What's New in Python 3.0
****************************
+.. XXX add trademark info for Apple, Microsoft, SourceForge.
+
:Author: Guido van Rossum
-:Release: 0.1
+:Release: |release|
+:Date: |today|
-.. Rules for maintenance:
+.. $Id$
+ Rules for maintenance:
* Anyone can add text to this document. Do not spend very much time
on the wording of your changes, because your text will probably
This saves the maintainer the effort of going through the SVN log
when researching a change.
-This article explains the new features in Python 3.0, comparing to 2.6
-(or in some cases 2.5, since 2.6 isn't released yet).
-
-The best estimate for a release date is August 2008.
+This article explains the new features in Python 3.0, comparing to 2.6.
+In some cases it will also summarize changes since 2.5, with a reference
+to "What's New in Python 2.6" for the details. Python 2.6 was released
+on October 1 2008. Python 3.0 will be released in December 2008.
This article doesn't attempt to provide a complete specification of
the new features, but instead provides a convenient overview. For
that if a file is opened using an incorrect mode or encoding, I/O
will likely fail.
+* The ordering comparison operators (``<``, ``<=``, ``>=``, ``>``)
+ raise a TypeError exception when the operands don't have a
+ meaningful natural ordering. Thus, expressions like ``1 < ''``, ``0
+ > None`` or ``len < len`` are no longer valid. A corollary is that
+ sorting a heterogeneous list no longer makes sense -- all the
+ elements must be comparable to each other. Note that this does not
+ apply to the ``==`` and ``!=`` operators: objects of different
+ uncomparable types always compare unequal to each other, and an
+ object always compares equal to itself (i.e., ``x is y`` implies ``x
+ = y``; this is true even for ``NaN``).
+
* :func:`map` and :func:`filter` return iterators. A quick fix is e.g.
``list(map(...))``, but a better fix is often to use a list
comprehension (especially when the original code uses :keyword:`lambda`).
* ``1/2`` returns a float. Use ``1//2`` to get the truncating behavior.
+.. XXX move the next one to a later point, it's not a common stumbling block.
+
* The :func:`repr` of a long integer doesn't include the trailing ``L``
anymore, so code that unconditionally strips that character will
chop off the last digit instead.
or :meth:`bytes.decode` (bytes -> str) methods.
* All backslashes in raw strings are interpreted literally. This means that
- Unicode escapes are not treated specially.
+ ``'\U'`` and ``'\u'`` escapes in raw strings are not treated specially.
.. XXX add bytearray
* The :mod:`StringIO` and :mod:`cStringIO` modules are gone. Instead, import
:class:`io.StringIO` or :class:`io.BytesIO`.
-* ``'\U'`` and ``'\u'`` escapes in raw strings are not treated specially.
PEP 3101: A New Approach to String Formatting
=============================================
-.. XXX expand this
+* A new system for built-in string formatting operations replaces the
+ ``%`` string formatting operator. (However, the ``%`` operator is
+ still supported; it will be deprecated in Python 3.1 and removed
+ from the language at some later time.)
-* A new system for built-in string formatting operations replaces the ``%``
- string formatting operator.
+.. XXX expand this
PEP 3106: Revamping dict :meth:`dict.keys`, :meth:`dict.items` and :meth:`dict.values`
methods have been removed.
* :meth:`dict.keys`, :meth:`dict.values` and :meth:`dict.items` return objects
- with set behavior that reference the underlying dict.
+ with set behavior that reference the underlying dict; these are often
+ referred to as *dictionary views*.
PEP 3107: Function Annotations
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