This article explains the new features in Python 2.7. The final

release of 2.7 is currently scheduled for June 2010; the detailed

schedule is described in :pep:`373`.

* Float-to-string and string-to-float conversions now round their

results more correctly. And :func:`repr` of a floating-point

number *x* returns a result that's guaranteed to round back to the

same number when converted back to a string.

* The :cfunc:`PyLong_AsLongAndOverflow` C API function.

* Conversions between floating-point numbers and strings are

now correctly rounded on most platforms. These conversions occur

in many different places: :func:`str` on

floats and complex numbers; the :class:`float` and :class:`complex`

constructors;

numeric formatting; serialization and

deserialization of floats and complex numbers using the

:mod:`marshal`, :mod:`pickle`

and :mod:`json` modules;

parsing of float and imaginary literals in Python code;

and :class:`Decimal`-to-float conversion.

Related to this, the :func:`repr` of a floating-point number *x*

now returns a result based on the shortest decimal string that's

guaranteed to round back to *x* under correct rounding (with

round-half-to-even rounding mode). Previously it gave a string

based on rounding x to 17 decimal digits.

The rounding library responsible for this improvement works on

Windows, and on Unix platforms using the gcc, icc, or suncc

compilers. There may be a small number of platforms where correct

operation of this code cannot be guaranteed, so the code is not

used on such systems.

Implemented by Mark Dickinson, using David Gay's :file:`dtoa.c` library;

:issue:`7117`.

The 'F' format code now always formats its output using uppercase characters,

so it will now produce 'INF' and 'NAN'.

(Contributed by Eric Smith; :issue:`3382`.)

Integer division is also more accurate in its rounding behaviours. (Also

implemented by Mark Dickinson; :issue:`1811`.)

* The :class:`file` object will now set the :attr:`filename` attribute

on the :exc:`IOError` exception when trying to open a directory

on POSIX platforms. (Noted by Jan Kaliszewski; :issue:`4764`.)

* Extra parentheses in function definitions are illegal in Python 3.x,

meaning that you get a syntax error from ``def f((x)): pass``. In

Python3-warning mode, Python 2.7 will now warn about this odd usage.

(Noted by James Lingard; :issue:`7362`.)

* The garbage collector now performs better for one common usage

pattern: when many objects are being allocated without deallocating

any of them. This would previously take quadratic

time for garbage collection, but now the number of full garbage collections

is reduced as the number of objects on the heap grows.

The new logic is to only perform a full garbage collection pass when

the middle generation has been collected 10 times and when the

number of survivor objects from the middle generation exceeds 10% of

the number of objects in the oldest generation. (Suggested by Martin

von Loewis and implemented by Antoine Pitrou; :issue:`4074`.)

read-only :attr:`maxlen` attribute, and has a

:meth:`reverse` method that reverses the elements of the deque in-place.

(Added by Raymond Hettinger.)

* The :mod:`copy` module's :func:`deepcopy` function will now

correctly copy bound instance methods. (Implemented by

Robert Collins; :issue:`1515`.)

* New method: the :mod:`datetime` module's :class:`timedelta` class

gained a :meth:`total_seconds` method that returns the number of seconds

in the duration. (Contributed by Brian Quinlan; :issue:`5788`.)

The :class:`distutils.dist.DistributionMetadata` class'

:meth:`read_pkg_file` method will read the contents of a package's

:file:`PKG-INFO` metadata file. For an example of its use,

XXX link to file:///MacDev/svn.python.org/python-trunk/Doc/build/html/distutils/examples.html#reading-the-metadata

(Contributed by Tarek Ziade; :issue:`7457`.)

* The :mod:`ftplib` module gained the ability to establish secure FTP

connections using TLS encapsulation of authentication as well as

subsequent control and data transfers. This is provided by the new

:class:`ftplib.FTP_TLS` class.

(Contributed by Giampaolo Rodola', :issue:`2054`.) The :meth:`storbinary`

method for binary uploads can now restart uploads thanks to an added

*rest* parameter (patch by Pablo Mouzo; :issue:`6845`.)

* New functions: the :mod:`math` module gained

:func:`erf` and :func:`erfc` for the error function and the complementary error function,

:func:`expm1` which computes ``e**x - 1`` with more precision than

using :func:`exp` and subtracting 1,

:func:`gamma` for the Gamma function, and

:func:`lgamma` for the natural log of the Gamma function.

* New functions: the :mod:`os` module wraps the following POSIX system

calls: :func:`getresgid` and :func:`getresuid`, which return the

real, effective, and saved GIDs and UIDs;

:func:`setresgid` and :func:`setresuid`, which set

real, effective, and saved GIDs and UIDs to new values;

:func:`initgroups`. (GID/UID functions

contributed by Travis H.; :issue:`6508`. Support for initgroups added

by Jean-Paul Calderone; :issue:`7333`.)

to users who wish to write new importers that can participate in the

* New function: :cfunc:`PyErr_NewExceptionWithDoc` creates a new

exception class, just as the existing :cfunc:`PyErr_NewException` does,

but takes an extra ``char *`` argument containing the docstring for the

new exception class. (Added by the 'lekma' user on the Python bug tracker;

:issue:`7033`.)

* New function: :cfunc:`PyLong_AsLongAndOverflow` approximates a Python long

integer as a C :ctype:`long`. If the number is too large to fit into

a :ctype:`long`, an *overflow* flag is set and returned to the caller.

(Contributed by Case Van Horsen; :issue:`7528`.)

* New format codes: the :cfunc:`PyFormat_FromString`,

:cfunc:`PyFormat_FromStringV`, and :cfunc:`PyErr_Format` now

accepts ``%lld`` and ``%llu`` format codes for displaying values of

C's :ctype:`long long` types.

(Contributed by Mark Dickinson; :issue:`7228`.)

* Compiling Python with the :option:`--with-valgrind` option will now

disable the pymalloc allocator, which is difficult for the Valgrind to

analyze correctly. Valgrind will therefore be better at detecting

memory leaks and overruns. (Contributed by James Henstridge; :issue:`2422`.)

* The :mod:`mimelib` module will now read the MIME database from

the Windows registry when initializing.

(Patch by Gabriel Genellina; :issue:`4969`.)

* The :meth:`readline` method of :class:`StringIO` objects now does

nothing when a negative length is requested, as other file-like

objects do. (:issue:`7348`).