What’s New In Python 3.5

Release:3.5.0a0 Date:February 06, 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:

• None yet.

New library modules:

• None yet.

New built-in features:

• None yet.

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).

Significantly Improved Library Modules:

• None yet.

Security improvements:

• None yet.

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

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.)

New Modules

• None yet.

Improved Modules

cgi

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

code

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

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.)

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.)

doctest

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

glob

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

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.)

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 class method inspect.Signature.from_callable(), which makes subclassing of Signature easier. (Contributed by Yury Selivanov and Eric Snow in issue 17373.)

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.)

os

• os.stat_result now has a st_file_attributes attribute on Windows. (Contributed by Ben Hoyt in issue 21719.)

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.)

math

• math.inf and math.nan constants added. (Contributed by Mark Dickinson in issue 23185.)

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

• 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. (Contributed by Maciej Szulik in issue 19662.)
• 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.)
• SMTPServer now supports RFC 6531 via the enable_SMTPUTF8 constructor argument and a user-provided process_smtputf8_message() method.

smtplib

• A new auth() method provides a convenient way to implement custom authentication mechanisms. (Contributed by Milan Oberkirch in issue 15014.)

sndhdr

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

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.)

time

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

time

• A new urllib.request.HTTPBasicPriorAuthHandler allows HTTP Basic Authentication credentials to be sent unconditionally with the first HTTP request, rather than waiting for a HTTP 401 Unauthorized response from the server. (Contributed by Matej Cepl in issue 19494.)

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.)

Optimizations

The following performance enhancements have been added:

• Construction of bytes(int) (filled by zero bytes) is faster and use 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.)

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()

Deprecated

Unsupported Operating Systems

• None yet.

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.

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.)

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

• 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.

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.