### Navigation

- index
- modules |
- next |
- previous |
- Python »
- 3.6.0a0 Documentation »
- What’s New in Python »

# What’s New In Python 3.5

Release: | 3.6.0a0
Date: | August 24, 2015

This article explains the new features in Python 3.5, compared to 3.4.

For full details, see the Misc/NEWS file.

Note

Prerelease users should be aware that this document is currently in draft form. It will be updated substantially as Python 3.5 moves towards release, so it’s worth checking back even after reading earlier versions.

See also

PEP 478 - Python 3.5 Release Schedule

## Summary – Release highlights

New syntax features:

- PEP 465, a new matrix multiplication operator: `a @ b`.
- PEP 492, coroutines with async and await syntax.
- PEP 448, additional unpacking generalizations.

New library modules:

- `zipapp`: Improving Python ZIP Application Support (PEP 441).

New built-in features:

- `bytes % args`, `bytearray % args`: PEP 461 - Adding `%` formatting to bytes and bytearray
- `b'\xf0\x9f\x90\x8d'.hex()`, `bytearray(b'\xf0\x9f\x90\x8d').hex()`, `memoryview(b'\xf0\x9f\x90\x8d').hex()`: issue 9951 - A `hex` method has been added to bytes, bytearray, and memoryview.
- Generators have new `gi_yieldfrom` attribute, which returns the object being iterated by `yield from` expressions. (Contributed by Benno Leslie and Yury Selivanov in issue 24450.)
- New `RecursionError` exception. (Contributed by Georg Brandl in issue 19235.)

Implementation improvements:

- When the `LC_TYPE` locale is the POSIX locale (`C` locale), `sys.stdin` and `sys.stdout` are now using the `surrogateescape` error handler, instead of the `strict` error handler (issue 19977).
- PEP 488, the elimination of `.pyo` files.
- PEP 489, multi-phase initialization of extension modules.

Significantly Improved Library Modules:

- `collections.OrderedDict` is now implemented in C, which improves its performance between 4x to 100x times. Contributed by Eric Snow in issue 16991.
- You may now pass bytes to the `tempfile` module’s APIs and it will return the temporary pathname as bytes instead of str. It also accepts a value of `None` on parameters where only str was accepted in the past to do the right thing based on the types of the other inputs. Two functions, `gettempdirb()` and `gettempprefixb()`, have been added to go along with this. This behavior matches that of the `os` APIs.
- `ssl` module gained support for Memory BIO, which decouples SSL protocol handling from network IO. (Contributed by Geert Jansen in issue 21965.)

Security improvements:

- None yet.

Windows improvements:

- A new installer for Windows has replaced the old MSI. See Using Python on Windows for more information.
- Windows builds now use Microsoft Visual C++ 14.0, and extension modules should use the same.

Please read on for a comprehensive list of user-facing changes.

### PEP 492 - Coroutines with async and await syntax

The PEP added dedicated syntax for declaring coroutines, `await` expressions, new asynchronous `async for` and `async with` statements.

Example:

    async def read_data(db):
        async with db.transaction():
            data = await db.fetch('SELECT ...')

PEP written and implemented by Yury Selivanov.

See also

PEP 492 – Coroutines with async and await syntax

### PEP 461 - Formatting support for bytes and bytearray

This PEP proposes adding % formatting operations similar to Python 2’s `str` type to `bytes` and `bytearray`.

Examples:

    >>> b'Hello %s!' % b'World'
    b'Hello World!'
    >>> b'x=%i y=%f' % (1, 2.5)
    b'x=1 y=2.500000'

Unicode is not allowed for `%s`, but it is accepted by `%a` (equivalent of `repr(obj).encode('ascii', 'backslashreplace')`):

    >>> b'Hello %s!' % 'World'
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: %b requires bytes, or an object that implements __bytes__, not 'str'
    >>> b'price: %a' % '10€'
    b"price: '10\\u20ac'"

See also

PEP 461 – Adding % formatting to bytes and bytearray

### PEP 465 - A dedicated infix operator for matrix multiplication

This PEP proposes a new binary operator to be used for matrix multiplication, called `@`. (Mnemonic: `@` is `*` for mATrices.)

See also

PEP 465 – A dedicated infix operator for matrix multiplication

### PEP 448 - Additional Unpacking Generalizations

This PEP proposes extended usages of the `*` iterable unpacking operator and `**` dictionary unpacking operators to allow unpacking in more positions, an arbitrary number of times, and in additional circumstances. Specifically, in function calls, in comprehensions and generator expressions, and in displays.

Function calls are proposed to support an arbitrary number of unpackings rather than just one:

    >>> print(*[1], *[2], 3)
    1 2 3
    >>> dict(**{'x': 1}, y=2, **{'z': 3})
    {'x': 1, 'y': 2, 'z': 3}

Unpacking is proposed to be allowed inside tuple, list, set, and dictionary displays:

    >>> *range(4), 4
    (0, 1, 2, 3, 4)
    >>> [*range(4), 4]
    [0, 1, 2, 3, 4]
    >>> {*range(4), 4}
    {0, 1, 2, 3, 4}
    >>> {'x': 1, **{'y': 2}}
    {'x': 1, 'y': 2}

In dictionaries, later values will always override earlier ones:

    >>> {'x': 1, **{'x': 2}}
    {'x': 2}

    >>> {**{'x': 2}, 'x': 1}
    {'x': 1}

See also

PEP 448 – Additional Unpacking Generalizations

### PEP 484 - Type Hints

This PEP introduces a provisional module to provide these standard definitions and tools, along with some conventions for situations where annotations are not available.

For example, here is a simple function whose argument and return type are declared in the annotations:

    def greeting(name: str) -> str:
        return 'Hello ' + name

The type system supports unions, generic types, and a special type named `Any` which is consistent with (i.e. assignable to and from) all types.

See also

- PEP 484 – Type Hints
- `typing` module documentation

### PEP 471 - os.scandir() function – a better and faster directory iterator

PEP 471 adds a new directory iteration function, `os.scandir()`, to the standard library. Additionally, `os.walk()` is now implemented using `os.scandir()`, which speeds it up by 3-5 times on POSIX systems and by 7-20 times on Windows systems.

PEP and implementation written by Ben Hoyt with the help of Victor Stinner.

See also

PEP 471 – os.scandir() function – a better and faster directory iterator

### PEP 475: Retry system calls failing with EINTR

PEP 475 adds support for automatic retry of system calls failing with `EINTR`: this means that user code doesn’t have to deal with EINTR or `InterruptedError` manually, and should make it more robust against asynchronous signal reception.

Examples of functions which are now retried when interrupted by a signal instead of raising `InterruptedError` if the Python signal handler does not raise an exception:

- `open()`, `os.open()`, `io.open()`
- functions of the `faulthandler` module
- `os` functions:
  - `os.fchdir()`
  - `os.fchmod()`
  - `os.fchown()`
  - `os.fdatasync()`
  - `os.fstat()`
  - `os.fstatvfs()`
  - `os.fsync()`
  - `os.ftruncate()`
  - `os.mkfifo()`
  - `os.mknod()`
  - `os.posix_fadvise()`
  - `os.posix_fallocate()`
  - `os.pread()`
  - `os.pwrite()`
  - `os.read()`
  - `os.readv()`
  - `os.sendfile()`
  - `os.wait3()`
  - `os.wait4()`
  - `os.wait()`
  - `os.waitid()`
  - `os.waitpid()`
  - `os.write()`
  - `os.writev()`
  - special cases: `os.close()` and `os.dup2()` now ignore `EINTR` error, the syscall is not retried (see the PEP for the rationale)
- `select` functions:
  - `select.devpoll.poll()`
  - `select.epoll.poll()`
  - `select.kqueue.control()`
  - `select.poll.poll()`
  - `select.select()`
- `socket.socket()` methods:
  - `accept()`
  - `connect()` (except for non-blocking sockets)
  - `recv()`
  - `recvfrom()`
  - `recvmsg()`
  - `send()`
  - `sendall()`
  - `sendmsg()`
  - `sendto()`
- `signal.sigtimedwait()`, `signal.sigwaitinfo()`
- `time.sleep()`

PEP and implementation written by Charles-François Natali and Victor Stinner, with the help of Antoine Pitrou (the french connection).

See also

PEP 475 – Retry system calls failing with EINTR

### PEP 479: Change StopIteration handling inside generators

PEP 479 changes the behavior of generators: when a `StopIteration` exception is raised inside a generator, it is replaced with a `RuntimeError`. To enable the feature a `__future__` import should be used:

    from __future__ import generator_stop

Without a `__future__` import, a `PendingDeprecationWarning` will be raised.

PEP written by Chris Angelico and Guido van Rossum. Implemented by Chris Angelico, Yury Selivanov and Nick Coghlan.

See also

PEP 479 – Change StopIteration handling inside generators

### PEP 486: Make the Python Launcher aware of virtual environments

PEP 486 makes the Windows launcher (see PEP 397) aware of an active virtual environment. When the default interpreter would be used and the `VIRTUAL_ENV` environment variable is set, the interpreter in the virtual environment will be used.

See also

PEP 486 – Make the Python Launcher aware of virtual environments

### PEP 488: Elimination of PYO files

PEP 488 does away with the concept of `.pyo` files. This means that `.pyc` files represent both unoptimized and optimized bytecode. To prevent the need to constantly regenerate bytecode files, `.pyc` files now have an optional `opt-` tag in their name when the bytecode is optimized. This has the side-effect of no more bytecode file name clashes when running under either `-O` or `-OO`. Consequently, bytecode files generated from `-O`, and `-OO` may now exist simultaneously. `importlib.util.cache_from_source()` has an updated API to help with this change.

See also

PEP 488 – Elimination of PYO files

### PEP 489: Multi-phase extension module initialization

PEP 489 updates extension module initialization to take advantage of the two step module loading mechanism introduced by PEP 451 in Python 3.4.

This change brings the import semantics of extension modules that opt-in to using the new mechanism much closer to those of Python source and bytecode modules, including the ability to use any valid identifier as a module name, rather than being restricted to ASCII.

See also

PEP 488 – Multi-phase extension module initialization

### PEP 485: A function for testing approximate equality

PEP 485 adds the `math.isclose()` and `cmath.isclose()` functions which tell whether two values are approximately equal or “close” to each other. Whether or not two values are considered close is determined according to given absolute and relative tolerances.

See also

PEP 485 – A function for testing approximate equality

## Other Language Changes

Some smaller changes made to the core Python language are:

- Added the `'namereplace'` error handlers. The `'backslashreplace'` error handlers now works with decoding and translating. (Contributed by Serhiy Storchaka in issue 19676 and issue 22286.)
- The -b option now affects comparisons of `bytes` with `int`. (Contributed by Serhiy Storchaka in issue 23681)
- New Kazakh codec `kz1048`. (Contributed by Serhiy Storchaka in issue 22682.)
- Property docstrings are now writable. This is especially useful for `collections.namedtuple()` docstrings. (Contributed by Berker Peksag in issue 24064.)
- New Tajik codec `koi8_t`. (Contributed by Serhiy Storchaka in issue 22681.)

## New Modules

### zipapp

The new `zipapp` module (specified in PEP 441) provides an API and command line tool for creating executable Python Zip Applications, which were introduced in Python 2.6 in issue 1739468 but which were not well publicised, either at the time or since.

With the new module, bundling your application is as simple as putting all the files, including a `__main__.py` file, into a directory `myapp` and running:

    $ python -m zipapp myapp
    $ python myapp.pyz

## Improved Modules

### argparse

- `ArgumentParser` now allows to disable abbreviated usage of long options by setting allow_abbrev to `False`. (Contributed by Jonathan Paugh, Steven Bethard, paul j3 and Daniel Eriksson.)

### cgi

- `FieldStorage` now supports the context management protocol. (Contributed by Berker Peksag in issue 20289.)

### cmath

- `cmath.isclose()` function added. (Contributed by Chris Barker and Tal Einat in issue 24270.)

### code

- The `code.InteractiveInterpreter.showtraceback()` method now prints the full chained traceback, just like the interactive interpreter. (Contributed by Claudiu Popa in issue 17442.)

### collections

- You can now update docstrings produced by `collections.namedtuple()`:

      Point = namedtuple('Point', ['x', 'y'])
      Point.__doc__ = 'ordered pair'
      Point.x.__doc__ = 'abscissa'
      Point.y.__doc__ = 'ordinate'

  (Contributed by Berker Peksag in issue 24064.)

### compileall

- `compileall.compile_dir()` and `compileall`‘s command-line interface can now do parallel bytecode compilation. (Contributed by Claudiu Popa in issue 16104.)

### contextlib

- The new `contextlib.redirect_stderr()` context manager(similar to `contextlib.redirect_stdout()`) makes it easier for utility scripts to handle inflexible APIs that write their output to `sys.stderr` and don’t provide any options to redirect it. (Contributed by Berker Peksag in issue 22389.)

### curses

- The new `curses.update_lines_cols()` function updates the variables `curses.LINES` and `curses.COLS`.

### difflib

- The charset of the HTML document generated by `difflib.HtmlDiff.make_file()` can now be customized by using charset keyword-only parameter. The default charset of HTML document changed from `'ISO-8859-1'` to `'utf-8'`. (Contributed by Berker Peksag in issue 2052.)
- It’s now possible to compare lists of byte strings with `difflib.diff_bytes()` (fixes a regression from Python 2).

### distutils

- The `build` and `build_ext` commands now accept a `-j` option to enable parallel building of extension modules. (Contributed by Antoine Pitrou in issue 5309.)
- Added support for the LZMA compression. (Contributed by Serhiy Storchaka in issue 16314.)

### doctest

- `doctest.DocTestSuite()` returns an empty `unittest.TestSuite` if module contains no docstrings instead of raising `ValueError`. (Contributed by Glenn Jones in issue 15916.)

### email

- A new policy option `mangle_from_` controls whether or not lines that start with “From ” in email bodies are prefixed with a ‘>’ character by generators. The default is `True` for `compat32` and `False` for all other policies. (Contributed by Milan Oberkirch in issue 20098.)
- A new method `get_content_disposition()` provides easy access to a canonical value for the Content-Disposition header (`None` if there is no such header). (Contributed by Abhilash Raj in issue 21083.)
- A new policy option `utf8` can be set `True` to encode email headers using the utf8 charset instead of using encoded words. This allows `Messages` to be formatted according to RFC 6532 and used with an SMTP server that supports the RFC 6531 `SMTPUTF8` extension. (Contributed by R. David Murray in issue 24211.)

### glob

- `iglob()` and `glob()` now support recursive search in subdirectories using the “`**`” pattern. (Contributed by Serhiy Storchaka in issue 13968.)

### idlelib and IDLE

Since idlelib implements the IDLE shell and editor and is not intended for import by other programs, it gets improvements with every release. See `Lib/idlelib/NEWS.txt` for a cumulative list of changes since 3.4.0, as well as changes made in future 3.5.x releases. This file is also available from the IDLE Help -> About Idle dialog.

### imaplib

- `IMAP4` now supports the context management protocol. When used in a `with` statement, the IMAP4 `LOGOUT` command will be called automatically at the end of the block. (Contributed by Tarek Ziadé and Serhiy Storchaka in issue 4972.)
- `imaplib` now supports RFC 5161: the `enable()` extension), and RFC 6855: utf-8 support (internationalized email, via the `UTF8=ACCEPT` argument to `enable()`). A new attribute, `utf8_enabled`, tracks whether or not RFC 6855 support is enabled. Milan Oberkirch, R. David Murray, and Maciej Szulik in issue 21800.)
- `imaplib` now automatically encodes non-ASCII string usernames and passwords using `UTF8`, as recommended by the RFCs. (Contributed by Milan Oberkirch in issue 21800.)

### imghdr

- `what()` now recognizes the OpenEXR format. (Contributed by Martin Vignali and Claudiu Popa in issue 20295.)

### importlib

- `importlib.util.LazyLoader` allows for the lazy loading of modules in applications where startup time is paramount. (Contributed by Brett Cannon in issue 17621.)
- `importlib.abc.InspectLoader.source_to_code()` is now a static method to make it easier to work with source code in a string. With a module object that you want to initialize you can then use `exec(code, module.__dict__)` to execute the code in the module.
- `importlib.util.module_from_spec()` is now the preferred way to create a new module. Compared to `types.ModuleType`, this new function will set the various import-controlled attributes based on the passed-in spec object.

### inspect

- `inspect.Signature` and `inspect.Parameter` are now picklable and hashable. (Contributed by Yury Selivanov in issue 20726 and issue 20334.)
- New method `inspect.BoundArguments.apply_defaults()`. (Contributed by Yury Selivanov in issue 24190.)
- New class method `inspect.Signature.from_callable()`, which makes subclassing of `Signature` easier. (Contributed by Yury Selivanov and Eric Snow in issue 17373.)
- New argument `follow_wrapped` for `inspect.signature()`. (Contributed by Yury Selivanov in issue 20691.)
- New `iscoroutine()`, `iscoroutinefunction()` and `isawaitable()` functions. (Contributed by Yury Selivanov in issue 24017.)
- New `getcoroutinelocals()` and `getcoroutinestate()` functions. (Contributed by Yury Selivanov in issue 24400.)

### ipaddress

- `ipaddress.IPv4Network` and `ipaddress.IPv6Network` now accept an `(address, netmask)` tuple argument, so as to easily construct network objects from existing addresses. (Contributed by Peter Moody and Antoine Pitrou in issue 16531.)

### json

- The output of `json.tool` command line interface is now in the same order as the input. Use the --sort-keys option to sort the output of dictionaries alphabetically by key. (Contributed by Berker Peksag in issue 21650.)
- JSON decoder now raises `json.JSONDecodeError` instead of `ValueError`. (Contributed by Serhiy Storchaka in issue 19361.)

### math

- `math.inf` and `math.nan` constants added. (Contributed by Mark Dickinson in issue 23185.)
- `math.isclose()` function added. (Contributed by Chris Barker and Tal Einat in issue 24270.)

### os

- New `os.scandir()` function that exposes file information from the operating system when listing a directory. `os.scandir()` returns an iterator of `os.DirEntry` objects corresponding to the entries in the directory given by path. (Contributed by Ben Hoyt with the help of Victor Stinner in issue 22524.)
- `os.stat_result` now has a `st_file_attributes` attribute on Windows. (Contributed by Ben Hoyt in issue 21719.)
- `os.urandom()`: On Linux 3.17 and newer, the `getrandom()` syscall is now used when available. On OpenBSD 5.6 and newer, the C `getentropy()` function is now used. These functions avoid the usage of an internal file descriptor.

### os.path

- New `commonpath()` function that extracts common path prefix. Unlike the `commonprefix()` function, it always returns a valid path. (Contributed by Rafik Draoui and Serhiy Storchaka in issue 10395.)

### pickle

- Serializing more “lookupable” objects (such as unbound methods or nested classes) now are supported with pickle protocols < 4. (Contributed by Serhiy Storchaka in issue 23611.)

### poplib

- A new command `utf8()` enables RFC 6856 (internationalized email) support if the POP server supports it. (Contributed by Milan OberKirch in issue 21804.)

### re

- Number of capturing groups in regular expression is no longer limited by 100. (Contributed by Serhiy Storchaka in issue 22437.)
- Now unmatched groups are replaced with empty strings in `re.sub()` and `re.subn()`. (Contributed by Serhiy Storchaka in issue 1519638.)

### shutil

- `move()` now accepts a copy_function argument, allowing, for example, `copy()` to be used instead of the default `copy2()` if there is a need to ignore metadata. (Contributed by Claudiu Popa in issue 19840.)

### signal

- On Windows, `signal.set_wakeup_fd()` now also supports socket handles. (Contributed by Victor Stinner in issue 22018.)
- Different constants of `signal` module are now enumeration values using the `enum` module. This allows meaningful names to be printed during debugging, instead of integer “magic numbers”. (Contributed by Giampaolo Rodola’ in issue 21076.)

### smtpd

- Both `SMTPServer` and `smtpd.SMTPChannel` now accept a decode_data keyword to determine if the DATA portion of the SMTP transaction is decoded using the `utf-8` codec or is instead provided to `process_message()` as a byte string. The default is `True` for backward compatibility reasons, but will change to `False` in Python 3.6. If decode_data is set to `False`, the `process_message()` method must be prepared to accept keyword arguments. (Contributed by Maciej Szulik in issue 19662.)
- `SMTPServer` now advertises the `8BITMIME` extension (RFC 6152) if if decode_data has been set `True`. If the client specifies `BODY=8BITMIME` on the `MAIL` command, it is passed to `process_message()` via the `mail_options` keyword. (Contributed by Milan Oberkirch and R. David Murray in issue 21795.)
- `SMTPServer` now supports the `SMTPUTF8` extension (RFC 6531: Internationalized Email). If the client specified `SMTPUTF8 BODY=8BITMIME` on the `MAIL` command, they are passed to `process_message()` via the `mail_options` keyword. It is the responsibility of the `process_message()` method to correctly handle the `SMTPUTF8` data. (Contributed by Milan Oberkirch in issue 21725.)
- It is now possible to provide, directly or via name resolution, IPv6 addresses in the `SMTPServer` constructor, and have it successfully connect. (Contributed by Milan Oberkirch in issue 14758.)

### smtplib

- A new `auth()` method provides a convenient way to implement custom authentication mechanisms. (Contributed by Milan Oberkirch in issue 15014.)
- Additional debuglevel (2) shows timestamps for debug messages in `smtplib.SMTP`. (Contributed by Gavin Chappell and Maciej Szulik in issue 16914.)
- `smtplib` now supports RFC 6531 (SMTPUTF8) in both the `sendmail()` and `send_message()` commands. (Contributed by Milan Oberkirch and R. David Murray in issue 22027.)

### sndhdr

- `what()` and `whathdr()` now return `namedtuple()`. (Contributed by Claudiu Popa in issue 18615.)

### ssl

- The `do_handshake()`, `read()`, `shutdown()`, and `write()` methods of `ssl.SSLSocket` don’t reset the socket timeout anymore each time bytes are received or sent. The socket timeout is now the maximum total duration of the method.
- Memory BIO Support: new classes `SSLObject`, `MemoryBIO`, and new `SSLContext.wrap_bio` method. (Contributed by Geert Jansen in issue 21965.)

### socket

- New `socket.socket.sendfile()` method allows to send a file over a socket by using high-performance `os.sendfile()` function on UNIX resulting in uploads being from 2x to 3x faster than when using plain `socket.socket.send()`. (Contributed by Giampaolo Rodola’ in issue 17552.)
- The `socket.socket.sendall()` method don’t reset the socket timeout anymore each time bytes are received or sent. The socket timeout is now the maximum total duration to send all data.

### subprocess

- The new `subprocess.run()` function runs subprocesses and returns a `subprocess.CompletedProcess` object. It Provides a more consistent API than `call()`, `check_call()` and `check_output()`.

### sys

- New `set_coroutine_wrapper()` and `get_coroutine_wrapper()` functions. (Contributed by Yury Selivanov in issue 24017.)

### sysconfig

- The user scripts directory on Windows is now versioned. (Contributed by Paul Moore in issue 23437.)

### tarfile

- The `tarfile.open()` function now supports `'x'` (exclusive creation) mode. (Contributed by Berker Peksag in issue 21717.)
- The `extractall()` and `extract()` methods now take a keyword parameter numeric_only. If set to `True`, the extracted files and directories will be owned by the numeric uid and gid from the tarfile. If set to `False` (the default, and the behavior in versions prior to 3.5), they will be owned bythe named user and group in the tarfile. (Contributed by Michael Vogt and Eric Smith in issue 23193.)

### time

- The `time.monotonic()` function is now always available. (Contributed by Victor Stinner in issue 22043.)

### tkinter

- The `tkinter._fix` module used for setting up the Tcl/Tk environment on Windows has been replaced by a private function in the `_tkinter` module which makes no permanent changes to environment variables. (Contributed by Zachary Ware in issue 20035.)

### types

- New `coroutine()` function. (Contributed by Yury Selivanov in issue 24017.)
- New `CoroutineType`. (Contributed by Yury Selivanov in issue 24400.)

### urllib

- A new `HTTPPasswordMgrWithPriorAuth` allows HTTP Basic Authentication credentials to be managed so as to eliminate unnecessary `401` response handling, or to unconditionally send credentials on the first request in order to communicate with servers that return a `404` response instead of a `401` if the `Authorization` header is not sent. (Contributed by Matej Cepl in issue 19494 and Akshit Khurana in issue 7159.)
- A new `urlencode()` parameter quote_via provides a way to control the encoding of query parts if needed. (Contributed by Samwyse and Arnon Yaari in issue 13866.)

### unicodedata

- The `unicodedata` module now uses data from Unicode 8.0.0.

### wsgiref

- headers parameter of `wsgiref.headers.Headers` is now optional. (Contributed by Pablo Torres Navarrete and SilentGhost in issue 5800.)

### xmlrpc

- `xmlrpc.client.ServerProxy` is now a context manager. (Contributed by Claudiu Popa in issue 20627.)

### xml.sax

- SAX parsers now support a character stream of `InputSource` object. (Contributed by Serhiy Storchaka in issue 2175.)

### faulthandler

- `enable()`, `register()`, `dump_traceback()` and `dump_traceback_later()` functions now accept file descriptors. (Contributed by Wei Wu in issue 23566.)

### zipfile

- Added support for writing ZIP files to unseekable streams. (Contributed by Serhiy Storchaka in issue 23252.)
- The `zipfile.ZipFile.open()` function now supports `'x'` (exclusive creation) mode. (Contributed by Serhiy Storchaka in issue 21717.)

## Optimizations

The following performance enhancements have been added:

- `os.walk()` has been sped up by 3-5x on POSIX systems and 7-20x on Windows. This was done using the new `os.scandir()` function, which exposes file information from the underlying `readdir` and `FindFirstFile`/`FindNextFile` system calls. (Contributed by Ben Hoyt with help from Victor Stinner in issue 23605.)
- Construction of `bytes(int)` (filled by zero bytes) is faster and uses less memory for large objects. `calloc()` is used instead of `malloc()` to allocate memory for these objects.
- Some operations on `IPv4Network` and `IPv6Network` have been massively sped up, such as `subnets()`, `supernet()`, `summarize_address_range()`, `collapse_addresses()`. The speed up can range from 3x to 15x. (issue 21486, issue 21487, issue 20826)
- Many operations on `io.BytesIO` are now 50% to 100% faster. (Contributed by Serhiy Storchaka in issue 15381 and David Wilson in issue 22003.)
- `marshal.dumps()` is now faster (65%-85% with versions 3–4, 20-25% with versions 0–2 on typical data, and up to 5x in best cases). (Contributed by Serhiy Storchaka in issue 20416 and issue 23344.)
- The UTF-32 encoder is now 3x to 7x faster. (Contributed by Serhiy Storchaka in issue 15027.)

## Build and C API Changes

Changes to Python’s build process and to the C API include:

- New `calloc` functions:
  - `PyMem_RawCalloc()`
  - `PyMem_Calloc()`
  - `PyObject_Calloc()`
  - `_PyObject_GC_Calloc()`
- Windows builds now require Microsoft Visual C++ 14.0, which is available as part of Visual Studio 2015.

## Deprecated

### New Keywords

`async` and `await` are not recommended to be used as variable, class, function or module names. Introduced by PEP 492 in Python 3.5, they will become proper keywords in Python 3.7.

### Unsupported Operating Systems

- Windows XP - Per PEP 11, Microsoft support of Windows XP has ended.

### Deprecated Python modules, functions and methods

- The `formatter` module has now graduated to full deprecation and is still slated for removal in Python 3.6.
- `smtpd` has in the past always decoded the DATA portion of email messages using the `utf-8` codec. This can now be controlled by the new decode_data keyword to `SMTPServer`. The default value is `True`, but this default is deprecated. Specify the decode_data keyword with an appropriate value to avoid the deprecation warning.
- Directly assigning values to the `key`, `value` and `coded_value` of `Morsel` objects is deprecated. Use the `set()` method instead. In addition, the undocumented LegalChars parameter of `set()` is deprecated, and is now ignored.
- Passing a format string as keyword argument format_string to the `format()` method of the `string.Formatter` class has been deprecated.
- `platform.dist()` and `platform.linux_distribution()` functions are now deprecated and will be removed in Python 3.7. Linux distributions use too many different ways of describing themselves, so the functionality is left to a package. (Contributed by Vajrasky Kok and Berker Peksag in issue 1322.)
- The previously undocumented `from_function` and `from_builtin` methods of `inspect.Signature` are deprecated. Use new `inspect.Signature.from_callable()` instead. (Contributed by Yury Selivanov in issue 24248.)
- `inspect.getargspec()` is deprecated and scheduled to be removed in Python 3.6. (See issue 20438 for details.)
- `getfullargspec()`, `getargvalues()`, `getcallargs()`, `getargvalues()`, `formatargspec()`, and `formatargvalues()` are deprecated in favor of `inspect.signature()` API. (See issue 20438 for details.)

### Deprecated functions and types of the C API

- None yet.

### Deprecated features

- None yet.

## Removed

### API and Feature Removals

The following obsolete and previously deprecated APIs and features have been removed:

- The `__version__` attribute has been dropped from the email package. The email code hasn’t been shipped separately from the stdlib for a long time, and the `__version__` string was not updated in the last few releases.
- The internal `Netrc` class in the `ftplib` module was deprecated in 3.4, and has now been removed. (Contributed by Matt Chaput in issue 6623.)
- The concept of `.pyo` files has been removed.
- The JoinableQueue class in the provisional asyncio module was deprecated in 3.4.4 and is now removed (issue 23464).

## Porting to Python 3.5

This section lists previously described changes and other bugfixes that may require changes to your code.

### Changes in the Python API

- PEP 475: System calls are now retried when interrupted by a signal instead of raising `InterruptedError` if the Python signal handler does not raise an exception.
- Before Python 3.5, a `datetime.time` object was considered to be false if it represented midnight in UTC. This behavior was considered obscure and error-prone and has been removed in Python 3.5. See issue 13936 for full details.
- `ssl.SSLSocket.send()` now raises either `ssl.SSLWantReadError` or `ssl.SSLWantWriteError` on a non-blocking socket if the operation would block. Previously, it would return 0. See issue 20951.
- The `__name__` attribute of generator is now set from the function name, instead of being set from the code name. Use `gen.gi_code.co_name` to retrieve the code name. Generators also have a new `__qualname__` attribute, the qualified name, which is now used for the representation of a generator (`repr(gen)`). See issue 21205.
- The deprecated “strict” mode and argument of `HTMLParser`, `HTMLParser.error()`, and the `HTMLParserError` exception have been removed. (Contributed by Ezio Melotti in issue 15114.) The convert_charrefs argument of `HTMLParser` is now `True` by default. (Contributed by Berker Peksag in issue 21047.)
- Although it is not formally part of the API, it is worth noting for porting purposes (ie: fixing tests) that error messages that were previously of the form “‘sometype’ does not support the buffer protocol” are now of the form “a bytes-like object is required, not ‘sometype’”. (Contributed by Ezio Melotti in issue 16518.)
- If the current directory is set to a directory that no longer exists then `FileNotFoundError` will no longer be raised and instead `find_spec()` will return `None` without caching `None` in `sys.path_importer_cache` which is different than the typical case (issue 22834).
- HTTP status code and messages from `http.client` and `http.server` were refactored into a common `HTTPStatus` enum. The values in `http.client` and `http.server` remain available for backwards compatibility. (Contributed by Demian Brecht in issue 21793.)
- When an import loader defines `exec_module()` it is now expected to also define `create_module()` (raises a `DeprecationWarning` now, will be an error in Python 3.6). If the loader inherits from `importlib.abc.Loader` then there is nothing to do, else simply define `create_module()` to return `None` (issue 23014).
- `re.split()` always ignored empty pattern matches, so the `'x*'` pattern worked the same as `'x+'`, and the `'\b'` pattern never worked. Now `re.split()` raises a warning if the pattern could match an empty string. For compatibility use patterns that never match an empty string (e.g. `'x+'` instead of `'x*'`). Patterns that could only match an empty string (such as `'\b'`) now raise an error.
- The `Morsel` dict-like interface has been made self consistent: morsel comparison now takes the `key` and `value` into account, `copy()` now results in a `Morsel` instance rather than a `dict`, and `update()` will now raise an exception if any of the keys in the update dictionary are invalid. In addition, the undocumented LegalChars parameter of `set()` is deprecated and is now ignored. (issue 2211)
- PEP 488 has removed `.pyo` files from Python and introduced the optional `opt-` tag in `.pyc` file names. The `importlib.util.cache_from_source()` has gained an optimization parameter to help control the `opt-` tag. Because of this, the debug_override parameter of the function is now deprecated. .pyo files are also no longer supported as a file argument to the Python interpreter and thus serve no purpose when distributed on their own (i.e. sourcless code distribution). Due to the fact that the magic number for bytecode has changed in Python 3.5, all old .pyo files from previous versions of Python are invalid regardless of this PEP.
- The `socket` module now exports the CAN_RAW_FD_FRAMES constant on linux 3.6 and greater.
- The `pygettext.py` Tool now uses the standard +NNNN format for timezones in the POT-Creation-Date header.
- The `smtplib` module now uses `sys.stderr` instead of previous module level `stderr` variable for debug output. If your (test) program depends on patching the module level variable to capture the debug output, you will need to update it to capture sys.stderr instead.
- The `str.startswith()` and `str.endswith()` methods no longer return `True` when finding the empty string and the indexes are completely out of range. See issue 24284.
- The `inspect.getdoc()` function now returns documentation strings inherited from base classes. Documentation strings no longer need to be duplicated if the inherited documentation is appropriate. To suppress an inherited string, an empty string must be specified (or the documentation may be filled in). This change affects the output of the `pydoc` module and the `help()` function. See issue 15582.

### Changes in the C API

- The undocumented `format` member of the (non-public) `PyMemoryViewObject` structure has been removed.

  All extensions relying on the relevant parts in `memoryobject.h` must be rebuilt.

- The `PyMemAllocator` structure was renamed to `PyMemAllocatorEx` and a new `calloc` field was added.

- Removed non-documented macro `PyObject_REPR` which leaked references. Use format character `%R` in `PyUnicode_FromFormat()`-like functions to format the `repr()` of the object.

- Because the lack of the `__module__` attribute breaks pickling and introspection, a deprecation warning now is raised for builtin type without the `__module__` attribute. Would be an AttributeError in future. (issue 20204)

- As part of PEP 492 implementation, `tp_reserved` slot of `PyTypeObject` was replaced with a `tp_as_async` slot. Refer to Coroutine Objects for new types, structures and functions.

### Navigation

- index
- modules |
- next |
- previous |
- Python »
- 3.6.0a0 Documentation »
- What’s New in Python »