263 lines
9.7 KiB
Plaintext
263 lines
9.7 KiB
Plaintext
PEP: 3000
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Title: Python 3.0 Plans
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Version: $Revision$
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Last-Modified: $Date$
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Author: A.M. Kuchling <amk@amk.ca>,
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Brett Cannon <drifty@alum.berkeley.edu>
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Status: Draft
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Type: Informational
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Content-Type: text/x-rst
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Created: 20-Aug-2004
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Post-History:
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Abstract
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========
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This PEP describes the changes currently envisioned in Python 3.0
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(also called Python 3000), a hypothetical future release of Python that
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can break backwards compatibility with the existing body of Python code.
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The list of features included in this document is subject to change
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and isn't binding on the Python development community; features may be
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added, removed, and modified at any time. The purpose of this list is
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to focus our language development effort on changes that are steps to
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3.0, and to encourage people to invent ways to smooth the transition.
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This document is not a wish-list that anyone can extend. While there
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are two authors of this PEP, we're just supplying the text; the
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decisions for which changes are listed in this document are made by
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Guido van Rossum, who has chosen them as goals for Python 3.0.
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General goals
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=============
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A general goal is to reduce feature duplication by removing old ways
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of doing things. A general principle of the design will be that one
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obvious way of doing something is enough. [1]_
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Core language
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=============
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* Remove distinction between int and long types [1]_
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* True division becomes default behavior [10]_
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* Make all strings be Unicode, and have a separate bytes() type [1]_
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* ``exec`` as a statement is not worth it -- make it a function
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* Add optional declarations for static typing [11]_
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* Support only new-style classes; classic classes will be gone [1]_
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* Return iterators instead of lists where appropriate for atomic type methods
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(e.g. ``dict.keys()``, ``dict.values()``, ``dict.items()``, etc.)
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(Do we keep iter*() methods or remove them? I vote remove. -- nn)
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* Replace ``print`` by a function [16]_
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* Do something so you can catch multiple exceptions using ``except E1,
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E2, E3:``. Maybe use ``except E1, E2, E3 as err:`` if you want the
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error variable? [3]_
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* ``None``, ``True`` and ``False`` become keywords [4]_
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* ``as`` becomes a keyword [5]_
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* Have list comprehensions be syntactic sugar for passing an
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equivalent generator expression to ``list()``; as a consequence the
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loop variable will no longer be exposed [12]_
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* Comparisons other than ``==`` and ``!=`` between disparate types
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will raise an exception unless explicitly supported by the type [6]_
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* Exceptions will grow an attribute to store the traceback [13]_
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* floats will not be acceptable as arguments in place of ints for operations
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where floats are inadvertantly accepted (PyArg_ParseTuple() i & l formats)
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* Imports will be absolute by default.
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Relative imports must be explicitly specified [19]_
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* __init__.py will be optional in sub-packages. __init__.py will still
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be required for top-level packages.
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* Cleanup the Py_InitModule() variants {,3,4} (also import and parser APIs)
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* Cleanup the APIs exported in pythonrun, etc.
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* Fix (or remove) {}.setdefault() [21]_
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* Some expressions will require paretheses that didn't in 2.x:
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- List comprehensions will require parentheses around the iterables.
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This will make list comprehensions more similar to generator comprehensions.
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[x for x in 1, 2] will need to be: [x for x in (1, 2)]
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- Lambdas will have to be parenthesized [23]_
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* Builtin module init function names (PyMODINIT_FUNC) will be prefixed
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with _Py (or Py). Currently they aren't namespace safe since the names
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start with init.
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To be removed:
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* String exceptions: use instances of an Exception class [2]_
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* ``raise Exception, "message"``: use ``raise Exception("message")`` [14]_
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* ```x```: use ``repr(x)`` [2]_
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* The ``<>`` operator: use ``!=`` instead [3]_
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* Unbound methods [7]_
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* METH_OLDARGS
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* __getslice__, __setslice__, __delslice__ [17]_
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* C APIs (see code):
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PyFloat_AsString, PyFloat_AsReprString, PyFloat_AsStringEx,
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PySequence_In, PyEval_EvalFrame, PyEval_CallObject,
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_PyObject_Del, _PyObject_GC_Del, _PyObject_GC_Track, _PyObject_GC_UnTrack
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PyString_AsEncodedString, PyString_AsDecodedString
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typedefs: intargfunc, intintargfunc
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Built-in Namespace
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==================
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* Make built-ins return an iterator where appropriate (e.g. ``range()``,
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``zip()``, etc.)
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* Relevant functions should consume iterators (e.g. ``min()``,
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``max()``)
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* Introduce ``trunc()``, which would call the ``__trunc__()`` method on its
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argument; suggested use is for objects like float where calling ``__int__()``
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has data loss, but an integral representation is still desired [8]_
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* Exception hierarchy changes [20]_
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To be removed:
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* ``apply()``: use ``f(*args, **kw)`` instead [2]_
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* ``buffer()``: must die (use a bytes() type instead) [2]_
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* ``callable()``: just call the object and catch the exception [2]_
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* ``compile()``: put in ``sys`` (or perhaps in a module of its own) [2]_
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* ``coerce()``: no longer needed [2]_
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* ``execfile()``, ``reload()``: use ``exec()`` [2]_
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* ``input()``: use ``eval(sys.stdin.readline())`` [2]_
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* ``intern()``, ``id()``: put in ``sys`` [2]_
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* ``map()``, ``filter()``: use list comprehensions instead [1]_, [9]_
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* ``reduce()``: write a loop instead [2]_, [9]_
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* ``raw_input()``: use ``sys.stdin.readline()`` [2]_
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* ``xrange()``: use ``range()`` instead [1]_
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Atomic Types
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============
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To be removed:
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* ``basestring.find()`` and ``basestring.rfind()``; use ``basestring.index()``
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or ``basestring.rindex()`` in a try/except block [15]_
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* ``file.xreadlines()`` method [17]_
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* ``dict.setdefault()`` [22]_
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Standard library
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================
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* Reorganize the standard library to not be as shallow
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* Move test code to where it belongs, there will be no more test() functions
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in the standard library
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To be removed:
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* Deprecated modules, methods, parameters, attributes, etc. [1]_ [17]_ [18]_
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There may be other modules, the most common are listed below.
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stdlib modules to be removed (see docstrings and comments in the source):
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* ``macfs``, ``new``, ``reconvert``, ``stringold``, ``xmllib``
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* ``pcre``, ``pypcre``, ``strop``
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stdlib modules to be removed (see PEP 4): [18]_
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* ``posixfile``, ``pre``, ``regsub``, ``rfc822``,
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* ``statcache``, ``string``, ``TERMIOS``
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* ``mimetools``, ``MimeWriter``, ``mimify``,
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* ``mpz``, ``rgbimage``
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* Everything in lib-old: [18]_
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* Para.py, addpack.py, cmp.py, cmpcache.py, codehack.py,
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* dircmp.py, dump.py, find.py, fmt.py, grep.py, lockfile.py,
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* newdir.py, ni.py, packmail.py, poly.py, rand.py, statcache.py,
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* tb.py, tzparse.py, util.py, whatsound.py, whrandom.py, zmod.py
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* ``sys.exitfunc``: use atexit module instead [17]_
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* ``sys.exc_type``, ``sys.exc_values``, ``sys.exc_traceback``:
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not thread-safe; use ``sys.exc_info()`` or an attribute
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of the exception [2]_ [13]_ [17]_
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* ``array.read``, ``array.write`` [17]_
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* ``operator.isCallable``, ``operator.sequenceIncludes`` [17]_
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References
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==========
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.. [1] PyCon 2003 State of the Union:
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http://www.python.org/doc/essays/ppt/pycon2003/pycon2003.ppt
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.. [2] Python Regrets:
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http://www.python.org/doc/essays/ppt/regrets/PythonRegrets.pdf
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.. [3] Python Wiki:
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http://www.python.org/moin/Python3.0
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.. [4] python-dev email ("Constancy of None")
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http://mail.python.org/pipermail/python-dev/2004-July/046294.html
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.. [5] python-dev email (' "as" to be a keyword?')
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http://mail.python.org/pipermail/python-dev/2004-July/046316.html
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.. [6] python-dev email ("Comparing heterogeneous types")
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http://mail.python.org/pipermail/python-dev/2004-June/045111.html
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.. [7] python-dev email ("Let's get rid of unbound methods")
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http://mail.python.org/pipermail/python-dev/2005-January/050625.html
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.. [8] python-dev email ("Fixing _PyEval_SliceIndex so that integer-like
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objects can be used")
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http://mail.python.org/pipermail/python-dev/2005-February/051674.html
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.. [9] Guido's blog ("The fate of reduce() in Python 3000")
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http://www.artima.com/weblogs/viewpost.jsp?thread=98196
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.. [10] PEP 238 ("Changing the Division Operator")
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http://www.python.org/peps/pep-0238.html
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.. [11] Guido's blog ("Python Optional Typechecking Redux")
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http://www.artima.com/weblogs/viewpost.jsp?thread=89161
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.. [12] PEP 289 ("Generator Expressions")
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http://www.python.org/peps/pep-0289.html
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.. [13] python-dev email ("anonymous blocks")
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http://mail.python.org/pipermail/python-dev/2005-April/053060.html
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.. [14] python-dev email ("PEP 8: exception style")
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http://mail.python.org/pipermail/python-dev/2005-August/055190.html
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.. [15] python-dev email (Remove str.find in 3.0?)
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http://mail.python.org/pipermail/python-dev/2005-August/055705.html
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.. [16] python-dev email (Replacement for print in Python 3.0)
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http://mail.python.org/pipermail/python-dev/2005-September/056154.html
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.. [17] Python docs
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http://docs.python.org/ref/sequence-methods.html
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http://docs.python.org/lib/module-sys.html
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http://docs.python.org/lib/module-operator.html
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http://docs.python.org/lib/module-array.html
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http://docs.python.org/lib/bltin-file-objects.html
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.. [18] PEP 4 ("Deprecation of Standard Modules")
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http://www.python.org/peps/pep-0004.html
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.. [19] PEP 328 ("Imports: Multi-Line and Absolute/Relative")
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http://www.python.org/peps/pep-0328.html
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.. [20] PEP 352 ("Required Superclass for Exceptions")
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http://www.python.org/peps/pep-0352.html
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.. [21] python-dev email
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http://mail.python.org/pipermail/python-dev/2006-February/061169.html
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.. [22] python-dev email ("defaultdict")
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http://mail.python.org/pipermail/python-dev/2006-February/061261.html
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.. [23] PEP 308 ("Conditional Expressions")
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http://www.python.org/peps/pep-0308.html
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Copyright
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=========
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This document has been placed in the public domain.
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..
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