mirror of https://github.com/python/cpython
1207 lines
58 KiB
ReStructuredText
1207 lines
58 KiB
ReStructuredText
****************************
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What's New in Python 2.0
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****************************
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:Author: A.M. Kuchling and Moshe Zadka
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.. |release| replace:: 1.02
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.. $Id: whatsnew20.tex 50964 2006-07-30 03:03:43Z fred.drake $
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Introduction
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============
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A new release of Python, version 2.0, was released on October 16, 2000. This
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article covers the exciting new features in 2.0, highlights some other useful
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changes, and points out a few incompatible changes that may require rewriting
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code.
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Python's development never completely stops between releases, and a steady flow
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of bug fixes and improvements are always being submitted. A host of minor fixes,
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a few optimizations, additional docstrings, and better error messages went into
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2.0; to list them all would be impossible, but they're certainly significant.
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Consult the publicly available CVS logs if you want to see the full list. This
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progress is due to the five developers working for PythonLabs are now getting
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paid to spend their days fixing bugs, and also due to the improved communication
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resulting from moving to SourceForge.
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.. ======================================================================
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What About Python 1.6?
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======================
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Python 1.6 can be thought of as the Contractual Obligations Python release.
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After the core development team left CNRI in May 2000, CNRI requested that a 1.6
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release be created, containing all the work on Python that had been performed at
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CNRI. Python 1.6 therefore represents the state of the CVS tree as of May 2000,
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with the most significant new feature being Unicode support. Development
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continued after May, of course, so the 1.6 tree received a few fixes to ensure
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that it's forward-compatible with Python 2.0. 1.6 is therefore part of Python's
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evolution, and not a side branch.
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So, should you take much interest in Python 1.6? Probably not. The 1.6final
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and 2.0beta1 releases were made on the same day (September 5, 2000), the plan
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being to finalize Python 2.0 within a month or so. If you have applications to
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maintain, there seems little point in breaking things by moving to 1.6, fixing
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them, and then having another round of breakage within a month by moving to 2.0;
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you're better off just going straight to 2.0. Most of the really interesting
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features described in this document are only in 2.0, because a lot of work was
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done between May and September.
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.. ======================================================================
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New Development Process
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=======================
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The most important change in Python 2.0 may not be to the code at all, but to
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how Python is developed: in May 2000 the Python developers began using the tools
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made available by SourceForge for storing source code, tracking bug reports,
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and managing the queue of patch submissions. To report bugs or submit patches
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for Python 2.0, use the bug tracking and patch manager tools available from
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Python's project page, located at https://sourceforge.net/projects/python/.
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The most important of the services now hosted at SourceForge is the Python CVS
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tree, the version-controlled repository containing the source code for Python.
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Previously, there were roughly 7 or so people who had write access to the CVS
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tree, and all patches had to be inspected and checked in by one of the people on
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this short list. Obviously, this wasn't very scalable. By moving the CVS tree
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to SourceForge, it became possible to grant write access to more people; as of
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September 2000 there were 27 people able to check in changes, a fourfold
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increase. This makes possible large-scale changes that wouldn't be attempted if
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they'd have to be filtered through the small group of core developers. For
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example, one day Peter Schneider-Kamp took it into his head to drop K&R C
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compatibility and convert the C source for Python to ANSI C. After getting
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approval on the python-dev mailing list, he launched into a flurry of checkins
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that lasted about a week, other developers joined in to help, and the job was
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done. If there were only 5 people with write access, probably that task would
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have been viewed as "nice, but not worth the time and effort needed" and it
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would never have gotten done.
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The shift to using SourceForge's services has resulted in a remarkable increase
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in the speed of development. Patches now get submitted, commented on, revised
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by people other than the original submitter, and bounced back and forth between
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people until the patch is deemed worth checking in. Bugs are tracked in one
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central location and can be assigned to a specific person for fixing, and we can
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count the number of open bugs to measure progress. This didn't come without a
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cost: developers now have more e-mail to deal with, more mailing lists to
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follow, and special tools had to be written for the new environment. For
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example, SourceForge sends default patch and bug notification e-mail messages
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that are completely unhelpful, so Ka-Ping Yee wrote an HTML screen-scraper that
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sends more useful messages.
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The ease of adding code caused a few initial growing pains, such as code was
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checked in before it was ready or without getting clear agreement from the
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developer group. The approval process that has emerged is somewhat similar to
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that used by the Apache group. Developers can vote +1, +0, -0, or -1 on a patch;
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+1 and -1 denote acceptance or rejection, while +0 and -0 mean the developer is
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mostly indifferent to the change, though with a slight positive or negative
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slant. The most significant change from the Apache model is that the voting is
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essentially advisory, letting Guido van Rossum, who has Benevolent Dictator For
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Life status, know what the general opinion is. He can still ignore the result of
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a vote, and approve or reject a change even if the community disagrees with him.
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Producing an actual patch is the last step in adding a new feature, and is
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usually easy compared to the earlier task of coming up with a good design.
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Discussions of new features can often explode into lengthy mailing list threads,
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making the discussion hard to follow, and no one can read every posting to
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python-dev. Therefore, a relatively formal process has been set up to write
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Python Enhancement Proposals (PEPs), modelled on the internet RFC process. PEPs
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are draft documents that describe a proposed new feature, and are continually
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revised until the community reaches a consensus, either accepting or rejecting
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the proposal. Quoting from the introduction to :pep:`1`, "PEP Purpose and
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Guidelines":
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.. epigraph::
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PEP stands for Python Enhancement Proposal. A PEP is a design document
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providing information to the Python community, or describing a new feature for
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Python. The PEP should provide a concise technical specification of the feature
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and a rationale for the feature.
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We intend PEPs to be the primary mechanisms for proposing new features, for
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collecting community input on an issue, and for documenting the design decisions
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that have gone into Python. The PEP author is responsible for building
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consensus within the community and documenting dissenting opinions.
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Read the rest of :pep:`1` for the details of the PEP editorial process, style, and
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format. PEPs are kept in the Python CVS tree on SourceForge, though they're not
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part of the Python 2.0 distribution, and are also available in HTML form from
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https://peps.python.org/. As of September 2000, there are 25 PEPs, ranging
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from :pep:`201`, "Lockstep Iteration", to PEP 225, "Elementwise/Objectwise
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Operators".
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.. ======================================================================
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Unicode
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=======
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The largest new feature in Python 2.0 is a new fundamental data type: Unicode
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strings. Unicode uses 16-bit numbers to represent characters instead of the
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8-bit number used by ASCII, meaning that 65,536 distinct characters can be
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supported.
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The final interface for Unicode support was arrived at through countless
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often-stormy discussions on the python-dev mailing list, and mostly implemented by
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Marc-André Lemburg, based on a Unicode string type implementation by Fredrik
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Lundh. A detailed explanation of the interface was written up as :pep:`100`,
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"Python Unicode Integration". This article will simply cover the most
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significant points about the Unicode interfaces.
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In Python source code, Unicode strings are written as ``u"string"``. Arbitrary
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Unicode characters can be written using a new escape sequence, :samp:`\\u{HHHH}`, where
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*HHHH* is a 4-digit hexadecimal number from 0000 to FFFF. The existing
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:samp:`\\x{HH}` escape sequence can also be used, and octal escapes can be used for
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characters up to U+01FF, which is represented by ``\777``.
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Unicode strings, just like regular strings, are an immutable sequence type.
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They can be indexed and sliced, but not modified in place. Unicode strings have
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an ``encode( [encoding] )`` method that returns an 8-bit string in the desired
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encoding. Encodings are named by strings, such as ``'ascii'``, ``'utf-8'``,
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``'iso-8859-1'``, or whatever. A codec API is defined for implementing and
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registering new encodings that are then available throughout a Python program.
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If an encoding isn't specified, the default encoding is usually 7-bit ASCII,
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though it can be changed for your Python installation by calling the
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``sys.setdefaultencoding(encoding)`` function in a customized version of
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:file:`site.py`.
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Combining 8-bit and Unicode strings always coerces to Unicode, using the default
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ASCII encoding; the result of ``'a' + u'bc'`` is ``u'abc'``.
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New built-in functions have been added, and existing built-ins modified to
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support Unicode:
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* ``unichr(ch)`` returns a Unicode string 1 character long, containing the
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character *ch*.
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* ``ord(u)``, where *u* is a 1-character regular or Unicode string, returns the
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number of the character as an integer.
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* ``unicode(string [, encoding] [, errors] )`` creates a Unicode string
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from an 8-bit string. ``encoding`` is a string naming the encoding to use. The
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``errors`` parameter specifies the treatment of characters that are invalid for
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the current encoding; passing ``'strict'`` as the value causes an exception to
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be raised on any encoding error, while ``'ignore'`` causes errors to be silently
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ignored and ``'replace'`` uses U+FFFD, the official replacement character, in
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case of any problems.
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* The ``exec`` statement, and various built-ins such as ``eval()``,
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``getattr()``, and ``setattr()`` will also accept Unicode strings as well as
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regular strings. (It's possible that the process of fixing this missed some
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built-ins; if you find a built-in function that accepts strings but doesn't
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accept Unicode strings at all, please report it as a bug.)
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A new module, :mod:`unicodedata`, provides an interface to Unicode character
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properties. For example, ``unicodedata.category(u'A')`` returns the 2-character
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string 'Lu', the 'L' denoting it's a letter, and 'u' meaning that it's
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uppercase. ``unicodedata.bidirectional(u'\u0660')`` returns 'AN', meaning that
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U+0660 is an Arabic number.
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The :mod:`codecs` module contains functions to look up existing encodings and
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register new ones. Unless you want to implement a new encoding, you'll most
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often use the ``codecs.lookup(encoding)`` function, which returns a
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4-element tuple: ``(encode_func, decode_func, stream_reader, stream_writer)``.
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* *encode_func* is a function that takes a Unicode string, and returns a 2-tuple
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``(string, length)``. *string* is an 8-bit string containing a portion (perhaps
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all) of the Unicode string converted into the given encoding, and *length* tells
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you how much of the Unicode string was converted.
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* *decode_func* is the opposite of *encode_func*, taking an 8-bit string and
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returning a 2-tuple ``(ustring, length)``, consisting of the resulting Unicode
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string *ustring* and the integer *length* telling how much of the 8-bit string
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was consumed.
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* *stream_reader* is a class that supports decoding input from a stream.
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*stream_reader(file_obj)* returns an object that supports the :meth:`!read`,
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:meth:`!readline`, and :meth:`!readlines` methods. These methods will all
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translate from the given encoding and return Unicode strings.
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* *stream_writer*, similarly, is a class that supports encoding output to a
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stream. *stream_writer(file_obj)* returns an object that supports the
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:meth:`!write` and :meth:`!writelines` methods. These methods expect Unicode
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strings, translating them to the given encoding on output.
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For example, the following code writes a Unicode string into a file, encoding
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it as UTF-8::
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import codecs
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unistr = u'\u0660\u2000ab ...'
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(UTF8_encode, UTF8_decode,
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UTF8_streamreader, UTF8_streamwriter) = codecs.lookup('UTF-8')
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output = UTF8_streamwriter( open( '/tmp/output', 'wb') )
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output.write( unistr )
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output.close()
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The following code would then read UTF-8 input from the file::
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input = UTF8_streamreader( open( '/tmp/output', 'rb') )
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print repr(input.read())
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input.close()
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Unicode-aware regular expressions are available through the :mod:`re` module,
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which has a new underlying implementation called SRE written by Fredrik Lundh of
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Secret Labs AB.
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A ``-U`` command line option was added which causes the Python compiler to
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interpret all string literals as Unicode string literals. This is intended to be
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used in testing and future-proofing your Python code, since some future version
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of Python may drop support for 8-bit strings and provide only Unicode strings.
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.. ======================================================================
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List Comprehensions
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===================
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Lists are a workhorse data type in Python, and many programs manipulate a list
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at some point. Two common operations on lists are to loop over them, and either
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pick out the elements that meet a certain criterion, or apply some function to
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each element. For example, given a list of strings, you might want to pull out
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all the strings containing a given substring, or strip off trailing whitespace
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from each line.
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The existing :func:`map` and :func:`filter` functions can be used for this
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purpose, but they require a function as one of their arguments. This is fine if
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there's an existing built-in function that can be passed directly, but if there
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isn't, you have to create a little function to do the required work, and
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Python's scoping rules make the result ugly if the little function needs
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additional information. Take the first example in the previous paragraph,
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finding all the strings in the list containing a given substring. You could
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write the following to do it::
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# Given the list L, make a list of all strings
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# containing the substring S.
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sublist = filter( lambda s, substring=S:
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string.find(s, substring) != -1,
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L)
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Because of Python's scoping rules, a default argument is used so that the
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anonymous function created by the :keyword:`lambda` expression knows what
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substring is being searched for. List comprehensions make this cleaner::
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sublist = [ s for s in L if string.find(s, S) != -1 ]
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List comprehensions have the form::
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[ expression for expr in sequence1
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for expr2 in sequence2 ...
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for exprN in sequenceN
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if condition ]
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The :keyword:`!for`...\ :keyword:`!in` clauses contain the sequences to be
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iterated over. The sequences do not have to be the same length, because they
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are *not* iterated over in parallel, but from left to right; this is explained
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more clearly in the following paragraphs. The elements of the generated list
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will be the successive values of *expression*. The final :keyword:`!if` clause
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is optional; if present, *expression* is only evaluated and added to the result
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if *condition* is true.
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To make the semantics very clear, a list comprehension is equivalent to the
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following Python code::
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for expr1 in sequence1:
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for expr2 in sequence2:
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...
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for exprN in sequenceN:
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if (condition):
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# Append the value of
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# the expression to the
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# resulting list.
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This means that when there are multiple :keyword:`!for`...\ :keyword:`!in`
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clauses, the resulting list will be equal to the product of the lengths of all
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the sequences. If you have two lists of length 3, the output list is 9 elements
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long::
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seq1 = 'abc'
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seq2 = (1,2,3)
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>>> [ (x,y) for x in seq1 for y in seq2]
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[('a', 1), ('a', 2), ('a', 3), ('b', 1), ('b', 2), ('b', 3), ('c', 1),
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('c', 2), ('c', 3)]
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To avoid introducing an ambiguity into Python's grammar, if *expression* is
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creating a tuple, it must be surrounded with parentheses. The first list
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comprehension below is a syntax error, while the second one is correct::
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# Syntax error
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[ x,y for x in seq1 for y in seq2]
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# Correct
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[ (x,y) for x in seq1 for y in seq2]
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The idea of list comprehensions originally comes from the functional programming
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language Haskell (https://www.haskell.org). Greg Ewing argued most effectively
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for adding them to Python and wrote the initial list comprehension patch, which
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was then discussed for a seemingly endless time on the python-dev mailing list
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and kept up-to-date by Skip Montanaro.
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.. ======================================================================
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Augmented Assignment
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====================
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Augmented assignment operators, another long-requested feature, have been added
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to Python 2.0. Augmented assignment operators include ``+=``, ``-=``, ``*=``,
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and so forth. For example, the statement ``a += 2`` increments the value of the
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variable ``a`` by 2, equivalent to the slightly lengthier ``a = a + 2``.
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The full list of supported assignment operators is ``+=``, ``-=``, ``*=``,
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``/=``, ``%=``, ``**=``, ``&=``, ``|=``, ``^=``, ``>>=``, and ``<<=``. Python
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classes can override the augmented assignment operators by defining methods
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named :meth:`!__iadd__`, :meth:`!__isub__`, etc. For example, the following
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:class:`!Number` class stores a number and supports using += to create a new
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instance with an incremented value.
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.. The empty groups below prevent conversion to guillemets.
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::
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class Number:
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def __init__(self, value):
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self.value = value
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def __iadd__(self, increment):
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return Number( self.value + increment)
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n = Number(5)
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n += 3
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print n.value
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The :meth:`!__iadd__` special method is called with the value of the increment,
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and should return a new instance with an appropriately modified value; this
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return value is bound as the new value of the variable on the left-hand side.
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Augmented assignment operators were first introduced in the C programming
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language, and most C-derived languages, such as :program:`awk`, C++, Java, Perl,
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and PHP also support them. The augmented assignment patch was implemented by
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Thomas Wouters.
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.. ======================================================================
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String Methods
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==============
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Until now string-manipulation functionality was in the :mod:`string` module,
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which was usually a front-end for the :mod:`!strop` module written in C. The
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addition of Unicode posed a difficulty for the :mod:`!strop` module, because the
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functions would all need to be rewritten in order to accept either 8-bit or
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Unicode strings. For functions such as :func:`!string.replace`, which takes 3
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string arguments, that means eight possible permutations, and correspondingly
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complicated code.
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Instead, Python 2.0 pushes the problem onto the string type, making string
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manipulation functionality available through methods on both 8-bit strings and
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Unicode strings. ::
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>>> 'andrew'.capitalize()
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'Andrew'
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>>> 'hostname'.replace('os', 'linux')
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'hlinuxtname'
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>>> 'moshe'.find('sh')
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2
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One thing that hasn't changed, a noteworthy April Fools' joke notwithstanding,
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is that Python strings are immutable. Thus, the string methods return new
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strings, and do not modify the string on which they operate.
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The old :mod:`string` module is still around for backwards compatibility, but it
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mostly acts as a front-end to the new string methods.
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Two methods which have no parallel in pre-2.0 versions, although they did exist
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in JPython for quite some time, are :meth:`!startswith` and :meth:`!endswith`.
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``s.startswith(t)`` is equivalent to ``s[:len(t)] == t``, while
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``s.endswith(t)`` is equivalent to ``s[-len(t):] == t``.
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One other method which deserves special mention is :meth:`!join`. The
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:meth:`!join` method of a string receives one parameter, a sequence of strings,
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and is equivalent to the :func:`!string.join` function from the old :mod:`string`
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module, with the arguments reversed. In other words, ``s.join(seq)`` is
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equivalent to the old ``string.join(seq, s)``.
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.. ======================================================================
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Garbage Collection of Cycles
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============================
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The C implementation of Python uses reference counting to implement garbage
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collection. Every Python object maintains a count of the number of references
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pointing to itself, and adjusts the count as references are created or
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destroyed. Once the reference count reaches zero, the object is no longer
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accessible, since you need to have a reference to an object to access it, and if
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the count is zero, no references exist any longer.
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Reference counting has some pleasant properties: it's easy to understand and
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implement, and the resulting implementation is portable, fairly fast, and reacts
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well with other libraries that implement their own memory handling schemes. The
|
|
major problem with reference counting is that it sometimes doesn't realise that
|
|
objects are no longer accessible, resulting in a memory leak. This happens when
|
|
there are cycles of references.
|
|
|
|
Consider the simplest possible cycle, a class instance which has a reference to
|
|
itself::
|
|
|
|
instance = SomeClass()
|
|
instance.myself = instance
|
|
|
|
After the above two lines of code have been executed, the reference count of
|
|
``instance`` is 2; one reference is from the variable named ``'instance'``, and
|
|
the other is from the ``myself`` attribute of the instance.
|
|
|
|
If the next line of code is ``del instance``, what happens? The reference count
|
|
of ``instance`` is decreased by 1, so it has a reference count of 1; the
|
|
reference in the ``myself`` attribute still exists. Yet the instance is no
|
|
longer accessible through Python code, and it could be deleted. Several objects
|
|
can participate in a cycle if they have references to each other, causing all of
|
|
the objects to be leaked.
|
|
|
|
Python 2.0 fixes this problem by periodically executing a cycle detection
|
|
algorithm which looks for inaccessible cycles and deletes the objects involved.
|
|
A new :mod:`gc` module provides functions to perform a garbage collection,
|
|
obtain debugging statistics, and tuning the collector's parameters.
|
|
|
|
Running the cycle detection algorithm takes some time, and therefore will result
|
|
in some additional overhead. It is hoped that after we've gotten experience
|
|
with the cycle collection from using 2.0, Python 2.1 will be able to minimize
|
|
the overhead with careful tuning. It's not yet obvious how much performance is
|
|
lost, because benchmarking this is tricky and depends crucially on how often the
|
|
program creates and destroys objects. The detection of cycles can be disabled
|
|
when Python is compiled, if you can't afford even a tiny speed penalty or
|
|
suspect that the cycle collection is buggy, by specifying the
|
|
:option:`!--without-cycle-gc` switch when running the :program:`configure`
|
|
script.
|
|
|
|
Several people tackled this problem and contributed to a solution. An early
|
|
implementation of the cycle detection approach was written by Toby Kelsey. The
|
|
current algorithm was suggested by Eric Tiedemann during a visit to CNRI, and
|
|
Guido van Rossum and Neil Schemenauer wrote two different implementations, which
|
|
were later integrated by Neil. Lots of other people offered suggestions along
|
|
the way; the March 2000 archives of the python-dev mailing list contain most of
|
|
the relevant discussion, especially in the threads titled "Reference cycle
|
|
collection for Python" and "Finalization again".
|
|
|
|
.. ======================================================================
|
|
|
|
|
|
Other Core Changes
|
|
==================
|
|
|
|
Various minor changes have been made to Python's syntax and built-in functions.
|
|
None of the changes are very far-reaching, but they're handy conveniences.
|
|
|
|
|
|
Minor Language Changes
|
|
----------------------
|
|
|
|
A new syntax makes it more convenient to call a given function with a tuple of
|
|
arguments and/or a dictionary of keyword arguments. In Python 1.5 and earlier,
|
|
you'd use the :func:`!apply` built-in function: ``apply(f, args, kw)`` calls the
|
|
function :func:`!f` with the argument tuple *args* and the keyword arguments in
|
|
the dictionary *kw*. :func:`!apply` is the same in 2.0, but thanks to a patch
|
|
from Greg Ewing, ``f(*args, **kw)`` is a shorter and clearer way to achieve the
|
|
same effect. This syntax is symmetrical with the syntax for defining
|
|
functions::
|
|
|
|
def f(*args, **kw):
|
|
# args is a tuple of positional args,
|
|
# kw is a dictionary of keyword args
|
|
...
|
|
|
|
The ``print`` statement can now have its output directed to a file-like
|
|
object by following the ``print`` with ``>> file``, similar to the
|
|
redirection operator in Unix shells. Previously you'd either have to use the
|
|
:meth:`!write` method of the file-like object, which lacks the convenience and
|
|
simplicity of ``print``, or you could assign a new value to
|
|
``sys.stdout`` and then restore the old value. For sending output to standard
|
|
error, it's much easier to write this::
|
|
|
|
print >> sys.stderr, "Warning: action field not supplied"
|
|
|
|
Modules can now be renamed on importing them, using the syntax ``import module
|
|
as name`` or ``from module import name as othername``. The patch was submitted
|
|
by Thomas Wouters.
|
|
|
|
A new format style is available when using the ``%`` operator; '%r' will insert
|
|
the :func:`repr` of its argument. This was also added from symmetry
|
|
considerations, this time for symmetry with the existing '%s' format style,
|
|
which inserts the :func:`str` of its argument. For example, ``'%r %s' % ('abc',
|
|
'abc')`` returns a string containing ``'abc' abc``.
|
|
|
|
Previously there was no way to implement a class that overrode Python's built-in
|
|
:keyword:`in` operator and implemented a custom version. ``obj in seq`` returns
|
|
true if *obj* is present in the sequence *seq*; Python computes this by simply
|
|
trying every index of the sequence until either *obj* is found or an
|
|
:exc:`IndexError` is encountered. Moshe Zadka contributed a patch which adds a
|
|
:meth:`!__contains__` magic method for providing a custom implementation for
|
|
:keyword:`!in`. Additionally, new built-in objects written in C can define what
|
|
:keyword:`!in` means for them via a new slot in the sequence protocol.
|
|
|
|
Earlier versions of Python used a recursive algorithm for deleting objects.
|
|
Deeply nested data structures could cause the interpreter to fill up the C stack
|
|
and crash; Christian Tismer rewrote the deletion logic to fix this problem. On
|
|
a related note, comparing recursive objects recursed infinitely and crashed;
|
|
Jeremy Hylton rewrote the code to no longer crash, producing a useful result
|
|
instead. For example, after this code::
|
|
|
|
a = []
|
|
b = []
|
|
a.append(a)
|
|
b.append(b)
|
|
|
|
The comparison ``a==b`` returns true, because the two recursive data structures
|
|
are isomorphic. See the thread "trashcan and PR#7" in the April 2000 archives of
|
|
the python-dev mailing list for the discussion leading up to this
|
|
implementation, and some useful relevant links. Note that comparisons can now
|
|
also raise exceptions. In earlier versions of Python, a comparison operation
|
|
such as ``cmp(a,b)`` would always produce an answer, even if a user-defined
|
|
:meth:`!__cmp__` method encountered an error, since the resulting exception would
|
|
simply be silently swallowed.
|
|
|
|
.. Starting URL:
|
|
.. https://www.python.org/pipermail/python-dev/2000-April/004834.html
|
|
|
|
Work has been done on porting Python to 64-bit Windows on the Itanium processor,
|
|
mostly by Trent Mick of ActiveState. (Confusingly, ``sys.platform`` is still
|
|
``'win32'`` on Win64 because it seems that for ease of porting, MS Visual C++
|
|
treats code as 32 bit on Itanium.) PythonWin also supports Windows CE; see the
|
|
Python CE page at https://pythonce.sourceforge.net/ for more information.
|
|
|
|
Another new platform is Darwin/MacOS X; initial support for it is in Python 2.0.
|
|
Dynamic loading works, if you specify "configure --with-dyld --with-suffix=.x".
|
|
Consult the README in the Python source distribution for more instructions.
|
|
|
|
An attempt has been made to alleviate one of Python's warts, the often-confusing
|
|
:exc:`NameError` exception when code refers to a local variable before the
|
|
variable has been assigned a value. For example, the following code raises an
|
|
exception on the ``print`` statement in both 1.5.2 and 2.0; in 1.5.2 a
|
|
:exc:`NameError` exception is raised, while 2.0 raises a new
|
|
:exc:`UnboundLocalError` exception. :exc:`UnboundLocalError` is a subclass of
|
|
:exc:`NameError`, so any existing code that expects :exc:`NameError` to be
|
|
raised should still work. ::
|
|
|
|
def f():
|
|
print "i=",i
|
|
i = i + 1
|
|
f()
|
|
|
|
Two new exceptions, :exc:`TabError` and :exc:`IndentationError`, have been
|
|
introduced. They're both subclasses of :exc:`SyntaxError`, and are raised when
|
|
Python code is found to be improperly indented.
|
|
|
|
|
|
Changes to Built-in Functions
|
|
-----------------------------
|
|
|
|
A new built-in, ``zip(seq1, seq2, ...)``, has been added. :func:`zip`
|
|
returns a list of tuples where each tuple contains the i-th element from each of
|
|
the argument sequences. The difference between :func:`zip` and ``map(None,
|
|
seq1, seq2)`` is that :func:`map` pads the sequences with ``None`` if the
|
|
sequences aren't all of the same length, while :func:`zip` truncates the
|
|
returned list to the length of the shortest argument sequence.
|
|
|
|
The :func:`int` and :func:`!long` functions now accept an optional "base"
|
|
parameter when the first argument is a string. ``int('123', 10)`` returns 123,
|
|
while ``int('123', 16)`` returns 291. ``int(123, 16)`` raises a
|
|
:exc:`TypeError` exception with the message "can't convert non-string with
|
|
explicit base".
|
|
|
|
A new variable holding more detailed version information has been added to the
|
|
:mod:`sys` module. ``sys.version_info`` is a tuple ``(major, minor, micro,
|
|
level, serial)`` For example, in a hypothetical 2.0.1beta1, ``sys.version_info``
|
|
would be ``(2, 0, 1, 'beta', 1)``. *level* is a string such as ``"alpha"``,
|
|
``"beta"``, or ``"final"`` for a final release.
|
|
|
|
Dictionaries have an odd new method, ``setdefault(key, default)``, which
|
|
behaves similarly to the existing :meth:`!get` method. However, if the key is
|
|
missing, :meth:`!setdefault` both returns the value of *default* as :meth:`!get`
|
|
would do, and also inserts it into the dictionary as the value for *key*. Thus,
|
|
the following lines of code::
|
|
|
|
if dict.has_key( key ): return dict[key]
|
|
else:
|
|
dict[key] = []
|
|
return dict[key]
|
|
|
|
can be reduced to a single ``return dict.setdefault(key, [])`` statement.
|
|
|
|
The interpreter sets a maximum recursion depth in order to catch runaway
|
|
recursion before filling the C stack and causing a core dump or GPF..
|
|
Previously this limit was fixed when you compiled Python, but in 2.0 the maximum
|
|
recursion depth can be read and modified using :func:`sys.getrecursionlimit` and
|
|
:func:`sys.setrecursionlimit`. The default value is 1000, and a rough maximum
|
|
value for a given platform can be found by running a new script,
|
|
:file:`Misc/find_recursionlimit.py`.
|
|
|
|
.. ======================================================================
|
|
|
|
|
|
Porting to 2.0
|
|
==============
|
|
|
|
New Python releases try hard to be compatible with previous releases, and the
|
|
record has been pretty good. However, some changes are considered useful
|
|
enough, usually because they fix initial design decisions that turned out to be
|
|
actively mistaken, that breaking backward compatibility can't always be avoided.
|
|
This section lists the changes in Python 2.0 that may cause old Python code to
|
|
break.
|
|
|
|
The change which will probably break the most code is tightening up the
|
|
arguments accepted by some methods. Some methods would take multiple arguments
|
|
and treat them as a tuple, particularly various list methods such as
|
|
:meth:`!append` and :meth:`!insert`. In earlier versions of Python, if ``L`` is
|
|
a list, ``L.append( 1,2 )`` appends the tuple ``(1,2)`` to the list. In Python
|
|
2.0 this causes a :exc:`TypeError` exception to be raised, with the message:
|
|
'append requires exactly 1 argument; 2 given'. The fix is to simply add an
|
|
extra set of parentheses to pass both values as a tuple: ``L.append( (1,2) )``.
|
|
|
|
The earlier versions of these methods were more forgiving because they used an
|
|
old function in Python's C interface to parse their arguments; 2.0 modernizes
|
|
them to use :c:func:`PyArg_ParseTuple`, the current argument parsing function,
|
|
which provides more helpful error messages and treats multi-argument calls as
|
|
errors. If you absolutely must use 2.0 but can't fix your code, you can edit
|
|
:file:`Objects/listobject.c` and define the preprocessor symbol
|
|
``NO_STRICT_LIST_APPEND`` to preserve the old behaviour; this isn't recommended.
|
|
|
|
Some of the functions in the :mod:`socket` module are still forgiving in this
|
|
way. For example, ``socket.connect( ('hostname', 25) )`` is the correct
|
|
form, passing a tuple representing an IP address, but ``socket.connect('hostname', 25)``
|
|
also works. :meth:`socket.connect_ex <socket.socket.connect_ex>` and :meth:`socket.bind <socket.socket.bind>`
|
|
are similarly easy-going. 2.0alpha1 tightened these functions up, but because
|
|
the documentation actually used the erroneous multiple argument form, many
|
|
people wrote code which would break with the stricter checking. GvR backed out
|
|
the changes in the face of public reaction, so for the :mod:`socket` module, the
|
|
documentation was fixed and the multiple argument form is simply marked as
|
|
deprecated; it *will* be tightened up again in a future Python version.
|
|
|
|
The ``\x`` escape in string literals now takes exactly 2 hex digits. Previously
|
|
it would consume all the hex digits following the 'x' and take the lowest 8 bits
|
|
of the result, so ``\x123456`` was equivalent to ``\x56``.
|
|
|
|
The :exc:`AttributeError` and :exc:`NameError` exceptions have a more friendly
|
|
error message, whose text will be something like ``'Spam' instance has no
|
|
attribute 'eggs'`` or ``name 'eggs' is not defined``. Previously the error
|
|
message was just the missing attribute name ``eggs``, and code written to take
|
|
advantage of this fact will break in 2.0.
|
|
|
|
Some work has been done to make integers and long integers a bit more
|
|
interchangeable. In 1.5.2, large-file support was added for Solaris, to allow
|
|
reading files larger than 2 GiB; this made the :meth:`!tell` method of file
|
|
objects return a long integer instead of a regular integer. Some code would
|
|
subtract two file offsets and attempt to use the result to multiply a sequence
|
|
or slice a string, but this raised a :exc:`TypeError`. In 2.0, long integers
|
|
can be used to multiply or slice a sequence, and it'll behave as you'd
|
|
intuitively expect it to; ``3L * 'abc'`` produces 'abcabcabc', and
|
|
``(0,1,2,3)[2L:4L]`` produces (2,3). Long integers can also be used in various
|
|
contexts where previously only integers were accepted, such as in the
|
|
:meth:`!seek` method of file objects, and in the formats supported by the ``%``
|
|
operator (``%d``, ``%i``, ``%x``, etc.). For example, ``"%d" % 2L**64`` will
|
|
produce the string ``18446744073709551616``.
|
|
|
|
The subtlest long integer change of all is that the :func:`str` of a long
|
|
integer no longer has a trailing 'L' character, though :func:`repr` still
|
|
includes it. The 'L' annoyed many people who wanted to print long integers that
|
|
looked just like regular integers, since they had to go out of their way to chop
|
|
off the character. This is no longer a problem in 2.0, but code which does
|
|
``str(longval)[:-1]`` and assumes the 'L' is there, will now lose the final
|
|
digit.
|
|
|
|
Taking the :func:`repr` of a float now uses a different formatting precision
|
|
than :func:`str`. :func:`repr` uses ``%.17g`` format string for C's
|
|
:func:`!sprintf`, while :func:`str` uses ``%.12g`` as before. The effect is that
|
|
:func:`repr` may occasionally show more decimal places than :func:`str`, for
|
|
certain numbers. For example, the number 8.1 can't be represented exactly in
|
|
binary, so ``repr(8.1)`` is ``'8.0999999999999996'``, while str(8.1) is
|
|
``'8.1'``.
|
|
|
|
The ``-X`` command-line option, which turned all standard exceptions into
|
|
strings instead of classes, has been removed; the standard exceptions will now
|
|
always be classes. The :mod:`!exceptions` module containing the standard
|
|
exceptions was translated from Python to a built-in C module, written by Barry
|
|
Warsaw and Fredrik Lundh.
|
|
|
|
.. Commented out for now -- I don't think anyone will care.
|
|
The pattern and match objects provided by SRE are C types, not Python
|
|
class instances as in 1.5. This means you can no longer inherit from
|
|
\class{RegexObject} or \class{MatchObject}, but that shouldn't be much
|
|
of a problem since no one should have been doing that in the first
|
|
place.
|
|
.. ======================================================================
|
|
|
|
|
|
Extending/Embedding Changes
|
|
===========================
|
|
|
|
Some of the changes are under the covers, and will only be apparent to people
|
|
writing C extension modules or embedding a Python interpreter in a larger
|
|
application. If you aren't dealing with Python's C API, you can safely skip
|
|
this section.
|
|
|
|
The version number of the Python C API was incremented, so C extensions compiled
|
|
for 1.5.2 must be recompiled in order to work with 2.0. On Windows, it's not
|
|
possible for Python 2.0 to import a third party extension built for Python 1.5.x
|
|
due to how Windows DLLs work, so Python will raise an exception and the import
|
|
will fail.
|
|
|
|
Users of Jim Fulton's ExtensionClass module will be pleased to find out that
|
|
hooks have been added so that ExtensionClasses are now supported by
|
|
:func:`isinstance` and :func:`issubclass`. This means you no longer have to
|
|
remember to write code such as ``if type(obj) == myExtensionClass``, but can use
|
|
the more natural ``if isinstance(obj, myExtensionClass)``.
|
|
|
|
The :file:`Python/importdl.c` file, which was a mass of #ifdefs to support
|
|
dynamic loading on many different platforms, was cleaned up and reorganised by
|
|
Greg Stein. :file:`importdl.c` is now quite small, and platform-specific code
|
|
has been moved into a bunch of :file:`Python/dynload_\*.c` files. Another
|
|
cleanup: there were also a number of :file:`my\*.h` files in the Include/
|
|
directory that held various portability hacks; they've been merged into a single
|
|
file, :file:`Include/pyport.h`.
|
|
|
|
Vladimir Marangozov's long-awaited malloc restructuring was completed, to make
|
|
it easy to have the Python interpreter use a custom allocator instead of C's
|
|
standard :c:func:`malloc`. For documentation, read the comments in
|
|
:file:`Include/pymem.h` and :file:`Include/objimpl.h`. For the lengthy
|
|
discussions during which the interface was hammered out, see the web archives of
|
|
the 'patches' and 'python-dev' lists at python.org.
|
|
|
|
Recent versions of the GUSI development environment for MacOS support POSIX
|
|
threads. Therefore, Python's POSIX threading support now works on the
|
|
Macintosh. Threading support using the user-space GNU ``pth`` library was also
|
|
contributed.
|
|
|
|
Threading support on Windows was enhanced, too. Windows supports thread locks
|
|
that use kernel objects only in case of contention; in the common case when
|
|
there's no contention, they use simpler functions which are an order of
|
|
magnitude faster. A threaded version of Python 1.5.2 on NT is twice as slow as
|
|
an unthreaded version; with the 2.0 changes, the difference is only 10%. These
|
|
improvements were contributed by Yakov Markovitch.
|
|
|
|
Python 2.0's source now uses only ANSI C prototypes, so compiling Python now
|
|
requires an ANSI C compiler, and can no longer be done using a compiler that
|
|
only supports K&R C.
|
|
|
|
Previously the Python virtual machine used 16-bit numbers in its bytecode,
|
|
limiting the size of source files. In particular, this affected the maximum
|
|
size of literal lists and dictionaries in Python source; occasionally people who
|
|
are generating Python code would run into this limit. A patch by Charles G.
|
|
Waldman raises the limit from ``2**16`` to ``2**32``.
|
|
|
|
Three new convenience functions intended for adding constants to a module's
|
|
dictionary at module initialization time were added: :c:func:`PyModule_AddObject`,
|
|
:c:func:`PyModule_AddIntConstant`, and :c:func:`PyModule_AddStringConstant`. Each
|
|
of these functions takes a module object, a null-terminated C string containing
|
|
the name to be added, and a third argument for the value to be assigned to the
|
|
name. This third argument is, respectively, a Python object, a C long, or a C
|
|
string.
|
|
|
|
A wrapper API was added for Unix-style signal handlers. :c:func:`PyOS_getsig` gets
|
|
a signal handler and :c:func:`PyOS_setsig` will set a new handler.
|
|
|
|
.. ======================================================================
|
|
|
|
|
|
Distutils: Making Modules Easy to Install
|
|
=========================================
|
|
|
|
Before Python 2.0, installing modules was a tedious affair -- there was no way
|
|
to figure out automatically where Python is installed, or what compiler options
|
|
to use for extension modules. Software authors had to go through an arduous
|
|
ritual of editing Makefiles and configuration files, which only really work on
|
|
Unix and leave Windows and MacOS unsupported. Python users faced wildly
|
|
differing installation instructions which varied between different extension
|
|
packages, which made administering a Python installation something of a chore.
|
|
|
|
The SIG for distribution utilities, shepherded by Greg Ward, has created the
|
|
Distutils, a system to make package installation much easier. They form the
|
|
``distutils`` package, a new part of Python's standard library. In the best
|
|
case, installing a Python module from source will require the same steps: first
|
|
you simply mean unpack the tarball or zip archive, and the run "``python
|
|
setup.py install``". The platform will be automatically detected, the compiler
|
|
will be recognized, C extension modules will be compiled, and the distribution
|
|
installed into the proper directory. Optional command-line arguments provide
|
|
more control over the installation process, the distutils package offers many
|
|
places to override defaults -- separating the build from the install, building
|
|
or installing in non-default directories, and more.
|
|
|
|
In order to use the Distutils, you need to write a :file:`setup.py` script. For
|
|
the simple case, when the software contains only .py files, a minimal
|
|
:file:`setup.py` can be just a few lines long::
|
|
|
|
from distutils.core import setup
|
|
setup (name = "foo", version = "1.0",
|
|
py_modules = ["module1", "module2"])
|
|
|
|
The :file:`setup.py` file isn't much more complicated if the software consists
|
|
of a few packages::
|
|
|
|
from distutils.core import setup
|
|
setup (name = "foo", version = "1.0",
|
|
packages = ["package", "package.subpackage"])
|
|
|
|
A C extension can be the most complicated case; here's an example taken from
|
|
the PyXML package::
|
|
|
|
from distutils.core import setup, Extension
|
|
|
|
expat_extension = Extension('xml.parsers.pyexpat',
|
|
define_macros = [('XML_NS', None)],
|
|
include_dirs = [ 'extensions/expat/xmltok',
|
|
'extensions/expat/xmlparse' ],
|
|
sources = [ 'extensions/pyexpat.c',
|
|
'extensions/expat/xmltok/xmltok.c',
|
|
'extensions/expat/xmltok/xmlrole.c', ]
|
|
)
|
|
setup (name = "PyXML", version = "0.5.4",
|
|
ext_modules =[ expat_extension ] )
|
|
|
|
The Distutils can also take care of creating source and binary distributions.
|
|
The "sdist" command, run by "``python setup.py sdist``', builds a source
|
|
distribution such as :file:`foo-1.0.tar.gz`. Adding new commands isn't
|
|
difficult, "bdist_rpm" and "bdist_wininst" commands have already been
|
|
contributed to create an RPM distribution and a Windows installer for the
|
|
software, respectively. Commands to create other distribution formats such as
|
|
Debian packages and Solaris :file:`.pkg` files are in various stages of
|
|
development.
|
|
|
|
All this is documented in a new manual, *Distributing Python Modules*, that
|
|
joins the basic set of Python documentation.
|
|
|
|
.. ======================================================================
|
|
|
|
|
|
XML Modules
|
|
===========
|
|
|
|
Python 1.5.2 included a simple XML parser in the form of the :mod:`!xmllib`
|
|
module, contributed by Sjoerd Mullender. Since 1.5.2's release, two different
|
|
interfaces for processing XML have become common: SAX2 (version 2 of the Simple
|
|
API for XML) provides an event-driven interface with some similarities to
|
|
:mod:`!xmllib`, and the DOM (Document Object Model) provides a tree-based
|
|
interface, transforming an XML document into a tree of nodes that can be
|
|
traversed and modified. Python 2.0 includes a SAX2 interface and a stripped-down
|
|
DOM interface as part of the :mod:`xml` package. Here we will give a brief
|
|
overview of these new interfaces; consult the Python documentation or the source
|
|
code for complete details. The Python XML SIG is also working on improved
|
|
documentation.
|
|
|
|
|
|
SAX2 Support
|
|
------------
|
|
|
|
SAX defines an event-driven interface for parsing XML. To use SAX, you must
|
|
write a SAX handler class. Handler classes inherit from various classes
|
|
provided by SAX, and override various methods that will then be called by the
|
|
XML parser. For example, the :meth:`~xml.sax.handler.ContentHandler.startElement` and :meth:`~xml.sax.handler.ContentHandler.endElement`
|
|
methods are called for every starting and end tag encountered by the parser, the
|
|
:meth:`~xml.sax.handler.ContentHandler.characters` method is called for every chunk of character data, and so
|
|
forth.
|
|
|
|
The advantage of the event-driven approach is that the whole document doesn't
|
|
have to be resident in memory at any one time, which matters if you are
|
|
processing really huge documents. However, writing the SAX handler class can
|
|
get very complicated if you're trying to modify the document structure in some
|
|
elaborate way.
|
|
|
|
For example, this little example program defines a handler that prints a message
|
|
for every starting and ending tag, and then parses the file :file:`hamlet.xml`
|
|
using it::
|
|
|
|
from xml import sax
|
|
|
|
class SimpleHandler(sax.ContentHandler):
|
|
def startElement(self, name, attrs):
|
|
print 'Start of element:', name, attrs.keys()
|
|
|
|
def endElement(self, name):
|
|
print 'End of element:', name
|
|
|
|
# Create a parser object
|
|
parser = sax.make_parser()
|
|
|
|
# Tell it what handler to use
|
|
handler = SimpleHandler()
|
|
parser.setContentHandler( handler )
|
|
|
|
# Parse a file!
|
|
parser.parse( 'hamlet.xml' )
|
|
|
|
For more information, consult the Python documentation, or the XML HOWTO at
|
|
https://pyxml.sourceforge.net/topics/howto/xml-howto.html.
|
|
|
|
|
|
DOM Support
|
|
-----------
|
|
|
|
The Document Object Model is a tree-based representation for an XML document. A
|
|
top-level :class:`!Document` instance is the root of the tree, and has a single
|
|
child which is the top-level :class:`!Element` instance. This :class:`!Element`
|
|
has children nodes representing character data and any sub-elements, which may
|
|
have further children of their own, and so forth. Using the DOM you can
|
|
traverse the resulting tree any way you like, access element and attribute
|
|
values, insert and delete nodes, and convert the tree back into XML.
|
|
|
|
The DOM is useful for modifying XML documents, because you can create a DOM
|
|
tree, modify it by adding new nodes or rearranging subtrees, and then produce a
|
|
new XML document as output. You can also construct a DOM tree manually and
|
|
convert it to XML, which can be a more flexible way of producing XML output than
|
|
simply writing ``<tag1>``...\ ``</tag1>`` to a file.
|
|
|
|
The DOM implementation included with Python lives in the :mod:`xml.dom.minidom`
|
|
module. It's a lightweight implementation of the Level 1 DOM with support for
|
|
XML namespaces. The :func:`!parse` and :func:`!parseString` convenience
|
|
functions are provided for generating a DOM tree::
|
|
|
|
from xml.dom import minidom
|
|
doc = minidom.parse('hamlet.xml')
|
|
|
|
``doc`` is a :class:`!Document` instance. :class:`!Document`, like all the other
|
|
DOM classes such as :class:`!Element` and :class:`Text`, is a subclass of the
|
|
:class:`!Node` base class. All the nodes in a DOM tree therefore support certain
|
|
common methods, such as :meth:`!toxml` which returns a string containing the XML
|
|
representation of the node and its children. Each class also has special
|
|
methods of its own; for example, :class:`!Element` and :class:`!Document`
|
|
instances have a method to find all child elements with a given tag name.
|
|
Continuing from the previous 2-line example::
|
|
|
|
perslist = doc.getElementsByTagName( 'PERSONA' )
|
|
print perslist[0].toxml()
|
|
print perslist[1].toxml()
|
|
|
|
For the *Hamlet* XML file, the above few lines output::
|
|
|
|
<PERSONA>CLAUDIUS, king of Denmark. </PERSONA>
|
|
<PERSONA>HAMLET, son to the late, and nephew to the present king.</PERSONA>
|
|
|
|
The root element of the document is available as ``doc.documentElement``, and
|
|
its children can be easily modified by deleting, adding, or removing nodes::
|
|
|
|
root = doc.documentElement
|
|
|
|
# Remove the first child
|
|
root.removeChild( root.childNodes[0] )
|
|
|
|
# Move the new first child to the end
|
|
root.appendChild( root.childNodes[0] )
|
|
|
|
# Insert the new first child (originally,
|
|
# the third child) before the 20th child.
|
|
root.insertBefore( root.childNodes[0], root.childNodes[20] )
|
|
|
|
Again, I will refer you to the Python documentation for a complete listing of
|
|
the different :class:`!Node` classes and their various methods.
|
|
|
|
|
|
Relationship to PyXML
|
|
---------------------
|
|
|
|
The XML Special Interest Group has been working on XML-related Python code for a
|
|
while. Its code distribution, called PyXML, is available from the SIG's web
|
|
pages at https://www.python.org/community/sigs/current/xml-sig. The PyXML distribution also used
|
|
the package name ``xml``. If you've written programs that used PyXML, you're
|
|
probably wondering about its compatibility with the 2.0 :mod:`xml` package.
|
|
|
|
The answer is that Python 2.0's :mod:`xml` package isn't compatible with PyXML,
|
|
but can be made compatible by installing a recent version PyXML. Many
|
|
applications can get by with the XML support that is included with Python 2.0,
|
|
but more complicated applications will require that the full PyXML package will
|
|
be installed. When installed, PyXML versions 0.6.0 or greater will replace the
|
|
:mod:`xml` package shipped with Python, and will be a strict superset of the
|
|
standard package, adding a bunch of additional features. Some of the additional
|
|
features in PyXML include:
|
|
|
|
* 4DOM, a full DOM implementation from FourThought, Inc.
|
|
|
|
* The xmlproc validating parser, written by Lars Marius Garshol.
|
|
|
|
* The :mod:`!sgmlop` parser accelerator module, written by Fredrik Lundh.
|
|
|
|
.. ======================================================================
|
|
|
|
|
|
Module changes
|
|
==============
|
|
|
|
Lots of improvements and bugfixes were made to Python's extensive standard
|
|
library; some of the affected modules include :mod:`readline`,
|
|
:mod:`ConfigParser <configparser>`, :mod:`!cgi`, :mod:`calendar`, :mod:`posix`, :mod:`readline`,
|
|
:mod:`!xmllib`, :mod:`!aifc`, :mod:`!chunk`, :mod:`wave`, :mod:`random`, :mod:`shelve`,
|
|
and :mod:`!nntplib`. Consult the CVS logs for the exact patch-by-patch details.
|
|
|
|
Brian Gallew contributed OpenSSL support for the :mod:`socket` module. OpenSSL
|
|
is an implementation of the Secure Socket Layer, which encrypts the data being
|
|
sent over a socket. When compiling Python, you can edit :file:`Modules/Setup`
|
|
to include SSL support, which adds an additional function to the :mod:`socket`
|
|
module: ``socket.ssl(socket, keyfile, certfile)``, which takes a socket
|
|
object and returns an SSL socket. The :mod:`httplib <http>` and :mod:`urllib` modules
|
|
were also changed to support ``https://`` URLs, though no one has implemented
|
|
FTP or SMTP over SSL.
|
|
|
|
The :mod:`httplib <http>` module has been rewritten by Greg Stein to support HTTP/1.1.
|
|
|
|
Backward compatibility with the 1.5 version of :mod:`!httplib` is provided,
|
|
though using HTTP/1.1 features such as pipelining will require rewriting code to
|
|
use a different set of interfaces.
|
|
|
|
The :mod:`!Tkinter` module now supports Tcl/Tk version 8.1, 8.2, or 8.3, and
|
|
support for the older 7.x versions has been dropped. The Tkinter module now
|
|
supports displaying Unicode strings in Tk widgets. Also, Fredrik Lundh
|
|
contributed an optimization which makes operations like ``create_line`` and
|
|
``create_polygon`` much faster, especially when using lots of coordinates.
|
|
|
|
The :mod:`curses` module has been greatly extended, starting from Oliver
|
|
Andrich's enhanced version, to provide many additional functions from ncurses
|
|
and SYSV curses, such as colour, alternative character set support, pads, and
|
|
mouse support. This means the module is no longer compatible with operating
|
|
systems that only have BSD curses, but there don't seem to be any currently
|
|
maintained OSes that fall into this category.
|
|
|
|
As mentioned in the earlier discussion of 2.0's Unicode support, the underlying
|
|
implementation of the regular expressions provided by the :mod:`re` module has
|
|
been changed. SRE, a new regular expression engine written by Fredrik Lundh and
|
|
partially funded by Hewlett Packard, supports matching against both 8-bit
|
|
strings and Unicode strings.
|
|
|
|
.. ======================================================================
|
|
|
|
|
|
New modules
|
|
===========
|
|
|
|
A number of new modules were added. We'll simply list them with brief
|
|
descriptions; consult the 2.0 documentation for the details of a particular
|
|
module.
|
|
|
|
* :mod:`atexit`: For registering functions to be called before the Python
|
|
interpreter exits. Code that currently sets ``sys.exitfunc`` directly should be
|
|
changed to use the :mod:`atexit` module instead, importing :mod:`atexit` and
|
|
calling :func:`atexit.register` with the function to be called on exit.
|
|
(Contributed by Skip Montanaro.)
|
|
|
|
* :mod:`codecs`, :mod:`!encodings`, :mod:`unicodedata`: Added as part of the new
|
|
Unicode support.
|
|
|
|
* :mod:`filecmp`: Supersedes the old :mod:`!cmp`, :mod:`!cmpcache` and
|
|
:mod:`!dircmp` modules, which have now become deprecated. (Contributed by Gordon
|
|
MacMillan and Moshe Zadka.)
|
|
|
|
* :mod:`gettext`: This module provides internationalization (I18N) and
|
|
localization (L10N) support for Python programs by providing an interface to the
|
|
GNU gettext message catalog library. (Integrated by Barry Warsaw, from separate
|
|
contributions by Martin von Löwis, Peter Funk, and James Henstridge.)
|
|
|
|
* :mod:`!linuxaudiodev`: Support for the :file:`/dev/audio` device on Linux, a
|
|
twin to the existing :mod:`!sunaudiodev` module. (Contributed by Peter Bosch,
|
|
with fixes by Jeremy Hylton.)
|
|
|
|
* :mod:`mmap`: An interface to memory-mapped files on both Windows and Unix. A
|
|
file's contents can be mapped directly into memory, at which point it behaves
|
|
like a mutable string, so its contents can be read and modified. They can even
|
|
be passed to functions that expect ordinary strings, such as the :mod:`re`
|
|
module. (Contributed by Sam Rushing, with some extensions by A.M. Kuchling.)
|
|
|
|
* :mod:`!pyexpat`: An interface to the Expat XML parser. (Contributed by Paul
|
|
Prescod.)
|
|
|
|
* :mod:`robotparser <urllib.robotparser>`: Parse a :file:`robots.txt` file, which is used for writing
|
|
web spiders that politely avoid certain areas of a web site. The parser accepts
|
|
the contents of a :file:`robots.txt` file, builds a set of rules from it, and
|
|
can then answer questions about the fetchability of a given URL. (Contributed
|
|
by Skip Montanaro.)
|
|
|
|
* :mod:`tabnanny`: A module/script to check Python source code for ambiguous
|
|
indentation. (Contributed by Tim Peters.)
|
|
|
|
* :mod:`!UserString`: A base class useful for deriving objects that behave like
|
|
strings.
|
|
|
|
* :mod:`webbrowser`: A module that provides a platform independent way to launch
|
|
a web browser on a specific URL. For each platform, various browsers are tried
|
|
in a specific order. The user can alter which browser is launched by setting the
|
|
*BROWSER* environment variable. (Originally inspired by Eric S. Raymond's patch
|
|
to :mod:`urllib` which added similar functionality, but the final module comes
|
|
from code originally implemented by Fred Drake as
|
|
:file:`Tools/idle/BrowserControl.py`, and adapted for the standard library by
|
|
Fred.)
|
|
|
|
* :mod:`_winreg <winreg>`: An interface to the Windows registry. :mod:`!_winreg` is an
|
|
adaptation of functions that have been part of PythonWin since 1995, but has now
|
|
been added to the core distribution, and enhanced to support Unicode.
|
|
:mod:`!_winreg` was written by Bill Tutt and Mark Hammond.
|
|
|
|
* :mod:`zipfile`: A module for reading and writing ZIP-format archives. These
|
|
are archives produced by :program:`PKZIP` on DOS/Windows or :program:`zip` on
|
|
Unix, not to be confused with :program:`gzip`\ -format files (which are
|
|
supported by the :mod:`gzip` module) (Contributed by James C. Ahlstrom.)
|
|
|
|
* :mod:`!imputil`: A module that provides a simpler way for writing customized
|
|
import hooks, in comparison to the existing :mod:`!ihooks` module. (Implemented
|
|
by Greg Stein, with much discussion on python-dev along the way.)
|
|
|
|
.. ======================================================================
|
|
|
|
|
|
IDLE Improvements
|
|
=================
|
|
|
|
IDLE is the official Python cross-platform IDE, written using Tkinter. Python
|
|
2.0 includes IDLE 0.6, which adds a number of new features and improvements. A
|
|
partial list:
|
|
|
|
* UI improvements and optimizations, especially in the area of syntax
|
|
highlighting and auto-indentation.
|
|
|
|
* The class browser now shows more information, such as the top level functions
|
|
in a module.
|
|
|
|
* Tab width is now a user settable option. When opening an existing Python file,
|
|
IDLE automatically detects the indentation conventions, and adapts.
|
|
|
|
* There is now support for calling browsers on various platforms, used to open
|
|
the Python documentation in a browser.
|
|
|
|
* IDLE now has a command line, which is largely similar to the vanilla Python
|
|
interpreter.
|
|
|
|
* Call tips were added in many places.
|
|
|
|
* IDLE can now be installed as a package.
|
|
|
|
* In the editor window, there is now a line/column bar at the bottom.
|
|
|
|
* Three new keystroke commands: Check module (:kbd:`Alt-F5`), Import module (:kbd:`F5`) and
|
|
Run script (:kbd:`Ctrl-F5`).
|
|
|
|
.. ======================================================================
|
|
|
|
|
|
Deleted and Deprecated Modules
|
|
==============================
|
|
|
|
A few modules have been dropped because they're obsolete, or because there are
|
|
now better ways to do the same thing. The :mod:`!stdwin` module is gone; it was
|
|
for a platform-independent windowing toolkit that's no longer developed.
|
|
|
|
A number of modules have been moved to the :file:`lib-old` subdirectory:
|
|
:mod:`!cmp`, :mod:`!cmpcache`, :mod:`!dircmp`, :mod:`!dump`, :mod:`!find`,
|
|
:mod:`!grep`, :mod:`!packmail`, :mod:`!poly`, :mod:`!util`, :mod:`!whatsound`,
|
|
:mod:`!zmod`. If you have code which relies on a module that's been moved to
|
|
:file:`lib-old`, you can simply add that directory to ``sys.path`` to get them
|
|
back, but you're encouraged to update any code that uses these modules.
|
|
|
|
|
|
Acknowledgements
|
|
================
|
|
|
|
The authors would like to thank the following people for offering suggestions on
|
|
various drafts of this article: David Bolen, Mark Hammond, Gregg Hauser, Jeremy
|
|
Hylton, Fredrik Lundh, Detlef Lannert, Aahz Maruch, Skip Montanaro, Vladimir
|
|
Marangozov, Tobias Polzin, Guido van Rossum, Neil Schemenauer, and Russ Schmidt.
|
|
|