ref:`~socket.transmogrify()` function was added to the |
| :mod:`socket` module. (Contributed by P.Y. Developer in :issue:`12345`.) |
| |
| This saves the maintainer the effort of going through the Mercurial log |
| when researching a change. |
| |
| * Cross referencing tip: :ref:`mod.attr` will display as ``mod.attr``, |
| while :ref:`~mod.attr` will display as ``attr``. |
| |
| This article explains the new features in Python 3.4, compared to 3.3. |
| |
| .. Python 3.4 was released on TBD. |
| |
| For full details, see the |
| `changelog <http://docs.python.org/3.4/whatsnew/changelog.html>`_. |
| |
| .. note:: Prerelease users should be aware that this document is currently in |
| draft form. It will be updated substantially as Python 3.4 moves towards |
| release, so it's worth checking back even after reading earlier versions. |
| |
| |
| .. seealso:: |
| |
| .. :pep:`4XX` - Python 3.4 Release Schedule |
| |
| |
| Summary -- Release highlights |
| ============================= |
| |
| .. This section singles out the most important changes in Python 3.4. |
| Brevity is key. |
| |
| New syntax features: |
| |
| * None yet. |
| |
| New library modules: |
| |
| * :mod:`enum`: Implementation of the :pep:`435`. |
| * :mod:`selectors`: High-level and efficient I/O multiplexing, built upon the |
| :mod:`select` module primitives. |
| |
| New built-in features: |
| |
| * :ref:`PEP 442: Safe object finalization <pep-442>`. |
| * :ref:`PEP 445: Configurable memory allocators <pep-445>`. |
| * :ref:`PEP 446: Make newly created file descriptors non-inheritable <pep-446>`. |
| |
| Implementation improvements: |
| |
| * A more efficient :mod:`marshal` format (:issue:`16475`). |
| * Improve finalization of Python modules to avoid setting their globals |
| to None, in most cases (:issue:`18214`). |
| |
| Significantly Improved Library Modules: |
| |
| * Single-dispatch generic functions (:pep:`443`) |
| * SHA-3 (Keccak) support for :mod:`hashlib`. |
| * TLSv1.1 and TLSv1.2 support for :mod:`ssl`. |
| * :mod:`multiprocessing` now has option to avoid using :func:`os.fork` |
| on Unix (:issue:`8713`). |
| |
| Security improvements: |
| |
| * command line option for :ref:`isolated mode <using-on-misc-options>`, |
| :issue:`16499`. |
| |
| Please read on for a comprehensive list of user-facing changes. |
| |
| .. _pep-446: |
| |
| PEP 446: Make newly created file descriptors non-inheritable |
| ============================================================ |
| |
| The :pep:`446` makes newly created file descriptors :ref:`non-inheritable |
| <fd_inheritance>`. New functions and methods: |
| |
| * :func:`os.get_inheritable`, :func:`os.set_inheritable` |
| * :func:`os.get_handle_inheritable`, :func:`os.set_handle_inheritable` |
| * :meth:`socket.socket.get_inheritable`, :meth:`socket.socket.set_inheritable` |
| |
| |
| .. _pep-445: |
| |
| PEP 445: Add new APIs to customize Python memory allocators |
| =========================================================== |
| |
| The :pep:`445` adds new Application Programming Interfaces (API) to customize |
| Python memory allocators. |
| |
| |
| .. _pep-442: |
| |
| PEP 442: Safe object finalization |
| ================================= |
| |
| This PEP removes the current limitations and quirks of object finalization. |
| With it, objects with :meth:`__del__` methods, as well as generators |
| with :keyword:`finally` clauses, can be finalized when they are part of a |
| reference cycle. |
| |
| As part of this change, module globals are no longer forcibly set to |
| :const:`None` during interpreter shutdown, instead relying on the normal |
| operation of the cyclic garbage collector. |
| |
| .. seealso:: |
| |
| :pep:`442` - Safe object finalization |
| PEP written and implemented by Antoine Pitrou |
| |
| |
| Other Language Changes |
| ====================== |
| |
| Some smaller changes made to the core Python language are: |
| |
| * Unicode database updated to UCD version 6.3. |
| |
| * :func:`min` and :func:`max` now accept a *default* argument that can be used |
| to specify the value they return if the iterable they are evaluating has no |
| elements. Contributed by Julian Berman in :issue:`18111`. |
| |
| * Module objects are now :mod:`weakref`'able. |
| |
| |
| New Modules |
| =========== |
| |
| selectors |
| --------- |
| |
| The new :mod:`selectors` module allows high-level and efficient I/O |
| multiplexing, built upon the :mod:`select` module primitives. |
| |
| |
| Improved Modules |
| ================ |
| |
| aifc |
| ---- |
| |
| The :meth:`~aifc.getparams` method now returns a namedtuple rather than a |
| plain tuple. (Contributed by Claudiu Popa in :issue:`17818`.) |
| |
| |
| codecs |
| ------ |
| |
| The :meth:`codecs.encode` and :meth:`codecs.decode` convenience functions are |
| now properly documented. These functions have existed in the :mod:`codecs` |
| module since ~2004, but were previously only discoverable through runtime |
| introspection. |
| |
| Unlike the convenience methods on :class:`str`, :class:`bytes` and |
| :class:`bytearray`, these convenience functions support arbitrary codecs, |
| rather than being limited to Unicode text encodings. |
| |
| |
| colorsys |
| -------- |
| |
| The number of digits in the coefficients for the RGB --- YIQ conversions have |
| been expanded so that they match the FCC NTSC versions. The change in |
| results should be less than 1% and may better match results found elsewhere. |
| |
| |
| contextlib |
| ---------- |
| |
| The new :class:`contextlib.suppress` context manager helps to clarify the |
| intent of code that deliberately suppresses exceptions from a single |
| statement. (Contributed by Raymond Hettinger in :issue:`15806` and |
| Zero Piraeus in :issue:`19266`) |
| |
| |
| The new :class:`contextlib.redirect_stdio` context manager makes it easier |
| for utility scripts to handle inflexible APIs that don't provide any |
| options to retrieve their output as a string or direct it to somewhere |
| other than :data:`sys.stdout`. (Contribute by Raymond Hettinger in |
| :issue:`15805`) |
| |
| |
| dis |
| --- |
| |
| The :mod:`dis` module is now built around an :class:`~dis.Instruction` class |
| that provides details of individual bytecode operations and a |
| :func:`~dis.get_instructions` iterator that emits the Instruction stream for a |
| given piece of Python code. The various display tools in the :mod:`dis` |
| module have been updated to be based on these new components. |
| |
| The new :class:`dis.Bytecode` class provides an object-oriented API for |
| inspecting bytecode, both in human-readable form and for iterating over |
| instructions. |
| |
| (Contributed by Nick Coghlan, Ryan Kelly and Thomas Kluyver in :issue:`11816`) |
| |
| |
| doctest |
| ------- |
| |
| Added :data:`~doctest.FAIL_FAST` flag to halt test running as soon as the first |
| failure is detected. (Contributed by R. David Murray and Daniel Urban in |
| :issue:`16522`.) |
| |
| Updated the doctest command line interface to use :mod:`argparse`, and added |
| ``-o`` and ``-f`` options to the interface. ``-o`` allows doctest options to |
| be specified on the command line, and ``-f`` is a shorthand for ``-o |
| FAIL_FAST`` (to parallel the similar option supported by the :mod:`unittest` |
| CLI). (Contributed by R. David Murray in :issue:`11390`.) |
| |
| |
| email |
| ----- |
| |
| :meth:`~email.message.Message.as_string` now accepts a *policy* argument to |
| override the default policy of the message when generating a string |
| representation of it. This means that ``as_string`` can now be used in more |
| circumstances, instead of having to create and use a :mod:`~email.generator` in |
| order to pass formatting parameters to its ``flatten`` method. |
| |
| New method :meth:`~email.message.Message.as_bytes` added to produce a bytes |
| representation of the message in a fashion similar to how ``as_string`` |
| produces a string representation. It does not accept the *maxheaderlen* |
| argument, but does accept the *unixfrom* and *policy* arguments. The |
| :class:`~email.message.Message` :meth:`~email.message.Message.__bytes__` method |
| calls it, meaning that ``bytes(mymsg)`` will now produce the intuitive |
| result: a bytes object containing the fully formatted message. |
| |
| (Contributed by R. David Murray in :issue:`18600`.) |
| |
| A pair of new subclasses of :class:`~email.message.Message` have been added, |
| along with a new sub-module, :mod:`~email.contentmanager`. All documentation |
| is currently in the new module, which is being added as part of the new |
| :term:`provisional <provisional package>` email API. These classes provide a |
| number of new methods that make extracting content from and inserting content |
| into email messages much easier. See the :mod:`~email.contentmanager` |
| documentation for details. |
| |
| These API additions complete the bulk of the work that was planned as part of |
| the email6 project. The currently provisional API is scheduled to become final |
| in Python 3.5 (possibly with a few minor additions in the area of error |
| handling). |
| |
| (Contributed by R. David Murray in :issue:`18891`.) |
| |
| |
| functools |
| --------- |
| |
| New :func:`functools.singledispatch` decorator: see the :pep:`443`. |
| |
| |
| hashlib |
| ------- |
| |
| New :func:`hashlib.pbkdf2_hmac` function. |
| |
| (Contributed by Christian Heimes in :issue:`18582`) |
| |
| |
| inspect |
| ------- |
| |
| |
| The inspect module now offers a basic command line interface to quickly |
| display source code and other information for modules, classes and |
| functions. |
| |
| :func:`~inspect.unwrap` makes it easy to unravel wrapper function chains |
| created by :func:`functools.wraps` (and any other API that sets the |
| ``__wrapped__`` attribute on a wrapper function). |
| |
| mmap |
| ---- |
| |
| mmap objects can now be weakref'ed. |
| |
| (Contributed by Valerie Lambert in :issue:`4885`.) |
| |
| |
| multiprocessing |
| --------------- |
| |
| On Unix two new *start methods* have been added for starting processes |
| using :mod:`multiprocessing`. These make the mixing of processes with |
| threads more robust. See :issue:`8713`. |
| |
| Also, except when using the old *fork* start method, child processes |
| will no longer inherit unneeded handles/file descriptors from their parents. |
| |
| |
| os |
| -- |
| |
| New functions to get and set the :ref:`inheritable flag <fd_inheritance>` of a file |
| descriptors or a Windows handle: |
| |
| * :func:`os.get_inheritable`, :func:`os.set_inheritable` |
| * :func:`os.get_handle_inheritable`, :func:`os.set_handle_inheritable` |
| |
| |
| pdb |
| --- |
| |
| The ``print`` command has been removed from :mod:`pdb`, restoring access to the |
| ``print`` function. |
| |
| Rationale: Python2's ``pdb`` did not have a ``print`` command; instead, |
| entering ``print`` executed the ``print`` statement. In Python3 ``print`` was |
| mistakenly made an alias for the pdb :pdbcmd:`p` command. ``p``, however, |
| prints the ``repr`` of its argument, not the ``str`` like the Python2 ``print`` |
| command did. Worse, the Python3 ``pdb print`` command shadowed the Python3 |
| ``print`` function, making it inaccessible at the ``pdb`` prompt. |
| |
| (Contributed by Connor Osborn in :issue:`18764`.) |
| |
| |
| poplib |
| ------ |
| |
| New :meth:`~poplib.POP3.stls` method to switch a clear-text POP3 session into |
| an encrypted POP3 session. |
| |
| New :meth:`~poplib.POP3.capa` method to query the capabilities advertised by the |
| POP3 server. |
| |
| (Contributed by Lorenzo Catucci in :issue:`4473`.) |
| |
| |
| pprint |
| ------ |
| |
| The :mod::`pprint` module now supports *compact* mode for formatting long |
| sequences (:issue:`19132`). |
| |
| |
| smtplib |
| ------- |
| |
| :exc:`~smtplib.SMTPException` is now a subclass of :exc:`OSError`, which allows |
| both socket level errors and SMTP protocol level errors to be caught in one |
| try/except statement by code that only cares whether or not an error occurred. |
| (:issue:`2118`). |
| |
| |
| socket |
| ------ |
| |
| Socket objects have new methods to get or set their :ref:`inheritable flag |
| <fd_inheritance>`: |
| |
| * :meth:`socket.socket.get_inheritable`, :meth:`socket.socket.set_inheritable` |
| |
| The ``socket.AF_*`` and ``socket.SOCK_*`` constants are enumeration values, |
| using the new :mod:`enum` module. This allows descriptive reporting during |
| debugging, instead of seeing integer "magic numbers". |
| |
| ssl |
| --- |
| |
| TLSv1.1 and TLSv1.2 support. |
| |
| (Contributed by Michele Orrù and Antoine Pitrou in :issue:`16692`) |
| |
| * New diagnostic functions :func:`~ssl.get_default_verify_paths`, |
| :meth:`~ssl.SSLContext.cert_store_stats` and |
| :meth:`~ssl.SSLContext.get_ca_certs` |
| |
| * Add :func:`ssl.enum_cert_store` to retrieve certificates and CRL from Windows' |
| cert store. |
| |
| (Contributed by Christian Heimes in :issue:`18143`, :issue:`18147` and |
| :issue:`17134`.) |
| |
| Support for server-side SNI using the new |
| :meth:`ssl.SSLContext.set_servername_callback` method. |
| |
| (Contributed by Daniel Black in :issue:`8109`.) |
| |
| |
| stat |
| ---- |
| |
| The :mod:`stat` module is now backed by a C implementation in :mod:`_stat`. A C |
| implementation is required as most of the values aren't standardized and |
| platform-dependent. (Contributed by Christian Heimes in :issue:`11016`.) |
| |
| The module supports new file types: door, event port and whiteout. |
| |
| |
| struct |
| ------ |
| |
| Streaming struct unpacking using :func:`struct.iter_unpack`. |
| |
| (Contributed by Antoine Pitrou in :issue:`17804`.) |
| |
| |
| sunau |
| ----- |
| |
| The :meth:`~sunau.getparams` method now returns a namedtuple rather than a |
| plain tuple. (Contributed by Claudiu Popa in :issue:`18901`.) |
| |
| :meth:`sunau.open` now supports the context manager protocol (:issue:`18878`). |
| |
| |
| traceback |
| --------- |
| |
| A new :func:`traceback.clear_frames` function takes a traceback object |
| and clears the local variables in all of the frames it references, |
| reducing the amount of memory consumed (:issue:`1565525`). |
| |
| |
| urllib |
| ------ |
| |
| Add support.for ``data:`` URLs in :mod:`urllib.request`. |
| |
| (Contributed by Mathias Panzenböck in :issue:`16423`.) |
| |
| |
| unittest |
| -------- |
| |
| Support for easy dynamically-generated subtests using the |
| :meth:`~unittest.TestCase.subTest` context manager. |
| |
| (Contributed by Antoine Pitrou in :issue:`16997`.) |
| |
| |
| wave |
| ---- |
| |
| The :meth:`~wave.getparams` method now returns a namedtuple rather than a |
| plain tuple. (Contributed by Claudiu Popa in :issue:`17487`.) |
| |
| :meth:`wave.open` now supports the context manager protocol. (Contributed |
| by Claudiu Popa in :issue:`17616`.) |
| |
| |
| weakref |
| ------- |
| |
| New :class:`~weakref.WeakMethod` class simulates weak references to bound |
| methods. (Contributed by Antoine Pitrou in :issue:`14631`.) |
| |
| New :class:`~weakref.finalize` class makes it possible to register a callback |
| to be invoked when an object is garbage collected, without needing to |
| carefully manage the lifecycle of the weak reference itself. (Contributed by |
| Richard Oudkerk in :issue:`15528`) |
| |
| |
| xml.etree |
| --------- |
| |
| Add an event-driven parser for non-blocking applications, |
| :class:`~xml.etree.ElementTree.XMLPullParser`. |
| |
| (Contributed by Antoine Pitrou in :issue:`17741`.) |
| |
| Other improvements |
| ================== |
| |
| Tab-completion is now enabled by default in the interactive interpreter. |
| |
| (Contributed by Antoine Pitrou and Éric Araujo in :issue:`5845`.) |
| |
| Python invocation changes |
| ========================= |
| |
| Invoking the Python interpreter with ``--version`` now outputs the version to |
| standard output instead of standard error (:issue:`18338`). Similar changes |
| were made to :mod:`argparse` (:issue:`18920`) and other modules that have |
| script-like invocation capabilities (:issue:`18922`). |
| |
| Optimizations |
| ============= |
| |
| Major performance enhancements have been added: |
| |
| * The UTF-32 decoder is now 3x to 4x faster. |
| |
| * The cost of hash collisions for sets is now reduced. Each hash table |
| probe now checks a series of consecutive, adjacent key/hash pairs before |
| continuing to make random probes through the hash table. This exploits |
| cache locality to make collision resolution less expensive. |
| |
| The collision resolution scheme can be described as a hybrid of linear |
| probing and open addressing. The number of additional linear probes |
| defaults to nine. This can be changed at compile-time by defining |
| LINEAR_PROBES to be any value. Set LINEAR_PROBES=0 to turn-off |
| linear probing entirely. |
| |
| (Contributed by Raymond Hettinger in :issue"`18771`.) |
| |
| * The interpreter starts about 30% faster. A couple of measures lead to the |
| speedup. The interpreter loads fewer modules on startup, e.g. the :mod:`re`, |
| :mod:`collections` and :mod:`locale` modules and their dependencies are no |
| longer imported by default. The marshal module has been improved to load |
| compiled Python code faster. |
| |
| (Contributed by Antoine Pitrou, Christian Heimes and Victor Stinner in |
| :issue:`19219`, :issue:`19218`, :issue:`19209`, :issue:`19205` and |
| :issue:`9548`) |
| |
| |
| |
| Build and C API Changes |
| ======================= |
| |
| Changes to Python's build process and to the C API include: |
| |
| * The new :c:func:`Py_SetStandardStreamEncoding` pre-initialization API |
| allows applications embedding the CPython interpreter to reliably force |
| a particular encoding and error handler for the standard streams |
| (Contributed by Bastien Montagne and Nick Coghlan in :issue:`16129`) |
| |
| |
| Deprecated |
| ========== |
| |
| Unsupported Operating Systems |
| ----------------------------- |
| |
| * OS/2 |
| * Windows 2000 |
| |
| |
| Deprecated Python modules, functions and methods |
| ------------------------------------------------ |
| |
| * :meth:`difflib.SequenceMatcher.isbjunk` and |
| :meth:`difflib.SequenceMatcher.isbpopular` were removed: use ``x in sm.bjunk`` and |
| ``x in sm.bpopular``, where *sm* is a :class:`~difflib.SequenceMatcher` object. |
| |
| * :func:`importlib.util.module_for_loader` is pending deprecation. Using |
| :func:`importlib.util.module_to_load` and |
| :meth:`importlib.abc.Loader.init_module_attrs` allows subclasses of a loader |
| to more easily customize module loading. |
| |
| * The :mod:`imp` module is pending deprecation. To keep compatibility with |
| Python 2/3 code bases, the module's removal is currently not scheduled. |
| |
| * The :mod:`formatter` module is pending deprecation and is slated for removal |
| in Python 3.6. |
| |
| |
| Deprecated functions and types of the C API |
| ------------------------------------------- |
| |
| * The ``PyThreadState.tick_counter`` field has been value: its value was meaningless |
| since Python 3.2 ("new GIL"). |
| |
| |
| Deprecated features |
| ------------------- |
| |
| * None yet. |
| |
| |
| Porting to Python 3.4 |
| ===================== |
| |
| This section lists previously described changes and other bugfixes |
| that may require changes to your code. |
| |
| * The ABCs defined in :mod:`importlib.abc` now either raise the appropriate |
| exception or return a default value instead of raising |
| :exc:`NotImplementedError` blindly. This will only affect code calling |
| :func:`super` and falling through all the way to the ABCs. For compatibility, |
| catch both :exc:`NotImplementedError` or the appropriate exception as needed. |
| |
| * The module type now initializes the :attr:`__package__` and :attr:`__loader__` |
| attributes to ``None`` by default. To determine if these attributes were set |
| in a backwards-compatible fashion, use e.g. |
| ``getattr(module, '__loader__', None) is not None``. |
| |
| * :meth:`importlib.util.module_for_loader` now sets ``__loader__`` and |
| ``__package__`` unconditionally to properly support reloading. If this is not |
| desired then you will need to set these attributes manually. You can use |
| :func:`importlib.util.module_to_load` for module management. |
| |
| * Import now resets relevant attributes (e.g. ``__name__``, ``__loader__``, |
| ``__package__``, ``__file__``, ``__cached__``) unconditionally when reloading. |
| |
| * Frozen packages no longer set ``__path__`` to a list containing the package |
| name but an empty list instead. Determing if a module is a package should be |
| done using ``hasattr(module, '__path__')``. |
| |
| * :c:func:`PyErr_SetImportError` now sets :exc:`TypeError` when its **msg** |
| argument is not set. Previously only ``NULL`` was returned with no exception |
| set. |
| |
| * :func:`py_compile.compile` now raises :exc:`FileExistsError` if the file path |
| it would write to is a symlink or a non-regular file. This is to act as a |
| warning that import will overwrite those files with a regular file regardless |
| of what type of file path they were originally. |
| |
| * :meth:`importlib.abc.SourceLoader.get_source` no longer raises |
| :exc:`ImportError` when the source code being loaded triggers a |
| :exc:`SyntaxError` or :exc:`UnicodeDecodeError`. As :exc:`ImportError` is |
| meant to be raised only when source code cannot be found but it should, it was |
| felt to be over-reaching/overloading of that meaning when the source code is |
| found but improperly structured. If you were catching ImportError before and |
| wish to continue to ignore syntax or decoding issues, catch all three |
| exceptions now. |
| |
| * :func:`functools.update_wrapper` and :func:`functools.wraps` now correctly |
| set the ``__wrapped__`` attribute even if the wrapped function had a |
| wrapped attribute set. This means ``__wrapped__`` attributes now correctly |
| link a stack of decorated functions rather than every ``__wrapped__`` |
| attribute in the chain referring to the innermost function. Introspection |
| libraries that assumed the previous behaviour was intentional can use |
| :func:`inspect.unwrap` to gain equivalent behaviour. |
| |
| * (C API) The result of the :c:data:`PyOS_ReadlineFunctionPointer` callback must |
| now be a string allocated by :c:func:`PyMem_RawMalloc` or |
| :c:func:`PyMem_RawRealloc`, or *NULL* if an error occurred, instead of a |
| string allocated by :c:func:`PyMem_Malloc` or :c:func:`PyMem_Realloc`. |
| |
| * :cls:`importlib.machinery.PathFinder` now passes on the current working |
| directory to objects in :data:`sys.path_hooks` for the empty string. This |
| results in :data:`sys.path_importer_cache` never containing ``''``, thus |
| iterating through :data:`sys.path_importer_cache` based on :data:`sys.path` |
| will not find all keys. A module's ``__file__`` when imported in the current |
| working directory will also now have an absolute path, including when using |
| ``-m`` with the interpreter (this does not influence when the path to a file |
| is specified on the command-line). |
| |
| * :cls:`importlib.machinery.FileFinder` no longer special-cases the empty string |
| to be changed to ``'.'``. |