2009-10-11 15:31:23 -03:00
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:tocdepth: 2
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==================
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General Python FAQ
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==================
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.. contents::
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General Information
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===================
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What is Python?
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---------------
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Python is an interpreted, interactive, object-oriented programming language. It
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incorporates modules, exceptions, dynamic typing, very high level dynamic data
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types, and classes. Python combines remarkable power with very clear syntax.
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It has interfaces to many system calls and libraries, as well as to various
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window systems, and is extensible in C or C++. It is also usable as an
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extension language for applications that need a programmable interface.
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Finally, Python is portable: it runs on many Unix variants, on the Mac, and on
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PCs under MS-DOS, Windows, Windows NT, and OS/2.
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To find out more, start with :ref:`tutorial-index`. The `Beginner's Guide to
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Python <http://wiki.python.org/moin/BeginnersGuide>`_ links to other
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introductory tutorials and resources for learning Python.
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What is the Python Software Foundation?
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---------------------------------------
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The Python Software Foundation is an independent non-profit organization that
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holds the copyright on Python versions 2.1 and newer. The PSF's mission is to
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advance open source technology related to the Python programming language and to
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publicize the use of Python. The PSF's home page is at
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http://www.python.org/psf/.
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Donations to the PSF are tax-exempt in the US. If you use Python and find it
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helpful, please contribute via `the PSF donation page
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<http://www.python.org/psf/donations/>`_.
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Are there copyright restrictions on the use of Python?
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------------------------------------------------------
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You can do anything you want with the source, as long as you leave the
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copyrights in and display those copyrights in any documentation about Python
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that you produce. If you honor the copyright rules, it's OK to use Python for
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commercial use, to sell copies of Python in source or binary form (modified or
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unmodified), or to sell products that incorporate Python in some form. We would
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still like to know about all commercial use of Python, of course.
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See `the PSF license page <http://python.org/psf/license/>`_ to find further
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explanations and a link to the full text of the license.
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The Python logo is trademarked, and in certain cases permission is required to
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use it. Consult `the Trademark Usage Policy
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<http://www.python.org/psf/trademarks/>`__ for more information.
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Why was Python created in the first place?
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------------------------------------------
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Here's a *very* brief summary of what started it all, written by Guido van
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Rossum:
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I had extensive experience with implementing an interpreted language in the
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ABC group at CWI, and from working with this group I had learned a lot about
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language design. This is the origin of many Python features, including the
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use of indentation for statement grouping and the inclusion of
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very-high-level data types (although the details are all different in
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Python).
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I had a number of gripes about the ABC language, but also liked many of its
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features. It was impossible to extend the ABC language (or its
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implementation) to remedy my complaints -- in fact its lack of extensibility
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was one of its biggest problems. I had some experience with using Modula-2+
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and talked with the designers of Modula-3 and read the Modula-3 report.
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Modula-3 is the origin of the syntax and semantics used for exceptions, and
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some other Python features.
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I was working in the Amoeba distributed operating system group at CWI. We
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needed a better way to do system administration than by writing either C
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programs or Bourne shell scripts, since Amoeba had its own system call
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interface which wasn't easily accessible from the Bourne shell. My
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experience with error handling in Amoeba made me acutely aware of the
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importance of exceptions as a programming language feature.
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It occurred to me that a scripting language with a syntax like ABC but with
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access to the Amoeba system calls would fill the need. I realized that it
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would be foolish to write an Amoeba-specific language, so I decided that I
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needed a language that was generally extensible.
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During the 1989 Christmas holidays, I had a lot of time on my hand, so I
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decided to give it a try. During the next year, while still mostly working
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on it in my own time, Python was used in the Amoeba project with increasing
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success, and the feedback from colleagues made me add many early
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improvements.
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In February 1991, after just over a year of development, I decided to post to
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USENET. The rest is in the ``Misc/HISTORY`` file.
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What is Python good for?
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------------------------
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Python is a high-level general-purpose programming language that can be applied
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to many different classes of problems.
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The language comes with a large standard library that covers areas such as
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string processing (regular expressions, Unicode, calculating differences between
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files), Internet protocols (HTTP, FTP, SMTP, XML-RPC, POP, IMAP, CGI
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programming), software engineering (unit testing, logging, profiling, parsing
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Python code), and operating system interfaces (system calls, filesystems, TCP/IP
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sockets). Look at the table of contents for :ref:`library-index` to get an idea
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of what's available. A wide variety of third-party extensions are also
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available. Consult `the Python Package Index <http://pypi.python.org/pypi>`_ to
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find packages of interest to you.
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How does the Python version numbering scheme work?
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--------------------------------------------------
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Python versions are numbered A.B.C or A.B. A is the major version number -- it
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is only incremented for really major changes in the language. B is the minor
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version number, incremented for less earth-shattering changes. C is the
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micro-level -- it is incremented for each bugfix release. See :pep:`6` for more
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information about bugfix releases.
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Not all releases are bugfix releases. In the run-up to a new major release, a
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series of development releases are made, denoted as alpha, beta, or release
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candidate. Alphas are early releases in which interfaces aren't yet finalized;
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it's not unexpected to see an interface change between two alpha releases.
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Betas are more stable, preserving existing interfaces but possibly adding new
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modules, and release candidates are frozen, making no changes except as needed
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to fix critical bugs.
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Alpha, beta and release candidate versions have an additional suffix. The
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suffix for an alpha version is "aN" for some small number N, the suffix for a
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beta version is "bN" for some small number N, and the suffix for a release
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candidate version is "cN" for some small number N. In other words, all versions
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labeled 2.0aN precede the versions labeled 2.0bN, which precede versions labeled
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2.0cN, and *those* precede 2.0.
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You may also find version numbers with a "+" suffix, e.g. "2.2+". These are
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unreleased versions, built directly from the Subversion trunk. In practice,
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after a final minor release is made, the Subversion trunk is incremented to the
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next minor version, which becomes the "a0" version,
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e.g. "2.4a0".
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See also the documentation for ``sys.version``, ``sys.hexversion``, and
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``sys.version_info``.
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How do I obtain a copy of the Python source?
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--------------------------------------------
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The latest Python source distribution is always available from python.org, at
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http://www.python.org/download/. The latest development sources can be obtained
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via anonymous Subversion at http://svn.python.org/projects/python/trunk.
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The source distribution is a gzipped tar file containing the complete C source,
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Sphinx-formatted documentation, Python library modules, example programs, and
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several useful pieces of freely distributable software. The source will compile
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and run out of the box on most UNIX platforms.
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2011-10-14 13:05:56 -03:00
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Consult the `Developer FAQ <http://docs.python.org/devguide/faq>`__ for more
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information on getting the source code and compiling it.
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How do I get documentation on Python?
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-------------------------------------
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.. XXX mention py3k
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The standard documentation for the current stable version of Python is available
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at http://docs.python.org/. PDF, plain text, and downloadable HTML versions are
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also available at http://docs.python.org/download.html.
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The documentation is written in reStructuredText and processed by `the Sphinx
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documentation tool <http://sphinx.pocoo.org/>`__. The reStructuredText source
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for the documentation is part of the Python source distribution.
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I've never programmed before. Is there a Python tutorial?
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---------------------------------------------------------
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There are numerous tutorials and books available. The standard documentation
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includes :ref:`tutorial-index`.
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Consult `the Beginner's Guide <http://wiki.python.org/moin/BeginnersGuide>`_ to
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find information for beginning Python programmers, including lists of tutorials.
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Is there a newsgroup or mailing list devoted to Python?
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-------------------------------------------------------
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There is a newsgroup, :newsgroup:`comp.lang.python`, and a mailing list,
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`python-list <http://mail.python.org/mailman/listinfo/python-list>`_. The
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newsgroup and mailing list are gatewayed into each other -- if you can read news
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it's unnecessary to subscribe to the mailing list.
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:newsgroup:`comp.lang.python` is high-traffic, receiving hundreds of postings
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every day, and Usenet readers are often more able to cope with this volume.
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Announcements of new software releases and events can be found in
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comp.lang.python.announce, a low-traffic moderated list that receives about five
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postings per day. It's available as `the python-announce mailing list
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<http://mail.python.org/mailman/listinfo/python-announce-list>`_.
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More info about other mailing lists and newsgroups
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can be found at http://www.python.org/community/lists/.
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How do I get a beta test version of Python?
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-------------------------------------------
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Alpha and beta releases are available from http://www.python.org/download/. All
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releases are announced on the comp.lang.python and comp.lang.python.announce
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newsgroups and on the Python home page at http://www.python.org/; an RSS feed of
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news is available.
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You can also access the development version of Python through Subversion. See
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http://docs.python.org/devguide/faq for details.
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How do I submit bug reports and patches for Python?
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---------------------------------------------------
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To report a bug or submit a patch, please use the Roundup installation at
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http://bugs.python.org/.
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You must have a Roundup account to report bugs; this makes it possible for us to
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contact you if we have follow-up questions. It will also enable Roundup to send
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you updates as we act on your bug. If you had previously used SourceForge to
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report bugs to Python, you can obtain your Roundup password through Roundup's
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`password reset procedure <http://bugs.python.org/user?@template=forgotten>`_.
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For more information on how Python is developed, consult `the Python Developer's
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Guide <http://docs.python.org/devguide/>`_.
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Are there any published articles about Python that I can reference?
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-------------------------------------------------------------------
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It's probably best to cite your favorite book about Python.
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The very first article about Python was written in 1991 and is now quite
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outdated.
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Guido van Rossum and Jelke de Boer, "Interactively Testing Remote Servers
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Using the Python Programming Language", CWI Quarterly, Volume 4, Issue 4
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(December 1991), Amsterdam, pp 283-303.
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Are there any books on Python?
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------------------------------
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Yes, there are many, and more are being published. See the python.org wiki at
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http://wiki.python.org/moin/PythonBooks for a list.
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You can also search online bookstores for "Python" and filter out the Monty
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Python references; or perhaps search for "Python" and "language".
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Where in the world is www.python.org located?
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---------------------------------------------
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It's currently in Amsterdam, graciously hosted by `XS4ALL
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<http://www.xs4all.nl>`_. Thanks to Thomas Wouters for his work in arranging
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python.org's hosting.
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Why is it called Python?
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------------------------
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When he began implementing Python, Guido van Rossum was also reading the
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published scripts from `"Monty Python's Flying Circus"
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<http://pythonline.com/>`__, a BBC comedy series from the 1970s. Van Rossum
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thought he needed a name that was short, unique, and slightly mysterious, so he
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decided to call the language Python.
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Do I have to like "Monty Python's Flying Circus"?
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-------------------------------------------------
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No, but it helps. :)
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Python in the real world
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========================
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How stable is Python?
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---------------------
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Very stable. New, stable releases have been coming out roughly every 6 to 18
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months since 1991, and this seems likely to continue. Currently there are
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usually around 18 months between major releases.
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The developers issue "bugfix" releases of older versions, so the stability of
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existing releases gradually improves. Bugfix releases, indicated by a third
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component of the version number (e.g. 2.5.3, 2.6.2), are managed for stability;
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only fixes for known problems are included in a bugfix release, and it's
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guaranteed that interfaces will remain the same throughout a series of bugfix
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releases.
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2009-12-13 17:15:31 -04:00
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The latest stable releases can always be found on the `Python download page
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<http://python.org/download/>`_. There are two recommended production-ready
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versions at this point in time, because at the moment there are two branches of
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stable releases: 2.x and 3.x. Python 3.x may be less useful than 2.x, since
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currently there is more third party software available for Python 2 than for
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Python 3. Python 2 code will generally not run unchanged in Python 3.
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How many people are using Python?
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---------------------------------
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There are probably tens of thousands of users, though it's difficult to obtain
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an exact count.
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Python is available for free download, so there are no sales figures, and it's
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available from many different sites and packaged with many Linux distributions,
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so download statistics don't tell the whole story either.
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The comp.lang.python newsgroup is very active, but not all Python users post to
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the group or even read it.
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Have any significant projects been done in Python?
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--------------------------------------------------
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See http://python.org/about/success for a list of projects that use Python.
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Consulting the proceedings for `past Python conferences
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<http://python.org/community/workshops/>`_ will reveal contributions from many
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different companies and organizations.
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High-profile Python projects include `the Mailman mailing list manager
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<http://www.list.org>`_ and `the Zope application server
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<http://www.zope.org>`_. Several Linux distributions, most notably `Red Hat
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<http://www.redhat.com>`_, have written part or all of their installer and
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system administration software in Python. Companies that use Python internally
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include Google, Yahoo, and Lucasfilm Ltd.
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What new developments are expected for Python in the future?
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------------------------------------------------------------
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See http://www.python.org/dev/peps/ for the Python Enhancement Proposals
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(PEPs). PEPs are design documents describing a suggested new feature for Python,
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providing a concise technical specification and a rationale. Look for a PEP
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titled "Python X.Y Release Schedule", where X.Y is a version that hasn't been
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publicly released yet.
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New development is discussed on `the python-dev mailing list
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<http://mail.python.org/mailman/listinfo/python-dev/>`_.
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Is it reasonable to propose incompatible changes to Python?
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-----------------------------------------------------------
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In general, no. There are already millions of lines of Python code around the
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world, so any change in the language that invalidates more than a very small
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fraction of existing programs has to be frowned upon. Even if you can provide a
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conversion program, there's still the problem of updating all documentation;
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many books have been written about Python, and we don't want to invalidate them
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all at a single stroke.
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Providing a gradual upgrade path is necessary if a feature has to be changed.
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:pep:`5` describes the procedure followed for introducing backward-incompatible
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changes while minimizing disruption for users.
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Is Python Y2K (Year 2000) Compliant?
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------------------------------------
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.. remove this question?
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As of August, 2003 no major problems have been reported and Y2K compliance seems
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to be a non-issue.
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Python does very few date calculations and for those it does perform relies on
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the C library functions. Python generally represents times either as seconds
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since 1970 or as a ``(year, month, day, ...)`` tuple where the year is expressed
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with four digits, which makes Y2K bugs unlikely. So as long as your C library
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is okay, Python should be okay. Of course, it's possible that a particular
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application written in Python makes assumptions about 2-digit years.
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Because Python is available free of charge, there are no absolute guarantees.
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If there *are* unforeseen problems, liability is the user's problem rather than
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the developers', and there is nobody you can sue for damages. The Python
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copyright notice contains the following disclaimer:
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4. PSF is making Python 2.3 available to Licensee on an "AS IS"
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basis. PSF MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED. BY
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WAY OF EXAMPLE, BUT NOT LIMITATION, PSF MAKES NO AND DISCLAIMS ANY
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REPRESENTATION OR WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR
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PURPOSE OR THAT THE USE OF PYTHON 2.3 WILL NOT INFRINGE ANY THIRD PARTY
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RIGHTS.
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5. PSF SHALL NOT BE LIABLE TO LICENSEE OR ANY OTHER USERS OF PYTHON
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2.3 FOR ANY INCIDENTAL, SPECIAL, OR CONSEQUENTIAL DAMAGES OR LOSS AS
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A RESULT OF MODIFYING, DISTRIBUTING, OR OTHERWISE USING PYTHON 2.3,
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OR ANY DERIVATIVE THEREOF, EVEN IF ADVISED OF THE POSSIBILITY THEREOF.
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The good news is that *if* you encounter a problem, you have full source
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available to track it down and fix it. This is one advantage of an open source
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programming environment.
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Is Python a good language for beginning programmers?
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----------------------------------------------------
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Yes.
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It is still common to start students with a procedural and statically typed
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language such as Pascal, C, or a subset of C++ or Java. Students may be better
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served by learning Python as their first language. Python has a very simple and
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consistent syntax and a large standard library and, most importantly, using
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Python in a beginning programming course lets students concentrate on important
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programming skills such as problem decomposition and data type design. With
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Python, students can be quickly introduced to basic concepts such as loops and
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procedures. They can probably even work with user-defined objects in their very
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first course.
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For a student who has never programmed before, using a statically typed language
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seems unnatural. It presents additional complexity that the student must master
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and slows the pace of the course. The students are trying to learn to think
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like a computer, decompose problems, design consistent interfaces, and
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encapsulate data. While learning to use a statically typed language is
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important in the long term, it is not necessarily the best topic to address in
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the students' first programming course.
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Many other aspects of Python make it a good first language. Like Java, Python
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has a large standard library so that students can be assigned programming
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projects very early in the course that *do* something. Assignments aren't
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restricted to the standard four-function calculator and check balancing
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programs. By using the standard library, students can gain the satisfaction of
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working on realistic applications as they learn the fundamentals of programming.
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Using the standard library also teaches students about code reuse. Third-party
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modules such as PyGame are also helpful in extending the students' reach.
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Python's interactive interpreter enables students to test language features
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while they're programming. They can keep a window with the interpreter running
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while they enter their program's source in another window. If they can't
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remember the methods for a list, they can do something like this::
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>>> L = []
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>>> dir(L)
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['append', 'count', 'extend', 'index', 'insert', 'pop', 'remove',
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'reverse', 'sort']
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>>> help(L.append)
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Help on built-in function append:
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append(...)
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L.append(object) -- append object to end
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>>> L.append(1)
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>>> L
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[1]
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With the interpreter, documentation is never far from the student as he's
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programming.
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There are also good IDEs for Python. IDLE is a cross-platform IDE for Python
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that is written in Python using Tkinter. PythonWin is a Windows-specific IDE.
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Emacs users will be happy to know that there is a very good Python mode for
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Emacs. All of these programming environments provide syntax highlighting,
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auto-indenting, and access to the interactive interpreter while coding. Consult
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http://www.python.org/editors/ for a full list of Python editing environments.
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If you want to discuss Python's use in education, you may be interested in
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|
joining `the edu-sig mailing list
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<http://python.org/community/sigs/current/edu-sig>`_.
|
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|
Upgrading Python
|
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|
|
================
|
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|
|
|
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|
What is this bsddb185 module my application keeps complaining about?
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|
--------------------------------------------------------------------
|
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|
|
|
|
|
|
.. XXX remove this question?
|
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|
|
|
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|
|
Starting with Python2.3, the distribution includes the `PyBSDDB package
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<http://pybsddb.sf.net/>` as a replacement for the old bsddb module. It
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includes functions which provide backward compatibility at the API level, but
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|
requires a newer version of the underlying `Berkeley DB
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|
<http://www.sleepycat.com>`_ library. Files created with the older bsddb module
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can't be opened directly using the new module.
|
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Using your old version of Python and a pair of scripts which are part of Python
|
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|
|
2.3 (db2pickle.py and pickle2db.py, in the Tools/scripts directory) you can
|
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|
|
convert your old database files to the new format. Using your old Python
|
|
|
|
version, run the db2pickle.py script to convert it to a pickle, e.g.::
|
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|
python2.2 <pathto>/db2pickley.py database.db database.pck
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Rename your database file::
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|
mv database.db olddatabase.db
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Now convert the pickle file to a new format database::
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|
python <pathto>/pickle2db.py database.db database.pck
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|
The precise commands you use will vary depending on the particulars of your
|
|
|
|
installation. For full details about operation of these two scripts check the
|
|
|
|
doc string at the start of each one.
|