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****************************
What's New In Python 3.2
****************************
:Author: Raymond Hettinger
:Release: |release|
:Date: |today|
.. $Id$
Rules for maintenance:
* Anyone can add text to this document. Do not spend very much time
on the wording of your changes, because your text will probably
get rewritten. (Note, during release candidate phase or just before
a beta release, please use the tracker instead -- this helps avoid
merge conflicts. If you must add a suggested entry directly,
please put it in an XXX comment and the maintainer will take notice).
* The maintainer will go through Misc/NEWS periodically and add
changes; it's therefore more important to add your changes to
Misc/NEWS than to this file.
* This is not a complete list of every single change; completeness
is the purpose of Misc/NEWS. Some changes I consider too small
or esoteric to include. If such a change is added to the text,
I'll just remove it. (This is another reason you shouldn't spend
too much time on writing your addition.)
* If you want to draw your new text to the attention of the
maintainer, add 'XXX' to the beginning of the paragraph or
section.
* It's OK to just add a fragmentary note about a change. For
example: "XXX Describe the transmogrify() function added to the
socket module." The maintainer will research the change and
write the necessary text.
* You can comment out your additions if you like, but it's not
necessary (especially when a final release is some months away).
* Credit the author of a patch or bugfix. Just the name is
sufficient; the e-mail address isn't necessary. It's helpful to
add the issue number:
XXX Describe the transmogrify() function added to the socket
module.
(Contributed by P.Y. Developer; :issue:`12345`.)
This saves the maintainer the effort of going through the SVN log
when researching a change.
This article explains the new features in Python 3.2 as compared to 3.1. It
focuses on a few highlights and gives a few examples. For full details, see the
:source:`Misc/NEWS <Misc/NEWS>` file.
.. seealso::
:pep:`392` - Python 3.2 Release Schedule
PEP 384: Defining a Stable ABI
==============================
In the past, extension modules built for one Python version were often
not usable with other Python versions. Particularly on Windows, every
feature release of Python required rebuilding all extension modules that
one wanted to use. This requirement was the result of the free access to
Python interpreter internals that extension modules could use.
With Python 3.2, an alternative approach becomes available: extension
modules which restrict themselves to a limited API (by defining
Py_LIMITED_API) cannot use many of the internals, but are constrained
to a set of API functions that are promised to be stable for several
releases. As a consequence, extension modules built for 3.2 in that
mode will also work with 3.3, 3.4, and so on. Extension modules that
make use of details of memory structures can still be built, but will
need to be recompiled for every feature release.
.. seealso::
:pep:`384` - Defining a Stable ABI
PEP written by Martin von Löwis.
PEP 389: Argparse Command Line Parsing Module
=============================================
A new module for command line parsing, :mod:`argparse`, was introduced to
overcome the limitations of :mod:`optparse` which did not provide support for
positional arguments (not just options), subcommands, required options and other
common patterns of specifying and validating options.
This module has already had widespread success in the community as a
third-party module. Being more fully featured than its predecessor, the
:mod:`argparse` module is now the preferred module for command-line processing.
The older module is still being kept available because of the substantial amount
of legacy code that depends on it.
Here's an annotated example parser showing features like limiting results to a
set of choices, specifying a *metavar* in the help screen, validating that one
or more positional arguments is present, and making a required option::
import argparse
parser = argparse.ArgumentParser(
description = 'Manage servers', # main description for help
epilog = 'Tested on Solaris and Linux') # displayed after help
parser.add_argument('action', # argument name
choices = ['deploy', 'start', 'stop'], # three allowed values
help = 'action on each target') # help msg
parser.add_argument('targets',
metavar = 'HOSTNAME', # var name used in help msg
nargs = '+', # require one or more targets
help = 'url for target machines') # help msg explanation
parser.add_argument('-u', '--user', # -u or --user option
required = True, # make it a required argument
help = 'login as user')
Example of calling the parser on a command string::
>>> cmd = 'deploy sneezy.example.com sleepy.example.com -u skycaptain'
>>> result = parser.parse_args(cmd.split())
>>> result.action
'deploy'
>>> result.targets
['sneezy.example.com', 'sleepy.example.com']
>>> result.user
'skycaptain'
Example of the parser's automatically generated help::
>>> parser.parse_args('-h'.split())
usage: manage_cloud.py [-h] -u USER
{deploy,start,stop} HOSTNAME [HOSTNAME ...]
Manage servers
positional arguments:
{deploy,start,stop} action on each target
HOSTNAME url for target machines
optional arguments:
-h, --help show this help message and exit
-u USER, --user USER login as user
Tested on Solaris and Linux
An especially nice :mod:`argparse` feature is the ability to define subparsers,
each with their own argument patterns and help displays::
import argparse
parser = argparse.ArgumentParser(prog='HELM')
subparsers = parser.add_subparsers()
parser_l = subparsers.add_parser('launch', help='Launch Control') # first subgroup
parser_l.add_argument('-m', '--missiles', action='store_true')
parser_l.add_argument('-t', '--torpedos', action='store_true')
parser_m = subparsers.add_parser('move', help='Move Vessel', # second subgroup
aliases=('steer', 'turn')) # equivalent names
parser_m.add_argument('-c', '--course', type=int, required=True)
parser_m.add_argument('-s', '--speed', type=int, default=0)
$ ./helm.py --help # top level help (launch and move)
$ ./helm.py launch --help # help for launch options
$ ./helm.py launch --missiles # set missiles=True and torpedos=False
$ ./helm.py steer --course 180 --speed 5 # set movement parameters
.. seealso::
:pep:`389` - New Command Line Parsing Module
PEP written by Steven Bethard.
:ref:`upgrading-optparse-code` for details on the differences from :mod:`optparse`.
PEP 391: Dictionary Based Configuration for Logging
====================================================
The :mod:`logging` module provided two kinds of configuration, one style with
function calls for each option or another style driven by an external file saved
in a :mod:`ConfigParser` format. Those options did not provide the flexibility
to create configurations from JSON or YAML files, nor did they support
incremental configuration, which is needed for specifying logger options from a
command line.
To support a more flexible style, the module now offers
:func:`logging.config.dictConfig` for specifying logging configuration with
plain Python dictionaries. The configuration options include formatters,
handlers, filters, and loggers. Here's a working example of a configuration
dictionary::
{"version": 1,
"formatters": {"brief": {"format": "%(levelname)-8s: %(name)-15s: %(message)s"},
"full": {"format": "%(asctime)s %(name)-15s %(levelname)-8s %(message)s"}
},
"handlers": {"console": {
"class": "logging.StreamHandler",
"formatter": "brief",
"level": "INFO",
"stream": "ext://sys.stdout"},
"console_priority": {
"class": "logging.StreamHandler",
"formatter": "full",
"level": "ERROR",
"stream": "ext://sys.stderr"}
},
"root": {"level": "DEBUG", "handlers": ["console", "console_priority"]}}
If that dictionary is stored in a file called :file:`conf.json`, it can be
loaded and called with code like this::
>>> import json, logging.config
>>> with open('conf.json') as f:
conf = json.load(f)
>>> logging.config.dictConfig(conf)
>>> logging.info("Transaction completed normally")
INFO : root : Transaction completed normally
>>> logging.critical("Abnormal termination")
2011-02-17 11:14:36,694 root CRITICAL Abnormal termination
.. seealso::
:pep:`391` - Dictionary Based Configuration for Logging
PEP written by Vinay Sajip.
PEP 3148: The ``concurrent.futures`` module
============================================
Code for creating and managing concurrency is being collected in a new top-level
namespace, *concurrent*. Its first member is a *futures* package which provides
a uniform high-level interface for managing threads and processes.
The design for :mod:`concurrent.futures` was inspired by the
*java.util.concurrent* package. In that model, a running call and its result
are represented by a :class:`~concurrent.futures.Future` object that abstracts
features common to threads, processes, and remote procedure calls. That object
supports status checks (running or done), timeouts, cancellations, adding
callbacks, and access to results or exceptions.
The primary offering of the new module is a pair of executor classes for
launching and managing calls. The goal of the executors is to make it easier to
use existing tools for making parallel calls. They save the effort needed to
setup a pool of resources, launch the calls, create a results queue, add
time-out handling, and limit the total number of threads, processes, or remote
procedure calls.
Ideally, each application should share a single executor across multiple
components so that process and thread limits can be centrally managed. This
solves the design challenge that arises when each component has its own
competing strategy for resource management.
Both classes share a common interface with three methods:
:meth:`~concurrent.futures.Executor.submit` for scheduling a callable and
returning a :class:`~concurrent.futures.Future` object;
:meth:`~concurrent.futures.Executor.map` for scheduling many asynchronous calls
at a time, and :meth:`~concurrent.futures.Executor.shutdown` for freeing
resources. The class is a :term:`context manager` and can be used in a
:keyword:`with` statement to assure that resources are automatically released
when currently pending futures are done executing.
A simple of example of :class:`~concurrent.futures.ThreadPoolExecutor` is a
launch of four parallel threads for copying files::
import concurrent.futures, shutil
with concurrent.futures.ThreadPoolExecutor(max_workers=4) as e:
e.submit(shutil.copy, 'src1.txt', 'dest1.txt')
e.submit(shutil.copy, 'src2.txt', 'dest2.txt')
e.submit(shutil.copy, 'src3.txt', 'dest3.txt')
e.submit(shutil.copy, 'src4.txt', 'dest4.txt')
.. seealso::
:pep:`3148` - Futures -- Execute Computations Asynchronously
PEP written by Brian Quinlan.
:ref:`Code for Threaded Parallel URL reads<threadpoolexecutor-example>`, an
example using threads to fetch multiple web pages in parallel.
:ref:`Code for computing prime numbers in
parallel<processpoolexecutor-example>`, an example demonstrating
:class:`~concurrent.futures.ProcessPoolExecutor`.
PEP 3147: PYC Repository Directories
=====================================
Python's scheme for caching bytecode in *.pyc* files did not work well in
environments with multiple Python interpreters. If one interpreter encountered
a cached file created by another interpreter, it would recompile the source and
overwrite the cached file, thus losing the benefits of caching.
The issue of "pyc fights" has become more pronounced as it has become
commonplace for Linux distributions to ship with multiple versions of Python.
These conflicts also arise with CPython alternatives such as Unladen Swallow.
To solve this problem, Python's import machinery has been extended to use
distinct filenames for each interpreter. Instead of Python 3.2 and Python 3.3 and
Unladen Swallow each competing for a file called "mymodule.pyc", they will now
look for "mymodule.cpython-32.pyc", "mymodule.cpython-33.pyc", and
"mymodule.unladen10.pyc". And to prevent all of these new files from
cluttering source directories, the *pyc* files are now collected in a
"__pycache__" directory stored under the package directory.
Aside from the filenames and target directories, the new scheme has a few
aspects that are visible to the programmer:
* Imported modules now have a :attr:`__cached__` attribute which stores the name
of the actual file that was imported:
>>> import collections
>>> collections.__cached__
'c:/py32/lib/__pycache__/collections.cpython-32.pyc'
* The tag that is unique to each interpreter is accessible from the :mod:`imp`
module:
>>> import imp
>>> imp.get_tag()
'cpython-32'
* Scripts that try to deduce source filename from the imported file now need to
be smarter. It is no longer sufficient to simply strip the "c" from a ".pyc"
filename. Instead, use the new functions in the :mod:`imp` module:
>>> imp.source_from_cache('c:/py32/lib/__pycache__/collections.cpython-32.pyc')
'c:/py32/lib/collections.py'
>>> imp.cache_from_source('c:/py32/lib/collections.py')
'c:/py32/lib/__pycache__/collections.cpython-32.pyc'
* The :mod:`py_compile` and :mod:`compileall` modules have been updated to
reflect the new naming convention and target directory. The command-line
invocation of *compileall* has new options: ``-i`` for
specifying a list of files and directories to compile and ``-b`` which causes
bytecode files to be written to their legacy location rather than
*__pycache__*.
* The :mod:`importlib.abc` module has been updated with new :term:`abstract base
classes <abstract base class>` for loading bytecode files. The obsolete
ABCs, :class:`~importlib.abc.PyLoader` and
:class:`~importlib.abc.PyPycLoader`, have been deprecated (instructions on how
to stay Python 3.1 compatible are included with the documentation).
.. seealso::
:pep:`3147` - PYC Repository Directories
PEP written by Barry Warsaw.
PEP 3149: ABI Version Tagged .so Files
======================================
The PYC repository directory allows multiple bytecode cache files to be
co-located. This PEP implements a similar mechanism for shared object files by
giving them a common directory and distinct names for each version.
The common directory is "pyshared" and the file names are made distinct by
identifying the Python implementation (such as CPython, PyPy, Jython, etc.), the
major and minor version numbers, and optional build flags (such as "d" for
debug, "m" for pymalloc, "u" for wide-unicode). For an arbitrary package "foo",
you may see these files when the distribution package is installed::
/usr/share/pyshared/foo.cpython-32m.so
/usr/share/pyshared/foo.cpython-33md.so
In Python itself, the tags are accessible from functions in the :mod:`sysconfig`
module::
>>> import sysconfig
>>> sysconfig.get_config_var('SOABI') # find the version tag
'cpython-32mu'
>>> sysconfig.get_config_var('SO') # find the full filename extension
'.cpython-32mu.so'
.. seealso::
:pep:`3149` - ABI Version Tagged .so Files
PEP written by Barry Warsaw.
PEP 3333: Python Web Server Gateway Interface v1.0.1
=====================================================
This informational PEP clarifies how bytes/text issues are to be handled by the
WSGI protocol. The challenge is that string handling in Python 3 is most
conveniently handled with the :class:`str` type even though the HTTP protocol
is itself bytes oriented.
The PEP differentiates so-called *native strings* that are used for
request/response headers and metadata versus *byte strings* which are used for
the bodies of requests and responses.
The *native strings* are always of type :class:`str` but are restricted to code
points between *U+0000* through *U+00FF* which are translatable to bytes using
*Latin-1* encoding. These strings are used for the keys and values in the
environment dictionary and for response headers and statuses in the
:func:`start_response` function. They must follow :rfc:`2616` with respect to
encoding. That is, they must either be *ISO-8859-1* characters or use
:rfc:`2047` MIME encoding.
For developers porting WSGI applications from Python 2, here are the salient
points:
* If the app already used strings for headers in Python 2, no change is needed.
* If instead, the app encoded output headers or decoded input headers, then the
headers will need to be re-encoded to Latin-1. For example, an output header
encoded in utf-8 was using ``h.encode('utf-8')`` now needs to convert from
bytes to native strings using ``h.encode('utf-8').decode('latin-1')``.
* Values yielded by an application or sent using the :meth:`write` method
must be byte strings. The :func:`start_response` function and environ
must use native strings. The two cannot be mixed.
For server implementers writing CGI-to-WSGI pathways or other CGI-style
protocols, the users must to be able access the environment using native strings
even though the underlying platform may have a different convention. To bridge
this gap, the :mod:`wsgiref` module has a new function,
:func:`wsgiref.handlers.read_environ` for transcoding CGI variables from
:attr:`os.environ` into native strings and returning a new dictionary.
.. seealso::
:pep:`3333` - Python Web Server Gateway Interface v1.0.1
PEP written by Phillip Eby.
Other Language Changes
======================
Some smaller changes made to the core Python language are:
* String formatting for :func:`format` and :meth:`str.format` gained new
capabilities for the format character **#**. Previously, for integers in
binary, octal, or hexadecimal, it caused the output to be prefixed with '0b',
'0o', or '0x' respectively. Now it can also handle floats, complex, and
Decimal, causing the output to always have a decimal point even when no digits
follow it.
>>> format(20, '#o')
'0o24'
>>> format(12.34, '#5.0f')
' 12.'
(Suggested by Mark Dickinson and implemented by Eric Smith in :issue:`7094`.)
* There is also a new :meth:`str.format_map` method that extends the
capabilities of the existing :meth:`str.format` method by accepting arbitrary
:term:`mapping` objects. This new method makes it possible to use string
formatting with any of Python's many dictionary-like objects such as
:class:`~collections.defaultdict`, :class:`~shelve.Shelf`,
:class:`~configparser.ConfigParser`, or :mod:`dbm`. It is also useful with
custom :class:`dict` subclasses that normalize keys before look-up or that
supply a :meth:`__missing__` method for unknown keys::
>>> import shelve
>>> d = shelve.open('tmp.shl')
>>> 'The {project_name} status is {status} as of {date}'.format_map(d)
'The testing project status is green as of February 15, 2011'
>>> class LowerCasedDict(dict):
def __getitem__(self, key):
return dict.__getitem__(self, key.lower())
>>> lcd = LowerCasedDict(part='widgets', quantity=10)
>>> 'There are {QUANTITY} {Part} in stock'.format_map(lcd)
'There are 10 widgets in stock'
>>> class PlaceholderDict(dict):
def __missing__(self, key):
return '<{}>'.format(key)
>>> 'Hello {name}, welcome to {location}'.format_map(PlaceholderDict())
'Hello <name>, welcome to <location>'
(Suggested by Raymond Hettinger and implemented by Eric Smith in
:issue:`6081`.)
* The interpreter can now be started with a quiet option, ``-q``, to prevent
the copyright and version information from being displayed in the interactive
mode. The option can be introspected using the :attr:`sys.flags` attribute::
$ python -q
>>> sys.flags
sys.flags(debug=0, division_warning=0, inspect=0, interactive=0,
optimize=0, dont_write_bytecode=0, no_user_site=0, no_site=0,
ignore_environment=0, verbose=0, bytes_warning=0, quiet=1)
(Contributed by Marcin Wojdyr in :issue:`1772833`).
* The :func:`hasattr` function works by calling :func:`getattr` and detecting
whether an exception is raised. This technique allows it to detect methods
created dynamically by :meth:`__getattr__` or :meth:`__getattribute__` which
would otherwise be absent from the class dictionary. Formerly, *hasattr*
would catch any exception, possibly masking genuine errors. Now, *hasattr*
has been tightened to only catch :exc:`AttributeError` and let other
exceptions pass through::
>>> class A:
@property
def f(self):
return 1 // 0
>>> a = A()
>>> hasattr(a, 'f')
Traceback (most recent call last):
...
ZeroDivisionError: integer division or modulo by zero
(Discovered by Yury Selivanov and fixed by Benjamin Peterson; :issue:`9666`.)
* The :func:`str` of a float or complex number is now the same as its
:func:`repr`. Previously, the :func:`str` form was shorter but that just
caused confusion and is no longer needed now that the shortest possible
:func:`repr` is displayed by default:
>>> import math
>>> repr(math.pi)
'3.141592653589793'
>>> str(math.pi)
'3.141592653589793'
(Proposed and implemented by Mark Dickinson; :issue:`9337`.)
* :class:`memoryview` objects now have a :meth:`~memoryview.release()` method
and they also now support the context manager protocol. This allows timely
release of any resources that were acquired when requesting a buffer from the
original object.
>>> with memoryview(b'abcdefgh') as v:
print(v.tolist())
[97, 98, 99, 100, 101, 102, 103, 104]
(Added by Antoine Pitrou; :issue:`9757`.)
* Previously it was illegal to delete a name from the local namespace if it
occurs as a free variable in a nested block::
def outer(x):
def inner():
return x
inner()
del x
This is now allowed. Remember that the target of an :keyword:`except` clause
is cleared, so this code which used to work with Python 2.6, raised a
:exc:`SyntaxError` with Python 3.1 and now works again::
def f():
def print_error():
print(e)
try:
something
except Exception as e:
print_error()
# implicit "del e" here
(See :issue:`4617`.)
* The internal :c:type:`structsequence` tool now creates subclasses of tuple.
This means that C structures like those returned by :func:`os.stat`,
:func:`time.gmtime`, and :attr:`sys.version_info` now work like a
:term:`named tuple` and now work with functions and methods that
expect a tuple as an argument. This is a big step forward in making the C
structures as flexible as their pure Python counterparts:
>>> isinstance(sys.version_info, tuple)
True
>>> 'Version %d.%d.%d %s(%d)' % sys.version_info
'Version 3.2.0 final(0)'
(Suggested by Arfrever Frehtes Taifersar Arahesis and implemented
by Benjamin Peterson in :issue:`8413`.)
* Warnings are now easier to control using the :envvar:`PYTHONWARNINGS`
environment variable as an alternative to using ``-W`` at the command line::
$ export PYTHONWARNINGS='ignore::RuntimeWarning::,once::UnicodeWarning::'
(Suggested by Barry Warsaw and implemented by Philip Jenvey in :issue:`7301`.)
* A new warning category, :exc:`ResourceWarning`, has been added. It is
emitted when potential issues with resource consumption or cleanup
are detected. It is silenced by default in normal release builds but
can be enabled through the means provided by the :mod:`warnings`
module, or on the command line.
A :exc:`ResourceWarning` is issued at interpreter shutdown if the
:data:`gc.garbage` list isn't empty, and if :attr:`gc.DEBUG_UNCOLLECTABLE` is
set, all uncollectable objects are printed. This is meant to make the
programmer aware that their code contains object finalization issues.
A :exc:`ResourceWarning` is also issued when a :term:`file object` is destroyed
without having been explicitly closed. While the deallocator for such
object ensures it closes the underlying operating system resource
(usually, a file descriptor), the delay in deallocating the object could
produce various issues, especially under Windows. Here is an example
of enabling the warning from the command line::
$ python -q -Wdefault
>>> f = open("foo", "wb")
>>> del f
__main__:1: ResourceWarning: unclosed file <_io.BufferedWriter name='foo'>
(Added by Antoine Pitrou and Georg Brandl in :issue:`10093` and :issue:`477863`.)
* :class:`range` objects now support *index* and *count* methods. This is part
of an effort to make more objects fully implement the
:class:`collections.Sequence` :term:`abstract base class`. As a result, the
language will have a more uniform API. In addition, :class:`range` objects
now support slicing and negative indices, even with values larger than
:attr:`sys.maxsize`. This makes *range* more interoperable with lists::
>>> range(0, 100, 2).count(10)
1
>>> range(0, 100, 2).index(10)
5
>>> range(0, 100, 2)[5]
10
>>> range(0, 100, 2)[0:5]
range(0, 10, 2)
(Contributed by Daniel Stutzbach in :issue:`9213`, by Alexander Belopolsky
in :issue:`2690`, and by Nick Coghlan in :issue:`10889`.)
* The :func:`callable` builtin function from Py2.x was resurrected. It provides
a concise, readable alternative to using an :term:`abstract base class` in an
expression like ``isinstance(x, collections.Callable)``:
>>> callable(max)
True
>>> callable(20)
False
(See :issue:`10518`.)
* Python's import mechanism can now load modules installed in directories with
non-ASCII characters in the path name. This solved an aggravating problem
with home directories for users with non-ASCII characters in their usernames.
(Required extensive work by Victor Stinner in :issue:`9425`.)
New, Improved, and Deprecated Modules
=====================================
Python's standard library has undergone significant maintenance efforts and
quality improvements.
The biggest news for Python 3.2 is that the :mod:`email` package, :mod:`mailbox`
module, and :mod:`nntplib` modules now work correctly with the bytes/text model
in Python 3. For the first time, there is correct handling of messages with
mixed encodings.
Throughout the standard library, there has been more careful attention to
encodings and text versus bytes issues. In particular, interactions with the
operating system are now better able to exchange non-ASCII data using the
Windows MBCS encoding, locale-aware encodings, or UTF-8.
Another significant win is the addition of substantially better support for
*SSL* connections and security certificates.
In addition, more classes now implement a :term:`context manager` to support
convenient and reliable resource clean-up using a :keyword:`with` statement.
email
-----
The usability of the :mod:`email` package in Python 3 has been mostly fixed by
the extensive efforts of R. David Murray. The problem was that emails are
typically read and stored in the form of :class:`bytes` rather than :class:`str`
text, and they may contain multiple encodings within a single email. So, the
email package had to be extended to parse and generate email messages in bytes
format.
* New functions :func:`~email.message_from_bytes` and
:func:`~email.message_from_binary_file`, and new classes
:class:`~email.parser.BytesFeedParser` and :class:`~email.parser.BytesParser`
allow binary message data to be parsed into model objects.
* Given bytes input to the model, :meth:`~email.message.Message.get_payload`
will by default decode a message body that has a
:mailheader:`Content-Transfer-Encoding` of *8bit* using the charset
specified in the MIME headers and return the resulting string.
* Given bytes input to the model, :class:`~email.generator.Generator` will
convert message bodies that have a :mailheader:`Content-Transfer-Encoding` of
*8bit* to instead have a *7bit* :mailheader:`Content-Transfer-Encoding`.
Headers with unencoded non-ASCII bytes are deemed to be :rfc:`2047`\ -encoded
using the *unknown-8bit* character set.
* A new class :class:`~email.generator.BytesGenerator` produces bytes as output,
preserving any unchanged non-ASCII data that was present in the input used to
build the model, including message bodies with a
:mailheader:`Content-Transfer-Encoding` of *8bit*.
* The :mod:`smtplib` :class:`~smtplib.SMTP` class now accepts a byte string
for the *msg* argument to the :meth:`~smtplib.SMTP.sendmail` method,
and a new method, :meth:`~smtplib.SMTP.send_message` accepts a
:class:`~email.message.Message` object and can optionally obtain the
*from_addr* and *to_addrs* addresses directly from the object.
(Proposed and implemented by R. David Murray, :issue:`4661` and :issue:`10321`.)
elementtree
-----------
The :mod:`xml.etree.ElementTree` package and its :mod:`xml.etree.cElementTree`
counterpart have been updated to version 1.3.
Several new and useful functions and methods have been added:
* :func:`xml.etree.ElementTree.fromstringlist` which builds an XML document
from a sequence of fragments
* :func:`xml.etree.ElementTree.register_namespace` for registering a global
namespace prefix
* :func:`xml.etree.ElementTree.tostringlist` for string representation
including all sublists
* :meth:`xml.etree.ElementTree.Element.extend` for appending a sequence of zero
or more elements
* :meth:`xml.etree.ElementTree.Element.iterfind` searches an element and
subelements
* :meth:`xml.etree.ElementTree.Element.itertext` creates a text iterator over
an element and its subelements
* :meth:`xml.etree.ElementTree.TreeBuilder.end` closes the current element
* :meth:`xml.etree.ElementTree.TreeBuilder.doctype` handles a doctype
declaration
Two methods have been deprecated:
* :meth:`xml.etree.ElementTree.getchildren` use ``list(elem)`` instead.
* :meth:`xml.etree.ElementTree.getiterator` use ``Element.iter`` instead.
For details of the update, see `Introducing ElementTree
<http://effbot.org/zone/elementtree-13-intro.htm>`_ on Fredrik Lundh's website.
(Contributed by Florent Xicluna and Fredrik Lundh, :issue:`6472`.)
functools
---------
* The :mod:`functools` module includes a new decorator for caching function
calls. :func:`functools.lru_cache` can save repeated queries to an external
resource whenever the results are expected to be the same.
For example, adding a caching decorator to a database query function can save
database accesses for popular searches:
>>> import functools
>>> @functools.lru_cache(maxsize=300)
>>> def get_phone_number(name):
c = conn.cursor()
c.execute('SELECT phonenumber FROM phonelist WHERE name=?', (name,))
return c.fetchone()[0]
>>> for name in user_requests:
get_phone_number(name) # cached lookup
To help with choosing an effective cache size, the wrapped function is
instrumented for tracking cache statistics:
>>> get_phone_number.cache_info()
CacheInfo(hits=4805, misses=980, maxsize=300, currsize=300)
If the phonelist table gets updated, the outdated contents of the cache can be
cleared with:
>>> get_phone_number.cache_clear()
(Contributed by Raymond Hettinger and incorporating design ideas from Jim
Baker, Miki Tebeka, and Nick Coghlan; see `recipe 498245
<http://code.activestate.com/recipes/498245>`_\, `recipe 577479
<http://code.activestate.com/recipes/577479>`_\, :issue:`10586`, and
:issue:`10593`.)
* The :func:`functools.wraps` decorator now adds a :attr:`__wrapped__` attribute
pointing to the original callable function. This allows wrapped functions to
be introspected. It also copies :attr:`__annotations__` if defined. And now
it also gracefully skips over missing attributes such as :attr:`__doc__` which
might not be defined for the wrapped callable.
In the above example, the cache can be removed by recovering the original
function:
>>> get_phone_number = get_phone_number.__wrapped__ # uncached function
(By Nick Coghlan and Terrence Cole; :issue:`9567`, :issue:`3445`, and
:issue:`8814`.)
* To help write classes with rich comparison methods, a new decorator
:func:`functools.total_ordering` will use a existing equality and inequality
methods to fill in the remaining methods.
For example, supplying *__eq__* and *__lt__* will enable
:func:`~functools.total_ordering` to fill-in *__le__*, *__gt__* and *__ge__*::
@total_ordering
class Student:
def __eq__(self, other):
return ((self.lastname.lower(), self.firstname.lower()) ==
(other.lastname.lower(), other.firstname.lower()))
def __lt__(self, other):
return ((self.lastname.lower(), self.firstname.lower()) <
(other.lastname.lower(), other.firstname.lower()))
With the *total_ordering* decorator, the remaining comparison methods
are filled in automatically.
(Contributed by Raymond Hettinger.)
* To aid in porting programs from Python 2, the :func:`functools.cmp_to_key`
function converts an old-style comparison function to
modern :term:`key function`:
>>> # locale-aware sort order
>>> sorted(iterable, key=cmp_to_key(locale.strcoll))
For sorting examples and a brief sorting tutorial, see the `Sorting HowTo
<http://wiki.python.org/moin/HowTo/Sorting/>`_ tutorial.
(Contributed by Raymond Hettinger.)
itertools
---------
* The :mod:`itertools` module has a new :func:`~itertools.accumulate` function
modeled on APL's *scan* operator and Numpy's *accumulate* function:
>>> from itertools import accumulate
>>> list(accumulate([8, 2, 50]))
[8, 10, 60]
>>> prob_dist = [0.1, 0.4, 0.2, 0.3]
>>> list(accumulate(prob_dist)) # cumulative probability distribution
[0.1, 0.5, 0.7, 1.0]
For an example using :func:`~itertools.accumulate`, see the :ref:`examples for
the random module <random-examples>`.
(Contributed by Raymond Hettinger and incorporating design suggestions
from Mark Dickinson.)
collections
-----------
* The :class:`collections.Counter` class now has two forms of in-place
subtraction, the existing *-=* operator for `saturating subtraction
<http://en.wikipedia.org/wiki/Saturation_arithmetic>`_ and the new
:meth:`~collections.Counter.subtract` method for regular subtraction. The
former is suitable for `multisets <http://en.wikipedia.org/wiki/Multiset>`_
which only have positive counts, and the latter is more suitable for use cases
that allow negative counts:
>>> tally = Counter(dogs=5, cat=3)
>>> tally -= Counter(dogs=2, cats=8) # saturating subtraction
>>> tally
Counter({'dogs': 3})
>>> tally = Counter(dogs=5, cats=3)
>>> tally.subtract(dogs=2, cats=8) # regular subtraction
>>> tally
Counter({'dogs': 3, 'cats': -5})
(Contributed by Raymond Hettinger.)
* The :class:`collections.OrderedDict` class has a new method
:meth:`~collections.OrderedDict.move_to_end` which takes an existing key and
moves it to either the first or last position in the ordered sequence.
The default is to move an item to the last position. This is equivalent of
renewing an entry with ``od[k] = od.pop(k)``.
A fast move-to-end operation is useful for resequencing entries. For example,
an ordered dictionary can be used to track order of access by aging entries
from the oldest to the most recently accessed.
>>> d = OrderedDict.fromkeys(['a', 'b', 'X', 'd', 'e'])
>>> list(d)
['a', 'b', 'X', 'd', 'e']
>>> d.move_to_end('X')
>>> list(d)
['a', 'b', 'd', 'e', 'X']
(Contributed by Raymond Hettinger.)
* The :class:`collections.deque` class grew two new methods
:meth:`~collections.deque.count` and :meth:`~collections.deque.reverse` that
make them more substitutable for :class:`list` objects:
>>> d = deque('simsalabim')
>>> d.count('s')
2
>>> d.reverse()
>>> d
deque(['m', 'i', 'b', 'a', 'l', 'a', 's', 'm', 'i', 's'])
(Contributed by Raymond Hettinger.)
threading
---------
The :mod:`threading` module has a new :class:`~threading.Barrier`
synchronization class for making multiple threads wait until all of them have
reached a common barrier point. Barriers are useful for making sure that a task
with multiple preconditions does not run until all of the predecessor tasks are
complete.
Barriers can work with an arbitrary number of threads. This is a generalization
of a `Rendezvous <http://en.wikipedia.org/wiki/Synchronous_rendezvous>`_ which
is defined for only two threads.
Implemented as a two-phase cyclic barrier, :class:`~threading.Barrier` objects
are suitable for use in loops. The separate *filling* and *draining* phases
assure that all threads get released (drained) before any one of them can loop
back and re-enter the barrier. The barrier fully resets after each cycle.
Example of using barriers::
from threading import Barrier, Thread
def get_votes(site):
ballots = conduct_election(site)
all_polls_closed.wait() # do not count until all polls are closed
totals = summarize(ballots)
publish(site, totals)
all_polls_closed = Barrier(len(sites))
for site in sites:
Thread(target=get_votes, args=(site,)).start()
In this example, the barrier enforces a rule that votes cannot be counted at any
polling site until all polls are closed. Notice how a solution with a barrier
is similar to one with :meth:`threading.Thread.join`, but the threads stay alive
and continue to do work (summarizing ballots) after the barrier point is
crossed.
If any of the predecessor tasks can hang or be delayed, a barrier can be created
with an optional *timeout* parameter. Then if the timeout period elapses before
all the predecessor tasks reach the barrier point, all waiting threads are
released and a :exc:`~threading.BrokenBarrierError` exception is raised::
def get_votes(site):
ballots = conduct_election(site)
try:
all_polls_closed.wait(timeout = midnight - time.now())
except BrokenBarrierError:
lockbox = seal_ballots(ballots)
queue.put(lockbox)
else:
totals = summarize(ballots)
publish(site, totals)
In this example, the barrier enforces a more robust rule. If some election
sites do not finish before midnight, the barrier times-out and the ballots are
sealed and deposited in a queue for later handling.
See `Barrier Synchronization Patterns
<http://parlab.eecs.berkeley.edu/wiki/_media/patterns/paraplop_g1_3.pdf>`_ for
more examples of how barriers can be used in parallel computing. Also, there is
a simple but thorough explanation of barriers in `The Little Book of Semaphores
<http://greenteapress.com/semaphores/downey08semaphores.pdf>`_, *section 3.6*.
(Contributed by Kristján Valur Jónsson with an API review by Jeffrey Yasskin in
:issue:`8777`.)
datetime and time
-----------------
* The :mod:`datetime` module has a new type :class:`~datetime.timezone` that
implements the :class:`~datetime.tzinfo` interface by returning a fixed UTC
offset and timezone name. This makes it easier to create timezone-aware
datetime objects::
>>> from datetime import datetime, timezone
>>> datetime.now(timezone.utc)
datetime.datetime(2010, 12, 8, 21, 4, 2, 923754, tzinfo=datetime.timezone.utc)
>>> datetime.strptime("01/01/2000 12:00 +0000", "%m/%d/%Y %H:%M %z")
datetime.datetime(2000, 1, 1, 12, 0, tzinfo=datetime.timezone.utc)
* Also, :class:`~datetime.timedelta` objects can now be multiplied by
:class:`float` and divided by :class:`float` and :class:`int` objects.
And :class:`~datetime.timedelta` objects can now divide one another.
* The :meth:`datetime.date.strftime` method is no longer restricted to years
after 1900. The new supported year range is from 1000 to 9999 inclusive.
* Whenever a two-digit year is used in a time tuple, the interpretation has been
governed by :attr:`time.accept2dyear`. The default is *True* which means that
for a two-digit year, the century is guessed according to the POSIX rules
governing the ``%y`` strptime format.
Starting with Py3.2, use of the century guessing heuristic will emit a
:exc:`DeprecationWarning`. Instead, it is recommended that
:attr:`time.accept2dyear` be set to *False* so that large date ranges
can be used without guesswork::
>>> import time, warnings
>>> warnings.resetwarnings() # remove the default warning filters
>>> time.accept2dyear = True # guess whether 11 means 11 or 2011
>>> time.asctime((11, 1, 1, 12, 34, 56, 4, 1, 0))
Warning (from warnings module):
...
DeprecationWarning: Century info guessed for a 2-digit year.
'Fri Jan 1 12:34:56 2011'
>>> time.accept2dyear = False # use the full range of allowable dates
>>> time.asctime((11, 1, 1, 12, 34, 56, 4, 1, 0))
'Fri Jan 1 12:34:56 11'
Several functions now have significantly expanded date ranges. When
:attr:`time.accept2dyear` is false, the :func:`time.asctime` function will
accept any year that fits in a C int, while the :func:`time.mktime` and
:func:`time.strftime` functions will accept the full range supported by the
corresponding operating system functions.
(Contributed by Alexander Belopolsky and Victor Stinner in :issue:`1289118`,
:issue:`5094`, :issue:`6641`, :issue:`2706`, :issue:`1777412`, :issue:`8013`,
and :issue:`10827`.)
.. XXX http://bugs.python.org/issue?%40search_text=datetime&%40sort=-activity
math
----
The :mod:`math` module has been updated with six new functions inspired by the
C99 standard.
The :func:`~math.isfinite` function provides a reliable and fast way to detect
special values. It returns *True* for regular numbers and *False* for *Nan* or
*Infinity*:
>>> [isfinite(x) for x in (123, 4.56, float('Nan'), float('Inf'))]
[True, True, False, False]
The :func:`~math.expm1` function computes ``e**x-1`` for small values of *x*
without incurring the loss of precision that usually accompanies the subtraction
of nearly equal quantities:
>>> expm1(0.013671875) # more accurate way to compute e**x-1 for a small x
0.013765762467652909
The :func:`~math.erf` function computes a probability integral or `Gaussian
error function <http://en.wikipedia.org/wiki/Error_function>`_. The
complementary error function, :func:`~math.erfc`, is ``1 - erf(x)``:
>>> erf(1.0/sqrt(2.0)) # portion of normal distribution within 1 standard deviation
0.682689492137086
>>> erfc(1.0/sqrt(2.0)) # portion of normal distribution outside 1 standard deviation
0.31731050786291404
>>> erf(1.0/sqrt(2.0)) + erfc(1.0/sqrt(2.0))
1.0
The :func:`~math.gamma` function is a continuous extension of the factorial
function. See http://en.wikipedia.org/wiki/Gamma_function for details. Because
the function is related to factorials, it grows large even for small values of
*x*, so there is also a :func:`~math.lgamma` function for computing the natural
logarithm of the gamma function:
>>> gamma(7.0) # six factorial
720.0
>>> lgamma(801.0) # log(800 factorial)
4551.950730698041
(Contributed by Mark Dickinson.)
abc
---
The :mod:`abc` module now supports :func:`~abc.abstractclassmethod` and
:func:`~abc.abstractstaticmethod`.
These tools make it possible to define an :term:`abstract base class` that
requires a particular :func:`classmethod` or :func:`staticmethod` to be
implemented::
class Temperature(metaclass=abc.ABCMeta):
@abc.abstractclassmethod
def from_fahrenheit(cls, t):
...
@abc.abstractclassmethod
def from_celsius(cls, t):
...
(Patch submitted by Daniel Urban; :issue:`5867`.)
io
--
The :class:`io.BytesIO` has a new method, :meth:`~io.BytesIO.getbuffer`, which
provides functionality similar to :func:`memoryview`. It creates an editable
view of the data without making a copy. The buffer's random access and support
for slice notation are well-suited to in-place editing::
>>> REC_LEN, LOC_START, LOC_LEN = 34, 7, 11
>>> def change_location(buffer, record_number, location):
start = record_number * REC_LEN + LOC_START
buffer[start: start+LOC_LEN] = location
>>> import io
>>> byte_stream = io.BytesIO(
b'G3805 storeroom Main chassis '
b'X7899 shipping Reserve cog '
b'L6988 receiving Primary sprocket'
)
>>> buffer = byte_stream.getbuffer()
>>> change_location(buffer, 1, b'warehouse ')
>>> change_location(buffer, 0, b'showroom ')
>>> print(byte_stream.getvalue())
b'G3805 showroom Main chassis '
b'X7899 warehouse Reserve cog '
b'L6988 receiving Primary sprocket'
(Contributed by Antoine Pitrou in :issue:`5506`.)
reprlib
-------
When writing a :meth:`__repr__` method for a custom container, it is easy to
forget to handle the case where a member refers back to the container itself.
Python's builtin objects such as :class:`list` and :class:`set` handle
self-reference by displaying "..." in the recursive part of the representation
string.
To help write such :meth:`__repr__` methods, the :mod:`reprlib` module has a new
decorator, :func:`~reprlib.recursive_repr`, for detecting recursive calls to
:meth:`__repr__` and substituting a placeholder string instead::
>>> class MyList(list):
@recursive_repr()
def __repr__(self):
return '<' + '|'.join(map(repr, self)) + '>'
>>> m = MyList('abc')
>>> m.append(m)
>>> m.append('x')
>>> print(m)
<'a'|'b'|'c'|...|'x'>
(Contributed by Raymond Hettinger in :issue:`9826` and :issue:`9840`.)
logging
-------
In addition to dictionary-based configuration described above, the
:mod:`logging` package has many other improvements.
The logging documentation has been augmented by a :ref:`basic tutorial
<logging-basic-tutorial>`\, an :ref:`advanced tutorial
<logging-advanced-tutorial>`\, and a :ref:`cookbook <logging-cookbook>` of
logging recipes. These documents are the fastest way to learn about logging.
The :func:`logging.basicConfig` set-up function gained a *style* argument to
support three different types of string formatting. It defaults to "%" for
traditional %-formatting, can be set to "{" for the new :meth:`str.format` style, or
can be set to "$" for the shell-style formatting provided by
:class:`string.Template`. The following three configurations are equivalent::
>>> from logging import basicConfig
>>> basicConfig(style='%', format="%(name)s -> %(levelname)s: %(message)s")
>>> basicConfig(style='{', format="{name} -> {levelname} {message}")
>>> basicConfig(style='$', format="$name -> $levelname: $message")
If no configuration is set-up before a logging event occurs, there is now a
default configuration using a :class:`~logging.StreamHandler` directed to
:attr:`sys.stderr` for events of ``WARNING`` level or higher. Formerly, an
event occurring before a configuration was set-up would either raise an
exception or silently drop the event depending on the value of
:attr:`logging.raiseExceptions`. The new default handler is stored in
:attr:`logging.lastResort`.
The use of filters has been simplified. Instead of creating a
:class:`~logging.Filter` object, the predicate can be any Python callable that
returns *True* or *False*.
There were a number of other improvements that add flexibility and simplify
configuration. See the module documentation for a full listing of changes in
Python 3.2.
csv
---
The :mod:`csv` module now supports a new dialect, :class:`~csv.unix_dialect`,
which applies quoting for all fields and a traditional Unix style with ``'\n'`` as
the line terminator. The registered dialect name is ``unix``.
The :class:`csv.DictWriter` has a new method,
:meth:`~csv.DictWriter.writeheader` for writing-out an initial row to document
the field names::
>>> import csv, sys
>>> w = csv.DictWriter(sys.stdout, ['name', 'dept'], dialect='unix')
>>> w.writeheader()
"name","dept"
>>> w.writerows([
{'name': 'tom', 'dept': 'accounting'},
{'name': 'susan', 'dept': 'Salesl'}])
"tom","accounting"
"susan","sales"
(New dialect suggested by Jay Talbot in :issue:`5975`, and the new method
suggested by Ed Abraham in :issue:`1537721`.)
contextlib
----------
There is a new and slightly mind-blowing tool
:class:`~contextlib.ContextDecorator` that is helpful for creating a
:term:`context manager` that does double duty as a function decorator.
As a convenience, this new functionality is used by
:func:`~contextlib.contextmanager` so that no extra effort is needed to support
both roles.
The basic idea is that both context managers and function decorators can be used
for pre-action and post-action wrappers. Context managers wrap a group of
statements using a :keyword:`with` statement, and function decorators wrap a
group of statements enclosed in a function. So, occasionally there is a need to
write a pre-action or post-action wrapper that can be used in either role.
For example, it is sometimes useful to wrap functions or groups of statements
with a logger that can track the time of entry and time of exit. Rather than
writing both a function decorator and a context manager for the task, the
:func:`~contextlib.contextmanager` provides both capabilities in a single
definition::
from contextlib import contextmanager
import logging
logging.basicConfig(level=logging.INFO)
@contextmanager
def track_entry_and_exit(name):
logging.info('Entering: {}'.format(name))
yield
logging.info('Exiting: {}'.format(name))
Formerly, this would have only been usable as a context manager::
with track_entry_and_exit('widget loader'):
print('Some time consuming activity goes here')
load_widget()
Now, it can be used as a decorator as well::
@track_entry_and_exit('widget loader')
def activity():
print('Some time consuming activity goes here')
load_widget()
Trying to fulfill two roles at once places some limitations on the technique.
Context managers normally have the flexibility to return an argument usable by
a :keyword:`with` statement, but there is no parallel for function decorators.
In the above example, there is not a clean way for the *track_entry_and_exit*
context manager to return a logging instance for use in the body of enclosed
statements.
(Contributed by Michael Foord in :issue:`9110`.)
decimal and fractions
---------------------
Mark Dickinson crafted an elegant and efficient scheme for assuring that
different numeric datatypes will have the same hash value whenever their actual
values are equal (:issue:`8188`)::
assert hash(Fraction(3, 2)) == hash(1.5) == \
hash(Decimal("1.5")) == hash(complex(1.5, 0))
Some of the hashing details are exposed through a new attribute,
:attr:`sys.hash_info`, which describes the bit width of the hash value, the
prime modulus, the hash values for *infinity* and *nan*, and the multiplier
used for the imaginary part of a number:
>>> sys.hash_info
sys.hash_info(width=64, modulus=2305843009213693951, inf=314159, nan=0, imag=1000003)
An early decision to limit the inter-operability of various numeric types has
been relaxed. It is still unsupported (and ill-advised) to have implicit
mixing in arithmetic expressions such as ``Decimal('1.1') + float('1.1')``
because the latter loses information in the process of constructing the binary
float. However, since existing floating point value can be converted losslessly
to either a decimal or rational representation, it makes sense to add them to
the constructor and to support mixed-type comparisons.
* The :class:`decimal.Decimal` constructor now accepts :class:`float` objects
directly so there in no longer a need to use the :meth:`~decimal.Decimal.from_float`
method (:issue:`8257`).
* Mixed type comparisons are now fully supported so that
:class:`~decimal.Decimal` objects can be directly compared with :class:`float`
and :class:`fractions.Fraction` (:issue:`2531` and :issue:`8188`).
Similar changes were made to :class:`fractions.Fraction` so that the
:meth:`~fractions.Fraction.from_float()` and :meth:`~fractions.Fraction.from_decimal`
methods are no longer needed (:issue:`8294`):
>>> Decimal(1.1)
Decimal('1.100000000000000088817841970012523233890533447265625')
>>> Fraction(1.1)
Fraction(2476979795053773, 2251799813685248)
Another useful change for the :mod:`decimal` module is that the
:attr:`Context.clamp` attribute is now public. This is useful in creating
contexts that correspond to the decimal interchange formats specified in IEEE
754 (see :issue:`8540`).
(Contributed by Mark Dickinson and Raymond Hettinger.)
ftp
---
The :class:`ftplib.FTP` class now supports the context manager protocol to
unconditionally consume :exc:`socket.error` exceptions and to close the FTP
connection when done::
>>> from ftplib import FTP
>>> with FTP("ftp1.at.proftpd.org") as ftp:
ftp.login()
ftp.dir()
'230 Anonymous login ok, restrictions apply.'
dr-xr-xr-x 9 ftp ftp 154 May 6 10:43 .
dr-xr-xr-x 9 ftp ftp 154 May 6 10:43 ..
dr-xr-xr-x 5 ftp ftp 4096 May 6 10:43 CentOS
dr-xr-xr-x 3 ftp ftp 18 Jul 10 2008 Fedora
Other file-like objects such as :class:`mmap.mmap` and :func:`fileinput.input`
also grew auto-closing context managers::
with fileinput.input(files=('log1.txt', 'log2.txt')) as f:
for line in f:
process(line)
(Contributed by Tarek Ziadé and Giampaolo Rodolà in :issue:`4972`, and
by Georg Brandl in :issue:`8046` and :issue:`1286`.)
The :class:`~ftplib.FTP_TLS` class now accepts a *context* parameter, which is a
:class:`ssl.SSLContext` object allowing bundling SSL configuration options,
certificates and private keys into a single (potentially long-lived) structure.
(Contributed by Giampaolo Rodolà; :issue:`8806`.)
popen
-----
The :func:`os.popen` and :func:`subprocess.Popen` functions now support
:keyword:`with` statements for auto-closing of the file descriptors.
(Contributed by Antoine Pitrou and Brian Curtin in :issue:`7461` and
:issue:`10554`.)
select
------
The :mod:`select` module now exposes a new, constant attribute,
:attr:`~select.PIPE_BUF`, which gives the minimum number of bytes which are
guaranteed not to block when :func:`select.select` says a pipe is ready
for writing.
>>> import select
>>> select.PIPE_BUF
512
(Available on Unix systems. Patch by Sébastien Sablé in :issue:`9862`)
gzip and zipfile
----------------
:class:`gzip.GzipFile` now implements the :class:`io.BufferedIOBase`
:term:`abstract base class` (except for ``truncate()``). It also has a
:meth:`~gzip.GzipFile.peek` method and supports unseekable as well as
zero-padded file objects.
The :mod:`gzip` module also gains the :func:`~gzip.compress` and
:func:`~gzip.decompress` functions for easier in-memory compression and
decompression. Keep in mind that text needs to be encoded as :class:`bytes`
before compressing and decompressing:
>>> s = 'Three shall be the number thou shalt count, '
>>> s += 'and the number of the counting shall be three'
>>> b = s.encode() # convert to utf-8
>>> len(b)
89
>>> c = gzip.compress(b)
>>> len(c)
77
>>> gzip.decompress(c).decode()[:42] # decompress and convert to text
'Three shall be the number thou shalt count,'
(Contributed by Anand B. Pillai in :issue:`3488`; and by Antoine Pitrou, Nir
Aides and Brian Curtin in :issue:`9962`, :issue:`1675951`, :issue:`7471` and
:issue:`2846`.)
Also, the :class:`zipfile.ZipExtFile` class was reworked internally to represent
files stored inside an archive. The new implementation is significantly faster
and can be wrapped in a :class:`io.BufferedReader` object for more speedups. It
also solves an issue where interleaved calls to *read* and *readline* gave the
wrong results.
(Patch submitted by Nir Aides in :issue:`7610`.)
tarfile
-------
The :class:`~tarfile.TarFile` class can now be used as a context manager. In
addition, its :meth:`~tarfile.TarFile.add` method has a new option, *filter*,
that controls which files are added to the archive and allows the file metadata
to be edited.
The new *filter* option replaces the older, less flexible *exclude* parameter
which is now deprecated. If specified, the optional *filter* parameter needs to
be a :term:`keyword argument`. The user-supplied filter function accepts a
:class:`~tarfile.TarInfo` object and returns an updated
:class:`~tarfile.TarInfo` object, or if it wants the file to be excluded, the
function can return *None*::
>>> import tarfile, glob
>>> def myfilter(tarinfo):
if tarinfo.isfile(): # only save real files
tarinfo.uname = 'monty' # redact the user name
return tarinfo
>>> with tarfile.open(name='myarchive.tar.gz', mode='w:gz') as tf:
for filename in glob.glob('*.txt'):
tf.add(filename, filter=myfilter)
tf.list()
-rw-r--r-- monty/501 902 2011-01-26 17:59:11 annotations.txt
-rw-r--r-- monty/501 123 2011-01-26 17:59:11 general_questions.txt
-rw-r--r-- monty/501 3514 2011-01-26 17:59:11 prion.txt
-rw-r--r-- monty/501 124 2011-01-26 17:59:11 py_todo.txt
-rw-r--r-- monty/501 1399 2011-01-26 17:59:11 semaphore_notes.txt
(Proposed by Tarek Ziadé and implemented by Lars Gustäbel in :issue:`6856`.)
hashlib
-------
The :mod:`hashlib` module has two new constant attributes listing the hashing
algorithms guaranteed to be present in all implementations and those available
on the current implementation::
>>> import hashlib
>>> hashlib.algorithms_guaranteed
{'sha1', 'sha224', 'sha384', 'sha256', 'sha512', 'md5'}
>>> hashlib.algorithms_available
{'md2', 'SHA256', 'SHA512', 'dsaWithSHA', 'mdc2', 'SHA224', 'MD4', 'sha256',
'sha512', 'ripemd160', 'SHA1', 'MDC2', 'SHA', 'SHA384', 'MD2',
'ecdsa-with-SHA1','md4', 'md5', 'sha1', 'DSA-SHA', 'sha224',
'dsaEncryption', 'DSA', 'RIPEMD160', 'sha', 'MD5', 'sha384'}
(Suggested by Carl Chenet in :issue:`7418`.)
ast
---
The :mod:`ast` module has a wonderful a general-purpose tool for safely
evaluating expression strings using the Python literal
syntax. The :func:`ast.literal_eval` function serves as a secure alternative to
the builtin :func:`eval` function which is easily abused. Python 3.2 adds
:class:`bytes` and :class:`set` literals to the list of supported types:
strings, bytes, numbers, tuples, lists, dicts, sets, booleans, and None.
::
>>> from ast import literal_eval
>>> request = "{'req': 3, 'func': 'pow', 'args': (2, 0.5)}"
>>> literal_eval(request)
{'args': (2, 0.5), 'req': 3, 'func': 'pow'}
>>> request = "os.system('do something harmful')"
>>> literal_eval(request)
Traceback (most recent call last):
...
ValueError: malformed node or string: <_ast.Call object at 0x101739a10>
(Implemented by Benjamin Peterson and Georg Brandl.)
os
--
Different operating systems use various encodings for filenames and environment
variables. The :mod:`os` module provides two new functions,
:func:`~os.fsencode` and :func:`~os.fsdecode`, for encoding and decoding
filenames:
>>> filename = 'Sehenswürdigkeiten'
>>> os.fsencode(filename)
b'Sehensw\xc3\xbcrdigkeiten'
Some operating systems allow direct access to encoded bytes in the
environment. If so, the :attr:`os.supports_bytes_environ` constant will be
true.
For direct access to encoded environment variables (if available),
use the new :func:`os.getenvb` function or use :data:`os.environb`
which is a bytes version of :data:`os.environ`.
(Contributed by Victor Stinner.)
shutil
------
The :func:`shutil.copytree` function has two new options:
* *ignore_dangling_symlinks*: when ``symlinks=False`` so that the function
copies a file pointed to by a symlink, not the symlink itself. This option
will silence the error raised if the file doesn't exist.
* *copy_function*: is a callable that will be used to copy files.
:func:`shutil.copy2` is used by default.
(Contributed by Tarek Ziadé.)
In addition, the :mod:`shutil` module now supports :ref:`archiving operations
<archiving-operations>` for zipfiles, uncompressed tarfiles, gzipped tarfiles,
and bzipped tarfiles. And there are functions for registering additional
archiving file formats (such as xz compressed tarfiles or custom formats).
The principal functions are :func:`~shutil.make_archive` and
:func:`~shutil.unpack_archive`. By default, both operate on the current
directory (which can be set by :func:`os.chdir`) and on any sub-directories.
The archive filename needs to be specified with a full pathname. The archiving
step is non-destructive (the original files are left unchanged).
::
>>> import shutil, pprint
>>> os.chdir('mydata') # change to the source directory
>>> f = shutil.make_archive('/var/backup/mydata',
'zip') # archive the current directory
>>> f # show the name of archive
'/var/backup/mydata.zip'
>>> os.chdir('tmp') # change to an unpacking
>>> shutil.unpack_archive('/var/backup/mydata.zip') # recover the data
>>> pprint.pprint(shutil.get_archive_formats()) # display known formats
[('bztar', "bzip2'ed tar-file"),
('gztar', "gzip'ed tar-file"),
('tar', 'uncompressed tar file'),
('zip', 'ZIP file')]
>>> shutil.register_archive_format( # register a new archive format
name = 'xz',
function = xz.compress, # callable archiving function
extra_args = [('level', 8)], # arguments to the function
description = 'xz compression'
)
(Contributed by Tarek Ziadé.)
sqlite3
-------
The :mod:`sqlite3` module was updated to pysqlite version 2.6.0. It has two new capabilities.
* The :attr:`sqlite3.Connection.in_transit` attribute is true if there is an
active transaction for uncommitted changes.
* The :meth:`sqlite3.Connection.enable_load_extension` and
:meth:`sqlite3.Connection.load_extension` methods allows you to load SQLite
extensions from ".so" files. One well-known extension is the fulltext-search
extension distributed with SQLite.
(Contributed by R. David Murray and Shashwat Anand; :issue:`8845`.)
html
----
A new :mod:`html` module was introduced with only a single function,
:func:`~html.escape`, which is used for escaping reserved characters from HTML
markup:
>>> import html
>>> html.escape('x > 2 && x < 7')
'x &gt; 2 &amp;&amp; x &lt; 7'
socket
------
The :mod:`socket` module has two new improvements.
* Socket objects now have a :meth:`~socket.socket.detach()` method which puts
the socket into closed state without actually closing the underlying file
descriptor. The latter can then be reused for other purposes.
(Added by Antoine Pitrou; :issue:`8524`.)
* :func:`socket.create_connection` now supports the context manager protocol
to unconditionally consume :exc:`socket.error` exceptions and to close the
socket when done.
(Contributed by Giampaolo Rodolà; :issue:`9794`.)
ssl
---
The :mod:`ssl` module added a number of features to satisfy common requirements
for secure (encrypted, authenticated) internet connections:
* A new class, :class:`~ssl.SSLContext`, serves as a container for persistent
SSL data, such as protocol settings, certificates, private keys, and various
other options. It includes a :meth:`~ssl.SSLContext.wrap_socket` for creating
an SSL socket from an SSL context.
* A new function, :func:`ssl.match_hostname`, supports server identity
verification for higher-level protocols by implementing the rules of HTTPS
(from :rfc:`2818`) which are also suitable for other protocols.
* The :func:`ssl.wrap_socket` constructor function now takes a *ciphers*
argument. The *ciphers* string lists the allowed encryption algorithms using
the format described in the `OpenSSL documentation
<http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT>`__.
* When linked against recent versions of OpenSSL, the :mod:`ssl` module now
supports the Server Name Indication extension to the TLS protocol, allowing
multiple "virtual hosts" using different certificates on a single IP port.
This extension is only supported in client mode, and is activated by passing
the *server_hostname* argument to :meth:`ssl.SSLContext.wrap_socket`.
* Various options have been added to the :mod:`ssl` module, such as
:data:`~ssl.OP_NO_SSLv2` which disables the insecure and obsolete SSLv2
protocol.
* The extension now loads all the OpenSSL ciphers and digest algorithms. If
some SSL certificates cannot be verified, they are reported as an "unknown
algorithm" error.
* The version of OpenSSL being used is now accessible using the module
attributes :data:`ssl.OPENSSL_VERSION` (a string),
:data:`ssl.OPENSSL_VERSION_INFO` (a 5-tuple), and
:data:`ssl.OPENSSL_VERSION_NUMBER` (an integer).
(Contributed by Antoine Pitrou in :issue:`8850`, :issue:`1589`, :issue:`8322`,
:issue:`5639`, :issue:`4870`, :issue:`8484`, and :issue:`8321`.)
nntp
----
The :mod:`nntplib` module has a revamped implementation with better bytes and
text semantics as well as more practical APIs. These improvements break
compatibility with the nntplib version in Python 3.1, which was partly
dysfunctional in itself.
Support for secure connections through both implicit (using
:class:`nntplib.NNTP_SSL`) and explicit (using :meth:`nntplib.NNTP.starttls`)
TLS has also been added.
(Contributed by Antoine Pitrou in :issue:`9360` and Andrew Vant in :issue:`1926`.)
certificates
------------
:class:`http.client.HTTPSConnection`, :class:`urllib.request.HTTPSHandler`
and :func:`urllib.request.urlopen` now take optional arguments to allow for
server certificate checking against a set of Certificate Authorities,
as recommended in public uses of HTTPS.
(Added by Antoine Pitrou, :issue:`9003`.)
imaplib
-------
Support for explicit TLS on standard IMAP4 connections has been added through
the new :mod:`imaplib.IMAP4.starttls` method.
(Contributed by Lorenzo M. Catucci and Antoine Pitrou, :issue:`4471`.)
http.client
-----------
There were a number of small API improvements in the :mod:`http.client` module.
The old-style HTTP 0.9 simple responses are no longer supported and the *strict*
parameter is deprecated in all classes.
The :class:`~http.client.HTTPConnection` and
:class:`~http.client.HTTPSConnection` classes now have a *source_address*
parameter for a (host, port) tuple indicating where the HTTP connection is made
from.
Support for certificate checking and HTTPS virtual hosts were added to
:class:`~http.client.HTTPSConnection`.
The :meth:`~http.client.HTTPConnection.request` method on connection objects
allowed an optional *body* argument so that a :term:`file object` could be used
to supply the content of the request. Conveniently, the *body* argument now
also accepts an :term:`iterable` object so long as it includes an explicit
``Content-Length`` header. This extended interface is much more flexible than
before.
To establish an HTTPS connection through a proxy server, there is a new
:meth:`~http.client.HTTPConnection.set_tunnel` method that sets the host and
port for HTTP Connect tunneling.
To match the behavior of :mod:`http.server`, the HTTP client library now also
encodes headers with ISO-8859-1 (Latin-1) encoding. It was already doing that
for incoming headers, so now the behavior is consistent for both incoming and
outgoing traffic. (See work by Armin Ronacher in :issue:`10980`.)
unittest
--------
The unittest module has a number of improvements supporting test discovery for
packages, easier experimentation at the interactive prompt, new testcase
methods, improved diagnostic messages for test failures, and better method
names.
* The command-line call ``python -m unittest`` can now accept file paths
instead of module names for running specific tests (:issue:`10620`). The new
test discovery can find tests within packages, locating any test importable
from the top-level directory. The top-level directory can be specified with
the `-t` option, a pattern for matching files with ``-p``, and a directory to
start discovery with ``-s``::
$ python -m unittest discover -s my_proj_dir -p _test.py
(Contributed by Michael Foord.)
* Experimentation at the interactive prompt is now easier because the
:class:`unittest.case.TestCase` class can now be instantiated without
arguments:
>>> TestCase().assertEqual(pow(2, 3), 8)
(Contributed by Michael Foord.)
* The :mod:`unittest` module has two new methods,
:meth:`~unittest.TestCase.assertWarns` and
:meth:`~unittest.TestCase.assertWarnsRegex` to verify that a given warning type
is triggered by the code under test::
with self.assertWarns(DeprecationWarning):
legacy_function('XYZ')
(Contributed by Antoine Pitrou, :issue:`9754`.)
Another new method, :meth:`~unittest.TestCase.assertCountEqual` is used to
compare two iterables to determine if their element counts are equal (whether
the same elements are present with the same number of occurrences regardless
of order)::
def test_anagram(self):
self.assertCountEqual('algorithm', 'logarithm')
(Contributed by Raymond Hettinger.)
* A principal feature of the unittest module is an effort to produce meaningful
diagnostics when a test fails. When possible, the failure is recorded along
with a diff of the output. This is especially helpful for analyzing log files
of failed test runs. However, since diffs can sometime be voluminous, there is
a new :attr:`~unittest.TestCase.maxDiff` attribute that sets maximum length of
diffs displayed.
* In addition, the method names in the module have undergone a number of clean-ups.
For example, :meth:`~unittest.TestCase.assertRegex` is the new name for
:meth:`~unittest.TestCase.assertRegexpMatches` which was misnamed because the
test uses :func:`re.search`, not :func:`re.match`. Other methods using
regular expressions are now named using short form "Regex" in preference to
"Regexp" -- this matches the names used in other unittest implementations,
matches Python's old name for the :mod:`re` module, and it has unambiguous
camel-casing.
(Contributed by Raymond Hettinger and implemented by Ezio Melotti.)
* To improve consistency, some long-standing method aliases are being
deprecated in favor of the preferred names:
=============================== ==============================
Old Name Preferred Name
=============================== ==============================
:meth:`assert_` :meth:`.assertTrue`
:meth:`assertEquals` :meth:`.assertEqual`
:meth:`assertNotEquals` :meth:`.assertNotEqual`
:meth:`assertAlmostEquals` :meth:`.assertAlmostEqual`
:meth:`assertNotAlmostEquals` :meth:`.assertNotAlmostEqual`
=============================== ==============================
Likewise, the ``TestCase.fail*`` methods deprecated in Python 3.1 are expected
to be removed in Python 3.3. Also see the :ref:`deprecated-aliases` section in
the :mod:`unittest` documentation.
(Contributed by Ezio Melotti; :issue:`9424`.)
* The :meth:`~unittest.TestCase.assertDictContainsSubset` method was deprecated
because it was misimplemented with the arguments in the wrong order. This
created hard-to-debug optical illusions where tests like
``TestCase().assertDictContainsSubset({'a':1, 'b':2}, {'a':1})`` would fail.
(Contributed by Raymond Hettinger.)
random
------
The integer methods in the :mod:`random` module now do a better job of producing
uniform distributions. Previously, they computed selections with
``int(n*random())`` which had a slight bias whenever *n* was not a power of two.
Now, multiple selections are made from a range up to the next power of two and a
selection is kept only when it falls within the range ``0 <= x < n``. The
functions and methods affected are :func:`~random.randrange`,
:func:`~random.randint`, :func:`~random.choice`, :func:`~random.shuffle` and
:func:`~random.sample`.
(Contributed by Raymond Hettinger; :issue:`9025`.)
poplib
------
:class:`~poplib.POP3_SSL` class now accepts a *context* parameter, which is a
:class:`ssl.SSLContext` object allowing bundling SSL configuration options,
certificates and private keys into a single (potentially long-lived)
structure.
(Contributed by Giampaolo Rodolà; :issue:`8807`.)
asyncore
--------
:class:`asyncore.dispatcher` now provides a
:meth:`~asyncore.dispatcher.handle_accepted()` method
returning a `(sock, addr)` pair which is called when a connection has actually
been established with a new remote endpoint. This is supposed to be used as a
replacement for old :meth:`~asyncore.dispatcher.handle_accept()` and avoids
the user to call :meth:`~asyncore.dispatcher.accept()` directly.
(Contributed by Giampaolo Rodolà; :issue:`6706`.)
tempfile
--------
The :mod:`tempfile` module has a new context manager,
:class:`~tempfile.TemporaryDirectory` which provides easy deterministic
cleanup of temporary directories::
with tempfile.TemporaryDirectory() as tmpdirname:
print('created temporary dir:', tmpdirname)
(Contributed by Neil Schemenauer and Nick Coghlan; :issue:`5178`.)
inspect
-------
* The :mod:`inspect` module has a new function
:func:`~inspect.getgeneratorstate` to easily identify the current state of a
generator-iterator::
>>> from inspect import getgeneratorstate
>>> def gen():
yield 'demo'
>>> g = gen()
>>> getgeneratorstate(g)
'GEN_CREATED'
>>> next(g)
'demo'
>>> getgeneratorstate(g)
'GEN_SUSPENDED'
>>> next(g, None)
>>> getgeneratorstate(g)
'GEN_CLOSED'
(Contributed by Rodolpho Eckhardt and Nick Coghlan, :issue:`10220`.)
* To support lookups without the possibility of activating a dynamic attribute,
the :mod:`inspect` module has a new function, :func:`~inspect.getattr_static`.
Unlike :func:`hasattr`, this is a true read-only search, guaranteed not to
change state while it is searching::
>>> class A:
@property
def f(self):
print('Running')
return 10
>>> a = A()
>>> getattr(a, 'f')
Running
10
>>> inspect.getattr_static(a, 'f')
<property object at 0x1022bd788>
(Contributed by Michael Foord.)
pydoc
-----
The :mod:`pydoc` module now provides a much-improved Web server interface, as
well as a new command-line option ``-b`` to automatically open a browser window
to display that server::
$ pydoc3.2 -b
(Contributed by Ron Adam; :issue:`2001`.)
dis
---
The :mod:`dis` module gained two new functions for inspecting code,
:func:`~dis.code_info` and :func:`~dis.show_code`. Both provide detailed code
object information for the supplied function, method, source code string or code
object. The former returns a string and the latter prints it::
>>> import dis, random
>>> dis.show_code(random.choice)
Name: choice
Filename: /Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/random.py
Argument count: 2
Kw-only arguments: 0
Number of locals: 3
Stack size: 11
Flags: OPTIMIZED, NEWLOCALS, NOFREE
Constants:
0: 'Choose a random element from a non-empty sequence.'
1: 'Cannot choose from an empty sequence'
Names:
0: _randbelow
1: len
2: ValueError
3: IndexError
Variable names:
0: self
1: seq
2: i
In addition, the :func:`~dis.dis` function now accepts string arguments
so that the common idiom ``dis(compile(s, '', 'eval'))`` can be shortened
to ``dis(s)``::
>>> dis('3*x+1 if x%2==1 else x//2')
1 0 LOAD_NAME 0 (x)
3 LOAD_CONST 0 (2)
6 BINARY_MODULO
7 LOAD_CONST 1 (1)
10 COMPARE_OP 2 (==)
13 POP_JUMP_IF_FALSE 28
16 LOAD_CONST 2 (3)
19 LOAD_NAME 0 (x)
22 BINARY_MULTIPLY
23 LOAD_CONST 1 (1)
26 BINARY_ADD
27 RETURN_VALUE
>> 28 LOAD_NAME 0 (x)
31 LOAD_CONST 0 (2)
34 BINARY_FLOOR_DIVIDE
35 RETURN_VALUE
Taken together, these improvements make it easier to explore how CPython is
implemented and to see for yourself what the language syntax does
under-the-hood.
(Contributed by Nick Coghlan in :issue:`9147`.)
dbm
---
All database modules now support the :meth:`get` and :meth:`setdefault` methods.
(Suggested by Ray Allen in :issue:`9523`.)
ctypes
------
A new type, :class:`ctypes.c_ssize_t` represents the C :c:type:`ssize_t` datatype.
site
----
The :mod:`site` module has three new functions useful for reporting on the
details of a given Python installation.
* :func:`~site.getsitepackages` lists all global site-packages directories.
* :func:`~site.getuserbase` reports on the user's base directory where data can
be stored.
* :func:`~site.getusersitepackages` reveals the user-specific site-packages
directory path.
::
>>> import site
>>> site.getsitepackages()
['/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages',
'/Library/Frameworks/Python.framework/Versions/3.2/lib/site-python',
'/Library/Python/3.2/site-packages']
>>> site.getuserbase()
'/Users/raymondhettinger/Library/Python/3.2'
>>> site.getusersitepackages()
'/Users/raymondhettinger/Library/Python/3.2/lib/python/site-packages'
Conveniently, some of site's functionality is accessible directly from the
command-line::
$ python -m site --user-base
/Users/raymondhettinger/.local
$ python -m site --user-site
/Users/raymondhettinger/.local/lib/python3.2/site-packages
(Contributed by Tarek Ziadé in :issue:`6693`.)
sysconfig
---------
The new :mod:`sysconfig` module makes it straightforward to discover
installation paths and configuration variables that vary across platforms and
installations.
The module offers access simple access functions for platform and version
information:
* :func:`~sysconfig.get_platform` returning values like *linux-i586* or
*macosx-10.6-ppc*.
* :func:`~sysconfig.get_python_version` returns a Python version string
such as "3.2".
It also provides access to the paths and variables corresponding to one of
seven named schemes used by :mod:`distutils`. Those include *posix_prefix*,
*posix_home*, *posix_user*, *nt*, *nt_user*, *os2*, *os2_home*:
* :func:`~sysconfig.get_paths` makes a dictionary containing installation paths
for the current installation scheme.
* :func:`~sysconfig.get_config_vars` returns a dictionary of platform specific
variables.
There is also a convenient command-line interface::
C:\Python32>python -m sysconfig
Platform: "win32"
Python version: "3.2"
Current installation scheme: "nt"
Paths:
data = "C:\Python32"
include = "C:\Python32\Include"
platinclude = "C:\Python32\Include"
platlib = "C:\Python32\Lib\site-packages"
platstdlib = "C:\Python32\Lib"
purelib = "C:\Python32\Lib\site-packages"
scripts = "C:\Python32\Scripts"
stdlib = "C:\Python32\Lib"
Variables:
BINDIR = "C:\Python32"
BINLIBDEST = "C:\Python32\Lib"
EXE = ".exe"
INCLUDEPY = "C:\Python32\Include"
LIBDEST = "C:\Python32\Lib"
SO = ".pyd"
VERSION = "32"
abiflags = ""
base = "C:\Python32"
exec_prefix = "C:\Python32"
platbase = "C:\Python32"
prefix = "C:\Python32"
projectbase = "C:\Python32"
py_version = "3.2"
py_version_nodot = "32"
py_version_short = "3.2"
srcdir = "C:\Python32"
userbase = "C:\Documents and Settings\Raymond\Application Data\Python"
(Moved out of Distutils by Tarek Ziadé.)
pdb
---
The :mod:`pdb` debugger module gained a number of usability improvements:
* :file:`pdb.py` now has a ``-c`` option that executes commands as given in a
:file:`.pdbrc` script file.
* A :file:`.pdbrc` script file can contain ``continue`` and ``next`` commands
that continue debugging.
* The :class:`Pdb` class constructor now accepts a *nosigint* argument.
* New commands: ``l(list)``, ``ll(long list)`` and ``source`` for
listing source code.
* New commands: ``display`` and ``undisplay`` for showing or hiding
the value of an expression if it has changed.
* New command: ``interact`` for starting an interactive interpreter containing
the global and local names found in the current scope.
* Breakpoints can be cleared by breakpoint number.
(Contributed by Georg Brandl, Antonio Cuni and Ilya Sandler.)
configparser
------------
The :mod:`configparser` module was modified to improve usability and
predictability of the default parser and its supported INI syntax. The old
:class:`ConfigParser` class was removed in favor of :class:`SafeConfigParser`
which has in turn been renamed to :class:`~configparser.ConfigParser`. Support
for inline comments is now turned off by default and section or option
duplicates are not allowed in a single configuration source.
Config parsers gained a new API based on the mapping protocol::
>>> parser = ConfigParser()
>>> parser.read_string("""
[DEFAULT]
location = upper left
visible = yes
editable = no
color = blue
[main]
title = Main Menu
color = green
[options]
title = Options
""")
>>> parser['main']['color']
'green'
>>> parser['main']['editable']
'no'
>>> section = parser['options']
>>> section['title']
'Options'
>>> section['title'] = 'Options (editable: %(editable)s)'
>>> section['title']
'Options (editable: no)'
The new API is implemented on top of the classical API, so custom parser
subclasses should be able to use it without modifications.
The INI file structure accepted by config parsers can now be customized. Users
can specify alternative option/value delimiters and comment prefixes, change the
name of the *DEFAULT* section or switch the interpolation syntax.
There is support for pluggable interpolation including an additional interpolation
handler :class:`~configparser.ExtendedInterpolation`::
>>> parser = ConfigParser(interpolation=ExtendedInterpolation())
>>> parser.read_dict({'buildout': {'directory': '/home/ambv/zope9'},
'custom': {'prefix': '/usr/local'}})
>>> parser.read_string("""
[buildout]
parts =
zope9
instance
find-links =
${buildout:directory}/downloads/dist
[zope9]
recipe = plone.recipe.zope9install
location = /opt/zope
[instance]
recipe = plone.recipe.zope9instance
zope9-location = ${zope9:location}
zope-conf = ${custom:prefix}/etc/zope.conf
""")
>>> parser['buildout']['find-links']
'\n/home/ambv/zope9/downloads/dist'
>>> parser['instance']['zope-conf']
'/usr/local/etc/zope.conf'
>>> instance = parser['instance']
>>> instance['zope-conf']
'/usr/local/etc/zope.conf'
>>> instance['zope9-location']
'/opt/zope'
A number of smaller features were also introduced, like support for specifying
encoding in read operations, specifying fallback values for get-functions, or
reading directly from dictionaries and strings.
(All changes contributed by Łukasz Langa.)
.. XXX consider showing a difflib example
urllib.parse
------------
A number of usability improvements were made for the :mod:`urllib.parse` module.
The :func:`~urllib.parse.urlparse` function now supports `IPv6
<http://en.wikipedia.org/wiki/IPv6>`_ addresses as described in :rfc:`2732`:
>>> import urllib.parse
>>> urllib.parse.urlparse('http://[dead:beef:cafe:5417:affe:8FA3:deaf:feed]/foo/')
ParseResult(scheme='http',
netloc='[dead:beef:cafe:5417:affe:8FA3:deaf:feed]',
path='/foo/',
params='',
query='',
fragment='')
The :func:`~urllib.parse.urldefrag` function now returns a :term:`named tuple`::
>>> r = urllib.parse.urldefrag('http://python.org/about/#target')
>>> r
DefragResult(url='http://python.org/about/', fragment='target')
>>> r[0]
'http://python.org/about/'
>>> r.fragment
'target'
And, the :func:`~urllib.parse.urlencode` function is now much more flexible,
accepting either a string or bytes type for the *query* argument. If it is a
string, then the *safe*, *encoding*, and *error* parameters are sent to
:func:`~urllib.parse.quote_plus` for encoding::
>>> urllib.parse.urlencode([
('type', 'telenovela'),
('name', '¿Dónde Está Elisa?')],
encoding='latin-1')
'type=telenovela&name=%BFD%F3nde+Est%E1+Elisa%3F'
As detailed in :ref:`parsing-ascii-encoded-bytes`, all the :mod:`urllib.parse`
functions now accept ASCII-encoded byte strings as input, so long as they are
not mixed with regular strings. If ASCII-encoded byte strings are given as
parameters, the return types will also be an ASCII-encoded byte strings:
>>> urllib.parse.urlparse(b'http://www.python.org:80/about/')
ParseResultBytes(scheme=b'http', netloc=b'www.python.org:80',
path=b'/about/', params=b'', query=b'', fragment=b'')
(Work by Nick Coghlan, Dan Mahn, and Senthil Kumaran in :issue:`2987`,
:issue:`5468`, and :issue:`9873`.)
mailbox
-------
Thanks to a concerted effort by R. David Murray, the :mod:`mailbox` module has
been fixed for Python 3.2. The challenge was that mailbox had been originally
designed with a text interface, but email messages are best represented with
:class:`bytes` because various parts of a message may have different encodings.
The solution harnessed the :mod:`email` package's binary support for parsing
arbitrary email messages. In addition, the solution required a number of API
changes.
As expected, the :meth:`~mailbox.Mailbox.add` method for
:class:`mailbox.Mailbox` objects now accepts binary input.
:class:`~io.StringIO` and text file input are deprecated. Also, string input
will fail early if non-ASCII characters are used. Previously it would fail when
the email was processed in a later step.
There is also support for binary output. The :meth:`~mailbox.Mailbox.get_file`
method now returns a file in the binary mode (where it used to incorrectly set
the file to text-mode). There is also a new :meth:`~mailbox.Mailbox.get_bytes`
method that returns a :class:`bytes` representation of a message corresponding
to a given *key*.
It is still possible to get non-binary output using the old API's
:meth:`~mailbox.Mailbox.get_string` method, but that approach
is not very useful. Instead, it is best to extract messages from
a :class:`~mailbox.Message` object or to load them from binary input.
(Contributed by R. David Murray, with efforts from Steffen Daode Nurpmeso and an
initial patch by Victor Stinner in :issue:`9124`.)
turtledemo
----------
The demonstration code for the :mod:`turtle` module was moved from the *Demo*
directory to main library. It includes over a dozen sample scripts with
lively displays. Being on :attr:`sys.path`, it can now be run directly
from the command-line::
$ python -m turtledemo
(Moved from the Demo directory by Alexander Belopolsky in :issue:`10199`.)
Multi-threading
===============
* The mechanism for serializing execution of concurrently running Python threads
(generally known as the :term:`GIL` or :term:`Global Interpreter Lock`) has
been rewritten. Among the objectives were more predictable switching
intervals and reduced overhead due to lock contention and the number of
ensuing system calls. The notion of a "check interval" to allow thread
switches has been abandoned and replaced by an absolute duration expressed in
seconds. This parameter is tunable through :func:`sys.setswitchinterval()`.
It currently defaults to 5 milliseconds.
Additional details about the implementation can be read from a `python-dev
mailing-list message
<http://mail.python.org/pipermail/python-dev/2009-October/093321.html>`_
(however, "priority requests" as exposed in this message have not been kept
for inclusion).
(Contributed by Antoine Pitrou.)
* Regular and recursive locks now accept an optional *timeout* argument to their
:meth:`~threading.Lock.acquire` method. (Contributed by Antoine Pitrou;
:issue:`7316`.)
* Similarly, :meth:`threading.Semaphore.acquire` also gained a *timeout*
argument. (Contributed by Torsten Landschoff; :issue:`850728`.)
* Regular and recursive lock acquisitions can now be interrupted by signals on
platforms using Pthreads. This means that Python programs that deadlock while
acquiring locks can be successfully killed by repeatedly sending SIGINT to the
process (by pressing :kbd:`Ctrl+C` in most shells).
(Contributed by Reid Kleckner; :issue:`8844`.)
Optimizations
=============
A number of small performance enhancements have been added:
* Python's peephole optimizer now recognizes patterns such ``x in {1, 2, 3}`` as
being a test for membership in a set of constants. The optimizer recasts the
:class:`set` as a :class:`frozenset` and stores the pre-built constant.
Now that the speed penalty is gone, it is practical to start writing
membership tests using set-notation. This style is both semantically clear
and operationally fast::
extension = name.rpartition('.')[2]
if extension in {'xml', 'html', 'xhtml', 'css'}:
handle(name)
(Patch and additional tests contributed by Dave Malcolm; :issue:`6690`).
* Serializing and unserializing data using the :mod:`pickle` module is now
several times faster.
(Contributed by Alexandre Vassalotti, Antoine Pitrou
and the Unladen Swallow team in :issue:`9410` and :issue:`3873`.)
* The `Timsort algorithm <http://en.wikipedia.org/wiki/Timsort>`_ used in
:meth:`list.sort` and :func:`sorted` now runs faster and uses less memory
when called with a :term:`key function`. Previously, every element of
a list was wrapped with a temporary object that remembered the key value
associated with each element. Now, two arrays of keys and values are
sorted in parallel. This saves the memory consumed by the sort wrappers,
and it saves time lost to delegating comparisons.
(Patch by Daniel Stutzbach in :issue:`9915`.)
* JSON decoding performance is improved and memory consumption is reduced
whenever the same string is repeated for multiple keys. Also, JSON encoding
now uses the C speedups when the ``sort_keys`` argument is true.
(Contributed by Antoine Pitrou in :issue:`7451` and by Raymond Hettinger and
Antoine Pitrou in :issue:`10314`.)
* Recursive locks (created with the :func:`threading.RLock` API) now benefit
from a C implementation which makes them as fast as regular locks, and between
10x and 15x faster than their previous pure Python implementation.
(Contributed by Antoine Pitrou; :issue:`3001`.)
* The fast-search algorithm in stringlib is now used by the :meth:`split`,
:meth:`splitlines` and :meth:`replace` methods on
:class:`bytes`, :class:`bytearray` and :class:`str` objects. Likewise, the
algorithm is also used by :meth:`rfind`, :meth:`rindex`, :meth:`rsplit` and
:meth:`rpartition`.
(Patch by Florent Xicluna in :issue:`7622` and :issue:`7462`.)
* Integer to string conversions now work two "digits" at a time, reducing the
number of division and modulo operations.
(:issue:`6713` by Gawain Bolton, Mark Dickinson, and Victor Stinner.)
There were several other minor optimizations. Set differencing now runs faster
when one operand is much larger than the other (patch by Andress Bennetts in
:issue:`8685`). The :meth:`array.repeat` method has a faster implementation
(:issue:`1569291` by Alexander Belopolsky). The :class:`BaseHTTPRequestHandler`
has more efficient buffering (:issue:`3709` by Andrew Schaaf). The
:func:`operator.attrgetter` function has been sped-up (:issue:`10160` by
Christos Georgiou). And :class:`ConfigParser` loads multi-line arguments a bit
faster (:issue:`7113` by Łukasz Langa).
Unicode
=======
Python has been updated to `Unicode 6.0.0
<http://unicode.org/versions/Unicode6.0.0/>`_. The update to the standard adds
over 2,000 new characters including `emoji <http://en.wikipedia.org/wiki/Emoji>`_
symbols which are important for mobile phones.
In addition, the updated standard has altered the character properties for two
Kannada characters (U+0CF1, U+0CF2) and one New Tai Lue numeric character
(U+19DA), making the former eligible for use in identifiers while disqualifying
the latter. For more information, see `Unicode Character Database Changes
<http://www.unicode.org/versions/Unicode6.0.0/#Database_Changes>`_.
Codecs
======
Support was added for *cp720* Arabic DOS encoding (:issue:`1616979`).
MBCS encoding no longer ignores the error handler argument. In the default
strict mode, it raises an :exc:`UnicodeDecodeError` when it encounters an
undecodable byte sequence and an :exc:`UnicodeEncodeError` for an unencodable
character.
The MBCS codec supports ``'strict'`` and ``'ignore'`` error handlers for
decoding, and ``'strict'`` and ``'replace'`` for encoding.
To emulate Python3.1 MBCS encoding, select the ``'ignore'`` handler for decoding
and the ``'replace'`` handler for encoding.
On Mac OS X, Python decodes command line arguments with ``'utf-8'`` rather than
the locale encoding.
By default, :mod:`tarfile` uses ``'utf-8'`` encoding on Windows (instead of
``'mbcs'``) and the ``'surrogateescape'`` error handler on all operating
systems.
Documentation
=============
The documentation continues to be improved.
* A table of quick links has been added to the top of lengthy sections such as
:ref:`built-in-funcs`. In the case of :mod:`itertools`, the links are
accompanied by tables of cheatsheet-style summaries to provide an overview and
memory jog without having to read all of the docs.
* In some cases, the pure Python source code can be a helpful adjunct to the
documentation, so now many modules now feature quick links to the latest
version of the source code. For example, the :mod:`functools` module
documentation has a quick link at the top labeled:
**Source code** :source:`Lib/functools.py`.
(Contributed by Raymond Hettinger; see
`rationale <http://rhettinger.wordpress.com/2011/01/28/open-your-source-more/>`_.)
* The docs now contain more examples and recipes. In particular, :mod:`re`
module has an extensive section, :ref:`re-examples`. Likewise, the
:mod:`itertools` module continues to be updated with new
:ref:`itertools-recipes`.
* The :mod:`datetime` module now has an auxiliary implementation in pure Python.
No functionality was changed. This just provides an easier-to-read alternate
implementation.
(Contributed by Alexander Belopolsky in :issue:`9528`.)
* The unmaintained :file:`Demo` directory has been removed. Some demos were
integrated into the documentation, some were moved to the :file:`Tools/demo`
directory, and others were removed altogether.
(Contributed by Georg Brandl in :issue:`7962`.)
IDLE
====
* The format menu now has an option to clean source files by stripping
trailing whitespace.
(Contributed by Raymond Hettinger; :issue:`5150`.)
* IDLE on Mac OS X now works with both Carbon AquaTk and Cocoa AquaTk.
(Contributed by Kevin Walzer, Ned Deily, and Ronald Oussoren; :issue:`6075`.)
Code Repository
===============
In addition to the existing Subversion code repository at http://svn.python.org
there is now a `Mercurial <http://mercurial.selenic.com/>`_ repository at
http://hg.python.org/\.
After the 3.2 release, there are plans to switch to Mercurial as the primary
repository. This distributed version control system should make it easier for
members of the community to create and share external changesets. See
:pep:`385` for details.
To learn the new version control system, see the `tutorial by Joel
Spolsky <http://hginit.com>`_ or the `Guide to Mercurial Workflows
<http://mercurial.selenic.com/guide/>`_.
Build and C API Changes
=======================
Changes to Python's build process and to the C API include:
* The *idle*, *pydoc* and *2to3* scripts are now installed with a
version-specific suffix on ``make altinstall`` (:issue:`10679`).
* The C functions that access the Unicode Database now accept and return
characters from the full Unicode range, even on narrow unicode builds
(Py_UNICODE_TOLOWER, Py_UNICODE_ISDECIMAL, and others). A visible difference
in Python is that :func:`unicodedata.numeric` now returns the correct value
for large code points, and :func:`repr` may consider more characters as
printable.
(Reported by Bupjoe Lee and fixed by Amaury Forgeot D'Arc; :issue:`5127`.)
* Computed gotos are now enabled by default on supported compilers (which are
detected by the configure script). They can still be disabled selectively by
specifying ``--without-computed-gotos``.
(Contributed by Antoine Pitrou; :issue:`9203`.)
* The option ``--with-wctype-functions`` was removed. The built-in unicode
database is now used for all functions.
(Contributed by Amaury Forgeot D'Arc; :issue:`9210`.)
* Hash values are now values of a new type, :c:type:`Py_hash_t`, which is
defined to be the same size as a pointer. Previously they were of type long,
which on some 64-bit operating systems is still only 32 bits long. As a
result of this fix, :class:`set` and :class:`dict` can now hold more than
``2**32`` entries on builds with 64-bit pointers (previously, they could grow
to that size but their performance degraded catastrophically).
(Suggested by Raymond Hettinger and implemented by Benjamin Peterson;
:issue:`9778`.)
* A new macro :c:macro:`Py_VA_COPY` copies the state of the variable argument
list. It is equivalent to C99 *va_copy* but available on all Python platforms
(:issue:`2443`).
* A new C API function :c:func:`PySys_SetArgvEx` allows an embedded interpreter
to set :attr:`sys.argv` without also modifying :attr:`sys.path`
(:issue:`5753`).
* :c:macro:`PyEval_CallObject` is now only available in macro form. The
function declaration, which was kept for backwards compatibility reasons, is
now removed -- the macro was introduced in 1997 (:issue:`8276`).
* There is a new function :c:func:`PyLong_AsLongLongAndOverflow` which
is analogous to :c:func:`PyLong_AsLongAndOverflow`. They both serve to
convert Python :class:`int` into a native fixed-width type while providing
detection of cases where the conversion won't fit (:issue:`7767`).
* The :c:func:`PyUnicode_CompareWithASCIIString` function now returns *not
equal* if the Python string is *NUL* terminated.
* There is a new function :c:func:`PyErr_NewExceptionWithDoc` that is
like :c:func:`PyErr_NewException` but allows a docstring to be specified.
This lets C exceptions have the same self-documenting capabilities as
their pure Python counterparts (:issue:`7033`).
* When compiled with the ``--with-valgrind`` option, the pymalloc
allocator will be automatically disabled when running under Valgrind. This
gives improved memory leak detection when running under Valgrind, while taking
advantage of pymalloc at other times (:issue:`2422`).
* Removed the ``O?`` format from the *PyArg_Parse* functions. The format is no
longer used and it had never been documented (:issue:`8837`).
There were a number of other small changes to the C-API. See the
:source:`Misc/NEWS` file for a complete list.
Also, there were a number of updates to the Mac OS X build, see
:source:`Mac/BuildScript/README.txt` for details. For users running a 32/64-bit
build, there is a known problem with the default Tcl/Tk on Mac OS X 10.6.
Accordingly, we recommend installing an updated alternative such as
`ActiveState Tcl/Tk 8.5.9 <http://www.activestate.com/activetcl/downloads>`_\.
See http://www.python.org/download/mac/tcltk/ for additional details.
Porting to Python 3.2
=====================
This section lists previously described changes and other bugfixes that may
require changes to your code:
* The :mod:`configparser` module has a number of clean-ups. The major change is
to replace the old :class:`ConfigParser` class with long-standing preferred
alternative :class:`SafeConfigParser`. In addition there are a number of
smaller incompatibilities:
* The interpolation syntax is now validated on
:meth:`~configparser.ConfigParser.get` and
:meth:`~configparser.ConfigParser.set` operations. In the default
interpolation scheme, only two tokens with percent signs are valid: ``%(name)s``
and ``%%``, the latter being an escaped percent sign.
* The :meth:`~configparser.ConfigParser.set` and
:meth:`~configparser.ConfigParser.add_section` methods now verify that
values are actual strings. Formerly, unsupported types could be introduced
unintentionally.
* Duplicate sections or options from a single source now raise either
:exc:`~configparser.DuplicateSectionError` or
:exc:`~configparser.DuplicateOptionError`. Formerly, duplicates would
silently overwrite a previous entry.
* Inline comments are now disabled by default so now the **;** character
can be safely used in values.
* Comments now can be indented. Consequently, for **;** or **#** to appear at
the start of a line in multiline values, it has to be interpolated. This
keeps comment prefix characters in values from being mistaken as comments.
* ``""`` is now a valid value and is no longer automatically converted to an
empty string. For empty strings, use ``"option ="`` in a line.
* The :mod:`nntplib` module was reworked extensively, meaning that its APIs
are often incompatible with the 3.1 APIs.
* :class:`bytearray` objects can no longer be used as filenames; instead,
they should be converted to :class:`bytes`.
* The :meth:`array.tostring` and :meth:`array.fromstring` have been renamed to
:meth:`array.tobytes` and :meth:`array.frombytes` for clarity. The old names
have been deprecated. (See :issue:`8990`.)
* ``PyArg_Parse*()`` functions:
* "t#" format has been removed: use "s#" or "s*" instead
* "w" and "w#" formats has been removed: use "w*" instead
* The :c:type:`PyCObject` type, deprecated in 3.1, has been removed. To wrap
opaque C pointers in Python objects, the :c:type:`PyCapsule` API should be used
instead; the new type has a well-defined interface for passing typing safety
information and a less complicated signature for calling a destructor.
* The :func:`sys.setfilesystemencoding` function was removed because
it had a flawed design.
* The :func:`random.seed` function and method now salt string seeds with an
sha512 hash function. To access the previous version of *seed* in order to
reproduce Python 3.1 sequences, set the *version* argument to *1*,
``random.seed(s, version=1)``.
* The previously deprecated :func:`string.maketrans` function has been removed
in favor of the static methods :meth:`bytes.maketrans` and
:meth:`bytearray.maketrans`. This change solves the confusion around which
types were supported by the :mod:`string` module. Now, :class:`str`,
:class:`bytes`, and :class:`bytearray` each have their own **maketrans** and
**translate** methods with intermediate translation tables of the appropriate
type.
(Contributed by Georg Brandl; :issue:`5675`.)
* The previously deprecated :func:`contextlib.nested` function has been removed
in favor of a plain :keyword:`with` statement which can accept multiple
context managers. The latter technique is faster (because it is built-in),
and it does a better job finalizing multiple context managers when one of them
raises an exception::
with open('mylog.txt') as infile, open('a.out', 'w') as outfile:
for line in infile:
if '<critical>' in line:
outfile.write(line)
(Contributed by Georg Brandl and Mattias Brändström;
`appspot issue 53094 <http://codereview.appspot.com/53094>`_.)
* :func:`struct.pack` now only allows bytes for the ``s`` string pack code.
Formerly, it would accept text arguments and implicitly encode them to bytes
using UTF-8. This was problematic because it made assumptions about the
correct encoding and because a variable-length encoding can fail when writing
to fixed length segment of a structure.
Code such as ``struct.pack('<6sHHBBB', 'GIF87a', x, y)`` should be rewritten
with to use bytes instead of text, ``struct.pack('<6sHHBBB', b'GIF87a', x, y)``.
(Discovered by David Beazley and fixed by Victor Stinner; :issue:`10783`.)
* The :class:`xml.etree.ElementTree` class now raises an
:exc:`xml.etree.ElementTree.ParseError` when a parse fails. Previously it
raised a :exc:`xml.parsers.expat.ExpatError`.
* The new, longer :func:`str` value on floats may break doctests which rely on
the old output format.
* In :class:`subprocess.Popen`, the default value for *close_fds* is now
``True`` under Unix; under Windows, it is ``True`` if the three standard
streams are set to ``None``, ``False`` otherwise. Previously, *close_fds*
was always ``False`` by default, which produced difficult to solve bugs
or race conditions when open file descriptors would leak into the child
process.
* Support for legacy HTTP 0.9 has been removed from :mod:`urllib.request`
and :mod:`http.client`. Such support is still present on the server side
(in :mod:`http.server`).
(Contributed by Antoine Pitrou, :issue:`10711`.)
* SSL sockets in timeout mode now raise :exc:`socket.timeout` when a timeout
occurs, rather than a generic :exc:`~ssl.SSLError`.
(Contributed by Antoine Pitrou, :issue:`10272`.)
* The misleading functions :c:func:`PyEval_AcquireLock()` and
:c:func:`PyEval_ReleaseLock()` have been officially deprecated. The
thread-state aware APIs (such as :c:func:`PyEval_SaveThread()`
and :c:func:`PyEval_RestoreThread()`) should be used instead.
* Due to security risks, :func:`asyncore.handle_accept` has been deprecated, and
a new function, :func:`asyncore.handle_accepted`, was added to replace it.
(Contributed by Giampaolo Rodola in :issue:`6706`.)
* Due to the new :term:`GIL` implementation, :c:func:`PyEval_InitThreads()`
cannot be called before :c:func:`Py_Initialize()` anymore.