3.5.txt

----

The "Enum" callable has a new parameter *start* to specify the initial
number of enum values if only *names* are provided:

   >>> Animal = enum.Enum('Animal', 'cat dog', start=10)
   >>> Animal.cat
   <Animal.cat: 10>
   >>> Animal.dog
   <Animal.dog: 11>

(Contributed by Ethan Furman in bpo-21706.)


faulthandler
------------

The "enable()", "register()", "dump_traceback()" and
"dump_traceback_later()" functions now accept file descriptors in
addition to file-like objects. (Contributed by Wei Wu in bpo-23566.)


functools
---------

Most of the "lru_cache()" machinery is now implemented in C, making it
significantly faster.  (Contributed by Matt Joiner, Alexey Kachayev,
and Serhiy Storchaka in bpo-14373.)


glob
----

The "iglob()" and "glob()" functions now support recursive search in
subdirectories, using the ""**"" pattern. (Contributed by Serhiy
Storchaka in bpo-13968.)


gzip
----

The *mode* argument of the "GzipFile" constructor now accepts ""x"" to
request exclusive creation. (Contributed by Tim Heaney in bpo-19222.)


heapq
-----

Element comparison in "merge()" can now be customized by passing a
*key function* in a new optional *key* keyword argument, and a new
optional *reverse* keyword argument can be used to reverse element
comparison:

   >>> import heapq
   >>> a = ['9', '777', '55555']
   >>> b = ['88', '6666']
   >>> list(heapq.merge(a, b, key=len))
   ['9', '88', '777', '6666', '55555']
   >>> list(heapq.merge(reversed(a), reversed(b), key=len, reverse=True))
   ['55555', '6666', '777', '88', '9']

(Contributed by Raymond Hettinger in bpo-13742.)


http
----

A new "HTTPStatus" enum that defines a set of HTTP status codes,
reason phrases and long descriptions written in English. (Contributed
by Demian Brecht in bpo-21793.)


http.client
-----------

"HTTPConnection.getresponse()" now raises a "RemoteDisconnected"
exception when a remote server connection is closed unexpectedly.
Additionally, if a "ConnectionError" (of which "RemoteDisconnected" is
a subclass) is raised, the client socket is now closed automatically,
and will reconnect on the next request:

   import http.client
   conn = http.client.HTTPConnection('www.python.org')
   for retries in range(3):
       try:
           conn.request('GET', '/')
           resp = conn.getresponse()
       except http.client.RemoteDisconnected:
           pass

(Contributed by Martin Panter in bpo-3566.)


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
-------

The "IMAP4" class now supports the *context manager* 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 bpo-4972.)

The "imaplib" module now supports **RFC 5161** (ENABLE Extension) and
**RFC 6855** (UTF-8 Support) via the "IMAP4.enable()" method.  A new
"IMAP4.utf8_enabled" attribute tracks whether or not **RFC 6855**
support is enabled. (Contributed by Milan Oberkirch, R. David Murray,
and Maciej Szulik in bpo-21800.)

The "imaplib" module now automatically encodes non-ASCII string
usernames and passwords using UTF-8, as recommended by the RFCs.
(Contributed by Milan Oberkirch in bpo-21800.)


imghdr
------

The "what()" function now recognizes the OpenEXR format (contributed
by Martin Vignali and Claudiu Popa in bpo-20295), and the WebP format
(contributed by Fabrice Aneche and Claudiu Popa in bpo-20197.)


importlib
---------

The "util.LazyLoader" class allows for lazy loading of modules in
applications where startup time is important. (Contributed by Brett
Cannon in bpo-17621.)

The "abc.InspectLoader.source_to_code()" method is now a static
method.  This makes it easier to initialize a module object with code
compiled from a string by running "exec(code, module.__dict__)".
(Contributed by Brett Cannon in bpo-21156.)

The new "util.module_from_spec()" function is now the preferred way to
create a new module.  As opposed to creating a "types.ModuleType"
instance directly, this new function will set the various import-
controlled attributes based on the passed-in spec object.
(Contributed by Brett Cannon in bpo-20383.)


inspect
-------

Both the "Signature" and "Parameter" classes are now picklable and
hashable.  (Contributed by Yury Selivanov in bpo-20726 and bpo-20334.)

A new "BoundArguments.apply_defaults()" method provides a way to set
default values for missing arguments:

   >>> def foo(a, b='ham', *args): pass
   >>> ba = inspect.signature(foo).bind('spam')
   >>> ba.apply_defaults()
   >>> ba.arguments
   OrderedDict([('a', 'spam'), ('b', 'ham'), ('args', ())])

(Contributed by Yury Selivanov in bpo-24190.)

A new class method "Signature.from_callable()" makes subclassing of
"Signature" easier.  (Contributed by Yury Selivanov and Eric Snow in
bpo-17373.)

The "signature()" function now accepts a *follow_wrapped* optional
keyword argument, which, when set to "False", disables automatic
following of "__wrapped__" links. (Contributed by Yury Selivanov in
bpo-20691.)

A set of new functions to inspect *coroutine functions* and *coroutine
objects* has been added: "iscoroutine()", "iscoroutinefunction()",
"isawaitable()", "getcoroutinelocals()", and "getcoroutinestate()".
(Contributed by Yury Selivanov in bpo-24017 and bpo-24400.)

The "stack()", "trace()", "getouterframes()", and "getinnerframes()"
functions now return a list of named tuples. (Contributed by Daniel
Shahaf in bpo-16808.)


io
--

A new "BufferedIOBase.readinto1()" method, that uses at most one call
to the underlying raw stream's "RawIOBase.read()" or
"RawIOBase.readinto()" methods. (Contributed by Nikolaus Rath in
bpo-20578.)


ipaddress
---------

Both the "IPv4Network" and "IPv6Network" classes now accept an
"(address, netmask)" tuple argument, so as to easily construct network
objects from existing addresses:

   >>> import ipaddress
   >>> ipaddress.IPv4Network(('127.0.0.0', 8))
   IPv4Network('127.0.0.0/8')
   >>> ipaddress.IPv4Network(('127.0.0.0', '255.0.0.0'))
   IPv4Network('127.0.0.0/8')

(Contributed by Peter Moody and Antoine Pitrou in bpo-16531.)

A new "reverse_pointer" attribute for the "IPv4Network" and
"IPv6Network" classes returns the name of the reverse DNS PTR record:

   >>> import ipaddress
   >>> addr = ipaddress.IPv4Address('127.0.0.1')
   >>> addr.reverse_pointer
   '1.0.0.127.in-addr.arpa'
   >>> addr6 = ipaddress.IPv6Address('::1')
   >>> addr6.reverse_pointer
   '1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa'

(Contributed by Leon Weber in bpo-20480.)


json
----

The "json.tool" command line interface now preserves the order of keys
in JSON objects passed in input.  The new "--sort-keys" option can be
used to sort the keys alphabetically. (Contributed by Berker Peksag in
bpo-21650.)

JSON decoder now raises "JSONDecodeError" instead of "ValueError" to
provide better context information about the error. (Contributed by
Serhiy Storchaka in bpo-19361.)


linecache
---------

A new "lazycache()" function can be used to capture information about
a non-file-based module to permit getting its lines later via
"getline()". This avoids doing I/O until a line is actually needed,
without having to carry the module globals around indefinitely.
(Contributed by Robert Collins in bpo-17911.)


locale
------

A new "delocalize()" function can be used to convert a string into a
normalized number string, taking the "LC_NUMERIC" settings into
account:

   >>> import locale
   >>> locale.setlocale(locale.LC_NUMERIC, 'de_DE.UTF-8')
   'de_DE.UTF-8'
   >>> locale.delocalize('1.234,56')
   '1234.56'
   >>> locale.setlocale(locale.LC_NUMERIC, 'en_US.UTF-8')
   'en_US.UTF-8'
   >>> locale.delocalize('1,234.56')
   '1234.56'

(Contributed by Cédric Krier in bpo-13918.)


logging
-------

All logging methods ("Logger" "log()", "exception()", "critical()",
"debug()", etc.), now accept exception instances as an *exc_info*
argument, in addition to boolean values and exception tuples:

   >>> import logging
   >>> try:
   ...     1/0
   ... except ZeroDivisionError as ex:
   ...     logging.error('exception', exc_info=ex)
   ERROR:root:exception

(Contributed by Yury Selivanov in bpo-20537.)

The "handlers.HTTPHandler" class now accepts an optional
"ssl.SSLContext" instance to configure SSL settings used in an HTTP
connection. (Contributed by Alex Gaynor in bpo-22788.)

The "handlers.QueueListener" class now takes a *respect_handler_level*
keyword argument which, if set to "True", will pass messages to
handlers taking handler levels into account. (Contributed by Vinay
Sajip.)


lzma
----

The "LZMADecompressor.decompress()" method now accepts an optional
*max_length* argument to limit the maximum size of decompressed data.
(Contributed by Martin Panter in bpo-15955.)


math
----

Two new constants have been added to the "math" module: "inf" and
"nan".  (Contributed by Mark Dickinson in bpo-23185.)

A new function "isclose()" provides a way to test for approximate
equality. (Contributed by Chris Barker and Tal Einat in bpo-24270.)

A new "gcd()" function has been added.  The "fractions.gcd()" function
is now deprecated. (Contributed by Mark Dickinson and Serhiy Storchaka
in bpo-22486.)


multiprocessing
---------------

"sharedctypes.synchronized()" objects now support the *context
manager* protocol. (Contributed by Charles-François Natali in
bpo-21565.)


operator
--------

"attrgetter()", "itemgetter()", and "methodcaller()" objects now
support pickling. (Contributed by Josh Rosenberg and Serhiy Storchaka
in bpo-22955.)

New "matmul()" and "imatmul()" functions to perform matrix
multiplication. (Contributed by Benjamin Peterson in bpo-21176.)


os
--

The new "scandir()" function returning an iterator of "DirEntry"
objects has been added.  If possible, "scandir()" extracts file
attributes while scanning a directory, removing the need to perform
subsequent system calls to determine file type or attributes, which
may significantly improve performance.  (Contributed by Ben Hoyt with
the help of Victor Stinner in bpo-22524.)

On Windows, a new "stat_result.st_file_attributes" attribute is now
available.  It corresponds to the "dwFileAttributes" member of the
"BY_HANDLE_FILE_INFORMATION" structure returned by
"GetFileInformationByHandle()".  (Contributed by Ben Hoyt in
bpo-21719.)

The "urandom()" function now uses the "getrandom()" syscall on Linux
3.17 or newer, and "getentropy()" on OpenBSD 5.6 and newer, removing
the need to use "/dev/urandom" and avoiding failures due to potential
file descriptor exhaustion.  (Contributed by Victor Stinner in
bpo-22181.)

New "get_blocking()" and "set_blocking()" functions allow getting and
setting a file descriptor's blocking mode ("O_NONBLOCK".) (Contributed
by Victor Stinner in bpo-22054.)

The "truncate()" and "ftruncate()" functions are now supported on
Windows.  (Contributed by Steve Dower in bpo-23668.)

There is a new "os.path.commonpath()" function returning the longest
common sub-path of each passed pathname.  Unlike the
"os.path.commonprefix()" function, it always returns a valid path:

   >>> os.path.commonprefix(['/usr/lib', '/usr/local/lib'])
   '/usr/l'

   >>> os.path.commonpath(['/usr/lib', '/usr/local/lib'])
   '/usr'

(Contributed by Rafik Draoui and Serhiy Storchaka in bpo-10395.)


pathlib
-------

The new "Path.samefile()" method can be used to check whether the path
points to the same file as another path, which can be either another
"Path" object, or a string:

   >>> import pathlib
   >>> p1 = pathlib.Path('/etc/hosts')
   >>> p2 = pathlib.Path('/etc/../etc/hosts')
   >>> p1.samefile(p2)
   True

(Contributed by Vajrasky Kok and Antoine Pitrou in bpo-19775.)

The "Path.mkdir()" method now accepts a new optional *exist_ok*
argument to match "mkdir -p" and "os.makedirs()" functionality.
(Contributed by Berker Peksag in bpo-21539.)

There is a new "Path.expanduser()" method to expand "~" and "~user"
prefixes.  (Contributed by Serhiy Storchaka and Claudiu Popa in
bpo-19776.)

A new "Path.home()" class method can be used to get a "Path" instance
representing the user’s home directory. (Contributed by Victor Salgado
and Mayank Tripathi in bpo-19777.)

New "Path.write_text()", "Path.read_text()", "Path.write_bytes()",
"Path.read_bytes()" methods to simplify read/write operations on
files.

The following code snippet will create or rewrite existing file
"~/spam42":

   >>> import pathlib
   >>> p = pathlib.Path('~/spam42')
   >>> p.expanduser().write_text('ham')
   3

(Contributed by Christopher Welborn in bpo-20218.)


pickle
------

Nested objects, such as unbound methods or nested classes, can now be
pickled using pickle protocols older than protocol version 4. Protocol
version 4 already supports these cases.  (Contributed by Serhiy
Storchaka in bpo-23611.)


poplib
------

A new "POP3.utf8()" command enables **RFC 6856** (Internationalized
Email) support, if a POP server supports it. (Contributed by Milan
OberKirch in bpo-21804.)


re
--

References and conditional references to groups with fixed length are
now allowed in lookbehind assertions:

   >>> import re
   >>> pat = re.compile(r'(a|b).(?<=\1)c')
   >>> pat.match('aac')
   <_sre.SRE_Match object; span=(0, 3), match='aac'>
   >>> pat.match('bbc')
   <_sre.SRE_Match object; span=(0, 3), match='bbc'>

(Contributed by Serhiy Storchaka in bpo-9179.)

The number of capturing groups in regular expressions is no longer
limited to 100.  (Contributed by Serhiy Storchaka in bpo-22437.)

The "sub()" and "subn()" functions now replace unmatched groups with
empty strings instead of raising an exception. (Contributed by Serhiy
Storchaka in bpo-1519638.)

The "re.error" exceptions have new attributes, "msg", "pattern",
"pos", "lineno", and "colno", that provide better context information
about the error:

   >>> re.compile("""
   ...     (?x)
   ...     .++
   ... """)
   Traceback (most recent call last):
      ...
   sre_constants.error: multiple repeat at position 16 (line 3, column 7)

(Contributed by Serhiy Storchaka in bpo-22578.)


readline
--------

A new "append_history_file()" function can be used to append the
specified number of trailing elements in history to the given file.
(Contributed by Bruno Cauet in bpo-22940.)


selectors
---------

The new "DevpollSelector" supports efficient "/dev/poll" polling on
Solaris. (Contributed by Giampaolo Rodola' in bpo-18931.)


shutil
------

The "move()" function now accepts a *copy_function* argument,
allowing, for example, the "copy()" function to be used instead of the
default "copy2()" if there is a need to ignore file metadata when
moving. (Contributed by Claudiu Popa in bpo-19840.)

The "make_archive()" function now supports the *xztar* format.
(Contributed by Serhiy Storchaka in bpo-5411.)


signal
------

On Windows, the "set_wakeup_fd()" function now also supports socket
handles.  (Contributed by Victor Stinner in bpo-22018.)

Various "SIG*" constants in the "signal" module have been converted
into "Enums".  This allows meaningful names to be printed during
debugging, instead of integer "magic numbers". (Contributed by
Giampaolo Rodola' in bpo-21076.)


smtpd
-----

Both the "SMTPServer" and "SMTPChannel" classes now accept a
*decode_data* keyword argument to determine if the "DATA" portion of
the SMTP transaction is decoded using the ""utf-8"" codec or is
instead provided to the "SMTPServer.process_message()" method 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 bpo-19662.)

The "SMTPServer" class now advertises the "8BITMIME" extension (**RFC
6152**) if *decode_data* has been set "True".  If the client specifies
"BODY=8BITMIME" on the "MAIL" command, it is passed to
"SMTPServer.process_message()" via the *mail_options* keyword.
(Contributed by Milan Oberkirch and R.  David Murray in bpo-21795.)

The "SMTPServer" class now also supports the "SMTPUTF8" extension
(**RFC 6531**: Internationalized Email).  If the client specified
"SMTPUTF8 BODY=8BITMIME" on the "MAIL" command, they are passed to
"SMTPServer.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 bpo-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 bpo-14758.)


smtplib
-------

A new "SMTP.auth()" method provides a convenient way to implement
custom authentication mechanisms. (Contributed by Milan Oberkirch in
bpo-15014.)

The "SMTP.set_debuglevel()" method now accepts an additional
debuglevel (2), which enables timestamps in debug messages.
(Contributed by Gavin Chappell and Maciej Szulik in bpo-16914.)

Both the "SMTP.sendmail()" and "SMTP.send_message()" methods now
support **RFC 6531** (SMTPUTF8). (Contributed by Milan Oberkirch and
R. David Murray in bpo-22027.)


sndhdr
------

The "what()" and "whathdr()" functions  now return a "namedtuple()".
(Contributed by Claudiu Popa in bpo-18615.)


socket
------

Functions with timeouts now use a monotonic clock, instead of a system
clock. (Contributed by Victor Stinner in bpo-22043.)

A new "socket.sendfile()" method allows sending a file over a socket
by using the high-performance "os.sendfile()" function on UNIX,
resulting in uploads being from 2 to 3 times faster than when using
plain "socket.send()". (Contributed by Giampaolo Rodola' in
bpo-17552.)

The "socket.sendall()" method no longer resets the socket timeout
every time bytes are received or sent.  The socket timeout is now the
maximum total duration to send all data. (Contributed by Victor
Stinner in bpo-23853.)

The *backlog* argument of the "socket.listen()" method is now
optional.  By default it is set to "SOMAXCONN" or to "128", whichever
is less. (Contributed by Charles-François Natali in bpo-21455.)


ssl
---


Memory BIO Support
~~~~~~~~~~~~~~~~~~

(Contributed by Geert Jansen in bpo-21965.)

The new "SSLObject" class has been added to provide SSL protocol
support for cases when the network I/O capabilities of "SSLSocket" are
not necessary or are suboptimal.  "SSLObject" represents an SSL
protocol instance, but does not implement any network I/O methods, and
instead provides a memory buffer interface.  The new "MemoryBIO" class
can be used to pass data between Python and an SSL protocol instance.

The memory BIO SSL support is primarily intended to be used in
frameworks implementing asynchronous I/O for which "SSLSocket"'s
readiness model ("select/poll") is inefficient.

A new "SSLContext.wrap_bio()" method can be used to create a new
"SSLObject" instance.


Application-Layer Protocol Negotiation Support
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

(Contributed by Benjamin Peterson in bpo-20188.)

Where OpenSSL support is present, the "ssl" module now implements the
*Application-Layer Protocol Negotiation* TLS extension as described in
**RFC 7301**.

The new "SSLContext.set_alpn_protocols()" can be used to specify which
protocols a socket should advertise during the TLS handshake.

The new "SSLSocket.selected_alpn_protocol()" returns the protocol that
was selected during the TLS handshake. The "HAS_ALPN" flag indicates
whether ALPN support is present.


Other Changes
~~~~~~~~~~~~~

There is a new "SSLSocket.version()" method to query the actual
protocol version in use. (Contributed by Antoine Pitrou in bpo-20421.)

The "SSLSocket" class now implements a "SSLSocket.sendfile()" method.
(Contributed by Giampaolo Rodola' in bpo-17552.)

The "SSLSocket.send()" method now raises either the
"ssl.SSLWantReadError" or "ssl.SSLWantWriteError" exception on a non-
blocking socket if the operation would block. Previously, it would
return "0".  (Contributed by Nikolaus Rath in bpo-20951.)

The "cert_time_to_seconds()" function now interprets the input time as
UTC and not as local time, per **RFC 5280**.  Additionally, the return
value is always an "int". (Contributed by Akira Li in bpo-19940.)

New "SSLObject.shared_ciphers()" and "SSLSocket.shared_ciphers()"
methods return the list of ciphers sent by the client during the
handshake. (Contributed by Benjamin Peterson in bpo-23186.)

The "SSLSocket.do_handshake()", "SSLSocket.read()",
"SSLSocket.shutdown()", and "SSLSocket.write()" methods of the
"SSLSocket" class no longer reset the socket timeout every time bytes
are received or sent. The socket timeout is now the maximum total
duration of the method. (Contributed by Victor Stinner in bpo-23853.)

The "match_hostname()" function now supports matching of IP addresses.
(Contributed by Antoine Pitrou in bpo-23239.)


sqlite3
-------

The "Row" class now fully supports the sequence protocol, in
particular "reversed()" iteration and slice indexing. (Contributed by
Claudiu Popa in bpo-10203; by Lucas Sinclair, Jessica McKellar, and
Serhiy Storchaka in bpo-13583.)


subprocess
----------

The new "run()" function has been added. It runs the specified command
and returns a "CompletedProcess" object, which describes a finished
process.  The new API is more consistent and is the recommended
approach to invoking subprocesses in Python code that does not need to
maintain compatibility with earlier Python versions. (Contributed by
Thomas Kluyver in bpo-23342.)

Examples:

   >>> subprocess.run(["ls", "-l"])  # doesn't capture output
   CompletedProcess(args=['ls', '-l'], returncode=0)

   >>> subprocess.run("exit 1", shell=True, check=True)
   Traceback (most recent call last):
     ...
   subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1

   >>> subprocess.run(["ls", "-l", "/dev/null"], stdout=subprocess.PIPE)
   CompletedProcess(args=['ls', '-l', '/dev/null'], returncode=0,
   stdout=b'crw-rw-rw- 1 root root 1, 3 Jan 23 16:23 /dev/null\n')


sys
---

A new "set_coroutine_wrapper()" function allows setting a global hook
that will be called whenever a *coroutine object* is created by an
"async def" function.  A corresponding "get_coroutine_wrapper()" can
be used to obtain a currently set wrapper.  Both functions are
*provisional*, and are intended for debugging purposes only.
(Contributed by Yury Selivanov in bpo-24017.)

A new "is_finalizing()" function can be used to check if the Python
interpreter is *shutting down*. (Contributed by Antoine Pitrou in
bpo-22696.)


sysconfig
---------

The name of the user scripts directory on Windows now includes the
first two components of the Python version. (Contributed by Paul Moore
in bpo-23437.)


tarfile
-------

The *mode* argument of the "open()" function now accepts ""x"" to
request exclusive creation.  (Contributed by Berker Peksag in
bpo-21717.)

The "TarFile.extractall()" and "TarFile.extract()" methods now take a
keyword argument *numeric_owner*.  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 by the named user and group
in the tarfile. (Contributed by Michael Vogt and Eric Smith in
bpo-23193.)

The "TarFile.list()" now accepts an optional *members* keyword
argument that can be set to a subset of the list returned by
"TarFile.getmembers()". (Contributed by Serhiy Storchaka in
bpo-21549.)


threading
---------

Both the "Lock.acquire()" and "RLock.acquire()" methods now use a
monotonic clock for timeout management. (Contributed by Victor Stinner
in bpo-22043.)


time
----

The "monotonic()" function is now always available. (Contributed by
Victor Stinner in bpo-22043.)


timeit
------

A new command line option "-u" or "--unit=*U*" can be used to specify
the time unit for the timer output.  Supported options are "usec",
"msec", or "sec".  (Contributed by Julian Gindi in bpo-18983.)

The "timeit()" function has a new *globals* parameter for specifying
the namespace in which the code will be running. (Contributed by Ben
Roberts in bpo-2527.)


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 bpo-20035.)


traceback
---------

New "walk_stack()" and "walk_tb()" functions to conveniently traverse
frame and traceback objects. (Contributed by Robert Collins in
bpo-17911.)

New lightweight classes: "TracebackException", "StackSummary", and
"FrameSummary". (Contributed by Robert Collins in bpo-17911.)

Both the "print_tb()" and "print_stack()" functions now support
negative values for the *limit* argument. (Contributed by Dmitry
Kazakov in bpo-22619.)


types
-----

A new "coroutine()" function to transform *generator* and "generator-
like" objects into *awaitables*. (Contributed by Yury Selivanov in
bpo-24017.)

A new type called "CoroutineType", which is used for *coroutine*
objects created by "async def" functions. (Contributed by Yury
Selivanov in bpo-24400.)


unicodedata
-----------

The "unicodedata" module now uses data from Unicode 8.0.0.


unittest
--------

The "TestLoader.loadTestsFromModule()" method now accepts a keyword-
only argument *pattern* which is passed to "load_tests" as the third
argument.  Found packages are now checked for "load_tests" regardless
of whether their path matches *pattern*, because it is impossible for
a package name to match the default pattern. (Contributed by Robert
Collins and Barry A. Warsaw in bpo-16662.)

Unittest discovery errors now are exposed in the "TestLoader.errors"
attribute of the "TestLoader" instance. (Contributed by Robert Collins
in bpo-19746.)

A new command line option "--locals" to show local variables in
tracebacks.  (Contributed by Robert Collins in bpo-22936.)


unittest.mock
-------------

The "Mock" class has the following improvements:

* The class constructor has a new *unsafe* parameter, which causes
  mock objects to raise "AttributeError" on attribute names starting
  with ""assert"". (Contributed by Kushal Das in bpo-21238.)

* A new "Mock.assert_not_called()" method to check if the mock object
  was called. (Contributed by Kushal Das in bpo-21262.)

The "MagicMock" class now supports "__truediv__()", "__divmod__()" and
"__matmul__()" operators. (Contributed by Johannes Baiter in
bpo-20968, and Håkan Lövdahl in bpo-23581 and bpo-23568.)

It is no longer necessary to explicitly pass "create=True" to the
"patch()" function when patching builtin names. (Contributed by Kushal
Das in bpo-17660.)


urllib
------

A new "request.HTTPPasswordMgrWithPriorAuth" class 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 bpo-19494 and Akshit
Khurana in bpo-7159.)

A new *quote_via* argument for the "parse.urlencode()" function
provides a way to control the encoding of query parts if needed.
(Contributed by Samwyse and Arnon Yaari in bpo-13866.)

The "request.urlopen()" function accepts an "ssl.SSLContext" object as
a *context* argument, which will be used for the HTTPS connection.
(Contributed by Alex Gaynor in bpo-22366.)

The "parse.urljoin()" was updated to use the **RFC 3986** semantics
for the resolution of relative URLs, rather than **RFC 1808** and
**RFC 2396**. (Contributed by Demian Brecht and Senthil Kumaran in
bpo-22118.)


wsgiref
-------

The *headers* argument of the "headers.Headers" class constructor is
now optional. (Contributed by Pablo Torres Navarrete and SilentGhost
in bpo-5800.)


xmlrpc
------

The "client.ServerProxy" class now supports the *context manager*
protocol. (Contributed by Claudiu Popa in bpo-20627.)

The "client.ServerProxy" constructor now accepts an optional
"ssl.SSLContext" instance. (Contributed by Alex Gaynor in bpo-22960.)


xml.sax
-------

SAX parsers now support a character stream of the
"xmlreader.InputSource" object. (Contributed by Serhiy Storchaka in
bpo-2175.)

"parseString()" now accepts a "str" instance. (Contributed by Serhiy
Storchaka in bpo-10590.)


zipfile
-------

ZIP output can now be written to unseekable streams. (Contributed by
Serhiy Storchaka in bpo-23252.)

The *mode* argument of "ZipFile.open()" method now accepts ""x"" to
request exclusive creation. (Contributed by Serhiy Storchaka in
bpo-21717.)


Other module-level changes
==========================

Many functions in the "mmap", "ossaudiodev", "socket", "ssl", and
"codecs" modules now accept writable *bytes-like objects*.
(Contributed by Serhiy Storchaka in bpo-23001.)


Optimizations
=============

The "os.walk()" function has been sped up by 3 to 5 times on POSIX
systems, and by 7 to 20 times on Windows.  This was done using the new
"os.scandir()" function, which exposes file information from the
underlying "readdir" or "FindFirstFile"/"FindNextFile" system calls.
(Contributed by Ben Hoyt with help from Victor Stinner in bpo-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. (Contributed by
Victor Stinner in bpo-21233.)

Some operations on "ipaddress" "IPv4Network" and "IPv6Network" have
been massively sped up, such as "subnets()", "supernet()",
"summarize_address_range()", "collapse_addresses()". The speed up can
range from 3 to 15 times. (Contributed by Antoine Pitrou, Michel
Albert, and Markus in bpo-21486, bpo-21487, bpo-20826, bpo-23266.)

Pickling of "ipaddress" objects was optimized to produce significantly
smaller output.  (Contributed by Serhiy Storchaka in bpo-23133.)

Many operations on "io.BytesIO" are now 50% to 100% faster.
(Contributed by Serhiy Storchaka in bpo-15381 and David Wilson in
bpo-22003.)

The "marshal.dumps()" function is now faster: 65--85% with versions 3
and 4, 20--25% with versions 0 to 2 on typical data, and up to 5 times
in best cases. (Contributed by Serhiy Storchaka in bpo-20416 and
bpo-23344.)

The UTF-32 encoder is now 3 to 7 times faster. (Contributed by Serhiy
Storchaka in bpo-15027.)

Regular expressions are now parsed up to 10% faster. (Contributed by
Serhiy Storchaka in bpo-19380.)

The "json.dumps()" function was optimized to run with
"ensure_ascii=False" as fast as with "ensure_ascii=True". (Contributed
by Naoki Inada in bpo-23206.)

The "PyObject_IsInstance()" and "PyObject_IsSubclass()" functions have
been sped up in the common case that the second argument has "type" as
its metaclass. (Contributed Georg Brandl by in bpo-22540.)

Method caching was slightly improved, yielding up to 5% performance
improvement in some benchmarks. (Contributed by Antoine Pitrou in
bpo-22847.)

Objects from the "random" module now use 50% less memory on 64-bit
builds.  (Contributed by Serhiy Storchaka in bpo-23488.)

The "property()" getter calls are up to 25% faster. (Contributed by
Joe Jevnik in bpo-23910.)

Instantiation of "fractions.Fraction" is now up to 30% faster.
(Contributed by Stefan Behnel in bpo-22464.)

String methods "find()", "rfind()", "split()", "partition()" and the
"in" string operator are now significantly faster for searching
1-character substrings. (Contributed by Serhiy Storchaka in
bpo-23573.)


Build and C API Changes
=======================

New "calloc" functions were added:

* "PyMem_RawCalloc()",

* "PyMem_Calloc()",

* "PyObject_Calloc()".

(Contributed by Victor Stinner in bpo-21233.)

New encoding/decoding helper functions:

* "Py_DecodeLocale()" (replaced "_Py_char2wchar()"),

* "Py_EncodeLocale()" (replaced "_Py_wchar2char()").