What’s New In Python 3.5
|Date:||March 29, 2015
This article explains the new features in Python 3.5, compared to 3.4.
For full details, see the Misc/NEWS file.
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.
PEP 478 - Python 3.5 Release Schedule
Summary – Release highlights
New syntax features:
New library modules:
New built-in features:
- 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
Significantly Improved Library Modules:
Please read on for a comprehensive list of user-facing changes.
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.
PEP 471 – os.scandir() function – a better and faster directory
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.
PEP 475 – Retry system calls failing with EINTR
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.
PEP 486 – Make the Python Launcher aware of virtual environments
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)
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
$ python -m zipapp myapp
$ python myapp.pyz
- FieldStorage now supports the context management protocol.
(Contributed by Berker Peksag in issue 20289.)
- 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.)
- 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.)
- iglob() and glob() now support recursive search in
subdirectories using the “**” pattern.
(Contributed by Serhiy Storchaka in issue 13968.)
- 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.)
- 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.)
- 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.)
- 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.)
- 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
- A new auth() method provides a convenient way to
implement custom authentication mechanisms.
(Contributed by Milan Oberkirch in issue 15014.)
- The user scripts directory on Windows is now versioned.
(Contributed by Paul Moore in issue 23437.)
- 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
(Contributed by Matej Cepl in issue 19494.)
- 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.)
The following performance enhancements have been added:
Build and C API Changes
Changes to Python’s build process and to the C API include:
Unsupported Operating Systems
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,
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.
Deprecated functions and types of the C API
API and Feature Removals
The following obsolete and previously deprecated APIs and features have been
- 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
- PEP 475: the following functions are now retried when interrupted instead
of raising InterruptedError if the signal handler does not raise
- 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
- 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 no 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)
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.