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Ezio Melotti 2010-04-20 09:55:05 +00:00
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282
Doc/whatsnew/2.7.rst
View File

@ -8,7 +8,7 @@
.. Fix accents on Kristjan Valur Jonsson, Fuerstenau
.. Big jobs: argparse, ElementTree 1.3, pep 391, 3106, sysconfig
.. Big jobs: ElementTree 1.3, pep 391, sysconfig
.. unittest test discovery
.. hyperlink all the methods & functions.
@ -58,8 +58,9 @@ release of 2.7 is currently scheduled for June 2010; the detailed
schedule is described in :pep:`373`.
Python 2.7 is planned to be the last major release in the 2.x series.
Though more major releases have not been absolutely ruled out, it's
likely that the 2.7 release will have an extended period of
Though more major releases have not been absolutely ruled out, the
Python maintainers are planning to focus more on Python 3.x. Despite
that, it's likely that the 2.7 release will have a longer period of
maintenance compared to earlier 2.x versions.
.. Compare with previous release in 2 - 3 sentences here.
@ -181,14 +182,21 @@ remains O(1).
.. :meth:`~collections.namedtuple._asdict()` (see below)
The standard library now supports use of ordered dictionaries in several
modules. The :mod:`configparser` module uses them by default. This lets
configuration files be read, modified, and then written back in their original
order. The :meth:`~collections.somenamedtuple._asdict()` method for
:func:`collections.namedtuple` now returns an ordered dictionary with the
values appearing in the same order as the underlying tuple indices.
The :mod:`json` module is being built-out with an *object_pairs_hook* to allow
OrderedDicts to be built by the decoder.
Support was also added for third-party tools like `PyYAML <http://pyyaml.org/>`_.
modules.
* The :mod:`ConfigParser` module uses them by default, letting
configuration files be read, modified, and then written back in their original
order.
* The :meth:`~collections.somenamedtuple._asdict()` method for
:func:`collections.namedtuple` now returns an ordered dictionary with the
values appearing in the same order as the underlying tuple indices.
* The :mod:`json` module's :class:`~json.JSONDecoder` class
constructor was extended with an *object_pairs_hook* parameter to
allow :class:`OrderedDict` instances to be built by the decoder.
Support was also added for third-party tools like
`PyYAML <http://pyyaml.org/>`_.
.. seealso::
@ -254,11 +262,69 @@ automated way to update these scripts. (Making the :mod:`argparse`
API consistent with :mod:`optparse`'s interface was discussed but
rejected as too messy and difficult.)
To summarize, if you're writing a new script and don't need to worry
In short, if you're writing a new script and don't need to worry
about compatibility with earlier versions of Python, use
:mod:`argparse` instead of :mod:`optparse`.
XXX need an example
Here's an example::
import argparse
parser = argparse.ArgumentParser(description='Command-line example.')
# Add optional switches
parser.add_argument('-v', action='store_true', dest='is_verbose',
help='produce verbose output')
parser.add_argument('-o', action='store', dest='output',
metavar='FILE',
help='direct output to FILE instead of stdout')
parser.add_argument('-C', action='store', type=int, dest='context',
metavar='NUM', default=0,
help='display NUM lines of added context')
# Allow any number of additional arguments.
parser.add_argument(nargs='*', action='store', dest='inputs',
help='input filenames (default is stdin)')
args = parser.parse_args()
print args.__dict__
Unless you override it, :option:`-h` and :option:`--help` switches
are automatically added, and produce neatly formatted output::
-> ./python.exe argparse-example.py --help
usage: argparse-example.py [-h] [-v] [-o FILE] [-C NUM] [inputs [inputs ...]]
Command-line example.
positional arguments:
inputs input filenames (default is stdin)
optional arguments:
-h, --help show this help message and exit
-v produce verbose output
-o FILE direct output to FILE instead of stdout
-C NUM display NUM lines of added context
Similarly to :mod:`optparse`, the command-line switches and arguments
are returned as an object with attributes named by the *dest* parameters::
-> ./python.exe argparse-example.py -v
{'output': None, 'is_verbose': True, 'context': 0, 'inputs': []}
-> ./python.exe argparse-example.py -v -o /tmp/output -C 4 file1 file2
{'output': '/tmp/output', 'is_verbose': True, 'context': 4,
'inputs': ['file1', 'file2']}
:mod:`argparse` has much fancier validation than :mod:`optparse`; you
can specify an exact number of arguments as an integer, 0 or more
arguments by passing ``'*'``, 1 or more by passing ``'+'``, or an
optional argument with ``'?'``. A top-level parser can contain
sub-parsers, so you can define subcommands that have different sets of
switches, as in ``svn commit``, ``svn checkout``, etc. You can
specify an argument type as :class:`~argparse.FileType`, which will
automatically open files for you and understands that ``'-'`` means
standard input or output.
.. seealso::
@ -272,7 +338,28 @@ XXX need an example
PEP 391: Dictionary-Based Configuration For Logging
====================================================
XXX write this section.
.. not documented in library reference yet.
The :mod:`logging` module is very flexible; an application can define
a tree of logging subsystems, and each logger in this tree can filter
out certain messages, format them differently, and direct messages to
a varying number of handlers.
All this flexibility can require a lot of configuration. You can
write Python statements to create objects and set their properties,
but a complex set-up would require verbose but boring code.
:mod:`logging` also supports a :func:`~logging.config.fileConfig`
function that parses a file, but the file format doesn't support
configuring filters, and it's messier to generate programmatically.
Python 2.7 adds a :func:`~logging.config.dictConfig` function that
uses a dictionary, and there are many ways to produce a dictionary
from different sources. You can construct one with code, of course.
Python's standard library now includes a JSON parser, so you could
parse a file containing JSON, or you could use a YAML parsing library
if one is installed.
XXX describe an example.
Two smaller enhancements to the logging module are:
@ -296,7 +383,48 @@ Two smaller enhancements to the logging module are:
PEP 3106: Dictionary Views
====================================================
XXX write this section.
The dictionary methods :meth:`keys`, :meth:`values`, and :meth:`items`
are different in Python 3.x. They return an object called a :dfn:`view`
instead of a fully materialized list.
.. Views can be iterated over, but they also behave like sets. XXX not working.
It's not possible to change the return values of :meth:`keys`,
:meth:`values`, and :meth:`items` in Python 2.7 because too much code
would break. Instead the 3.x versions were added under the new names
of :meth:`viewkeys`, :meth:`viewvalues`, and :meth:`viewitems`.
::
>>> d = dict((i*10, chr(65+i)) for i in range(26))
>>> d
{0: 'A', 130: 'N', 10: 'B', 140: 'O', 20: ..., 250: 'Z'}
>>> d.viewkeys()
dict_keys([0, 130, 10, 140, 20, 150, 30, ..., 250])
The view keeps track of the dictionary and its contents change as the
dictionary is modified::
>>> vk = d.viewkeys()
>>> vk
dict_keys([0, 130, 10, ..., 250])
>>> d[260] = '&'
>>> vk
dict_keys([0, 130, 260, 10, ..., 250])
However, note that you can't add or remove keys while you're iterating
over the view::
>>> for k in vk:
... d[k*2] = k
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RuntimeError: dictionary changed size during iteration
You can use the view methods in Python 2.x code, and the 2to3
converter will change them to the standard :meth:`keys`,
:meth:`values`, and :meth:`items` methods.
.. seealso::
@ -496,6 +624,10 @@ Some smaller changes made to the core Python language are:
Python3-warning mode, Python 2.7 will now warn about this odd usage.
(Noted by James Lingard; :issue:`7362`.)
* It's now possible to create weak references to old-style class
objects. New-style classes were always weak-referenceable. (Fixed
by Antoine Pitrou; :issue:`8268`.)
* When a module object is garbage-collected, the module's dictionary is
now only cleared if no one else is holding a reference to the
dictionary (:issue:`7140`).
@ -684,11 +816,15 @@ changes, or look through the Subversion logs for all the details.
>>> c['z']
0
There are two additional :class:`~collections.Counter` methods:
:meth:`~collections.Counter.most_common` returns the N most common elements
and their counts, and :meth:`~collections.Counter.elements`
returns an iterator over the contained element, repeating each element
as many times as its count::
There are three additional :class:`~collections.Counter` methods:
:meth:`~collections.Counter.most_common` returns the N most common
elements and their counts. :meth:`~collections.Counter.elements`
returns an iterator over the contained elements, repeating each
element as many times as its count.
:meth:`~collections.Counter.subtract` takes an iterable and
subtracts one for each element instead of adding; if the argument is
a dictionary or another :class:`Counter`, the counts are
subtracted. ::
>>> c.most_common(5)
[(' ', 6), ('e', 5), ('s', 3), ('a', 2), ('i', 2)]
@ -697,11 +833,16 @@ changes, or look through the Subversion logs for all the details.
'e', 'e', 'e', 'e', 'e', 'g', 'f', 'i', 'i',
'h', 'h', 'm', 'l', 'l', 'o', 'n', 'p', 's',
's', 's', 'r', 't', 't', 'x'
.. maybe it's better to use list(c.elements()) here
>>> c['e']
5
>>> c.subtract('very heavy on the letter e')
>>> c['e'] # Count is now lower
-1
Contributed by Raymond Hettinger; :issue:`1696199`.
.. revision 79660
The new :class:`~collections.OrderedDict` class is described in the earlier
section :ref:`pep-0372`.
@ -757,18 +898,28 @@ changes, or look through the Subversion logs for all the details.
:meth:`~decimal.Context.canonical` and :meth:`~decimal.Context.is_canonical`
methods. (Patch by Juan José Conti; :issue:`7633`.)
The constructor for :class:`~decimal.Decimal` now accepts non-European
Unicode characters, such as Arabic-Indic digits. (Contributed by
Mark Dickinson; :issue:`6595`.)
The constructor for :class:`~decimal.Decimal` now accepts
floating-point numbers (added by Raymond Hettinger; :issue:`8257`)
and non-European Unicode characters such as Arabic-Indic digits
(contributed by Mark Dickinson; :issue:`6595`).
When using :class:`~decimal.Decimal` instances with a string's
:meth:`~str.format` method, the default alignment was previously
left-alignment. This has been changed to right-alignment, which seems
more sensible for numeric types. (Changed by Mark Dickinson; :issue:`6857`.)
* The :class:`~fractions.Fraction` class now accepts two rational numbers
as arguments to its constructor.
(Implemented by Mark Dickinson; :issue:`5812`.)
* The :mod:`difflib` module now produces output that is more
compatible with modern :command:`diff`/:command:`patch` tools thanks
to two changes: 1) the header giving the filename now uses a tab
character instead of spaces as a separator, and 2) the date format
used is now ISO-8601 style, ``2005-01-26 23:30:50``. (Fixed by
Anatoly Techtonik; :issue:`7585`.)
* The :class:`~fractions.Fraction` class now accepts a single float or
:class:`~decimal.Decimal` instance, or two rational numbers, as
arguments to its constructor. (Implemented by Mark Dickinson;
rationals added in :issue:`5812`, and float/decimal in
:issue:`8294`.)
An oversight was fixed, making the :class:`Fraction` match the other
numeric types; ordering comparisons (``<``, ``<=``, ``>``, ``>=``) between
@ -837,6 +988,25 @@ changes, or look through the Subversion logs for all the details.
* The :mod:`imaplib` module now supports IPv6 addresses.
(Contributed by Derek Morr; :issue:`1655`.)
* New function: the :mod:`inspect` module's :func:`~inspect.getcallargs`
takes a callable and its positional and keyword arguments,
and figures out which of the callable's parameters will receive each argument,
returning a dictionary mapping argument names to their values. For example::
>>> from inspect import getcallargs
>>> def f(a, b=1, *pos, **named):
... pass
>>> getcallargs(f, 1, 2, 3)
{'a': 1, 'named': {}, 'b': 2, 'pos': (3,)}
>>> getcallargs(f, a=2, x=4)
{'a': 2, 'named': {'x': 4}, 'b': 1, 'pos': ()}
>>> getcallargs(f)
Traceback (most recent call last):
...
TypeError: f() takes at least 1 argument (0 given)
Contributed by George Sakkis; :issue:`3135`.
* Updated module: The :mod:`io` library has been upgraded to the version shipped with
Python 3.1. For 3.1, the I/O library was entirely rewritten in C
and is 2 to 20 times faster depending on the task being performed. The
@ -975,13 +1145,17 @@ changes, or look through the Subversion logs for all the details.
Victor Stinner; :issue:`3137`.)
* The :mod:`socket` module's :class:`~ssl.SSL` objects now support the
buffer API, which fixed a test suite failure. (Fixed by Antoine
Pitrou; :issue:`7133`.) The version of OpenSSL being used is
now available as the module attributes
:attr:`OPENSSL_VERSION` (a string),
buffer API, which fixed a test suite failure (fix by Antoine Pitrou;
:issue:`7133`). :class:`SSL` objects also now automatically set
OpenSSL's :cmacro:`SSL_MODE_AUTO_RETRY`, which will prevent an error
code being returned from :meth:`recv` operations that trigger an SSL
renegotiation (fix by Antoine Pitrou; :issue:`8222`).
The version of OpenSSL being used is now available as the module
attributes :attr:`OPENSSL_VERSION` (a string),
:attr:`OPENSSL_VERSION_INFO` (a 5-tuple), and
:attr:`OPENSSL_VERSION_NUMBER` (an integer). (Added by Antoine Pitrou;
:issue:`8321`.)
:attr:`OPENSSL_VERSION_NUMBER` (an integer). (Added by Antoine
Pitrou; :issue:`8321`.)
The :func:`~socket.create_connection` function
gained a *source_address* parameter, a ``(host, port)`` 2-tuple
@ -1011,7 +1185,10 @@ changes, or look through the Subversion logs for all the details.
errors when a value is too large for a particular integer format
code (one of ``bBhHiIlLqQ``); it now always raises a
:exc:`struct.error` exception. (Changed by Mark Dickinson;
:issue:`1523`.)
:issue:`1523`.) The :func:`~struct.pack` function will also
attempt to use :meth:`__index__` to convert and pack non-integers
before trying the :meth:`__int__` method or reporting an error.
(Changed by Mark Dickinson; :issue:`8300`.)
* New function: the :mod:`subprocess` module's
:func:`~subprocess.check_output` runs a command with a specified set of arguments
@ -1346,6 +1523,18 @@ Build and C API Changes
Changes to Python's build process and to the C API include:
* The latest release of the GNU Debugger, GDB 7, can be `scripted
using Python
<http://sourceware.org/gdb/current/onlinedocs/gdb/Python.html>`__.
When you begin debugging an executable program P, GDB will look for
a file named ``P-gdb.py`` and automatically read it. Dave Malcolm
contributed a :file:`python-gdb.py` that adds a number of useful
commands when debugging Python itself. For example, there are
``py-up`` and ``py-down`` that go up or down one Python stack frame,
which usually corresponds to several C stack frames. ``py-print``
prints the value of a Python variable, and ``py-bt`` prints the
Python stack trace. (Added as a result of :issue:`8032`.)
* If you use the :file:`.gdbinit` file provided with Python,
the "pyo" macro in the 2.7 version now works correctly when the thread being
debugged doesn't hold the GIL; the macro now acquires it before printing.
@ -1442,9 +1631,10 @@ Changes to Python's build process and to the C API include:
building the :mod:`pyexpat` module to use the system Expat library.
(Contributed by Arfrever Frehtes Taifersar Arahesis; :issue:`7609`.)
* New configure option: Compiling Python with the
* New configure option: compiling Python with the
:option:`--with-valgrind` option will now disable the pymalloc
allocator, which is difficult for the Valgrind to analyze correctly.
allocator, which is difficult for the Valgrind memory-error detector
to analyze correctly.
Valgrind will therefore be better at detecting memory leaks and
overruns. (Contributed by James Henstridge; :issue:`2422`.)
@ -1459,6 +1649,10 @@ Changes to Python's build process and to the C API include:
but it's available if anyone wishes to use it.
(Added by Mark Dickinson; :issue:`2937`.)
:program:`configure` also now sets a :envvar:`LDCXXSHARED` Makefile
variable for supporting C++ linking. (Contributed by Arfrever
Frehtes Taifersar Arahesis; :issue:`1222585`.)
* The build process now creates the necessary files for pkg-config
support. (Contributed by Clinton Roy; :issue:`3585`.)
@ -1482,6 +1676,13 @@ Port-Specific Changes: Windows
the native thread-local storage functions are now used.
(Contributed by Kristjan Valur Jonsson; :issue:`3582`.)
* The :func:`os.kill` function now works on Windows. The signal value
can be the constants :const:`CTRL_C_EVENT`,
:const:`CTRL_BREAK_EVENT`, or any integer. The Control-C and
Control-Break keystroke events can be sent to subprocesses; any
other value will use the :cfunc:`TerminateProcess` API.
(Contributed by Miki Tebeka; :issue:`1220212`.)
* The :func:`os.listdir` function now correctly fails
for an empty path. (Fixed by Hirokazu Yamamoto; :issue:`5913`.)
@ -1533,6 +1734,11 @@ Other Changes and Fixes
with a new :option:`-F` switch that runs selected tests in a loop
until they fail. (Added by Antoine Pitrou; :issue:`7312`.)
* When executed as a script, the :file:`py_compile.py` module now
accepts ``'-'`` as an argument, which will read standard input for
the list of filenames to be compiled. (Contributed by Piotr
Ożarowski; :issue:`8233`.)
.. ======================================================================
Porting to Python 2.7
@ -1591,5 +1797,5 @@ Acknowledgements
The author would like to thank the following people for offering
suggestions, corrections and assistance with various drafts of this
article: Ryan Lovett, Hugh Secker-Walker.
article: Ryan Lovett, R. David Murray, Hugh Secker-Walker.