
General Python FAQ
******************


General Information
===================


What is Python?
---------------

Python is an interpreted, interactive, object-oriented programming
language.  It incorporates modules, exceptions, dynamic typing, very
high level dynamic data types, and classes.  Python combines
remarkable power with very clear syntax. It has interfaces to many
system calls and libraries, as well as to various window systems, and
is extensible in C or C++.  It is also usable as an extension language
for applications that need a programmable interface. Finally, Python
is portable: it runs on many Unix variants, on the Mac, and on PCs
under MS-DOS, Windows, Windows NT, and OS/2.

To find out more, start with *The Python Tutorial*.  The Beginner's
Guide to Python links to other introductory tutorials and resources
for learning Python.


What is the Python Software Foundation?
---------------------------------------

The Python Software Foundation is an independent non-profit
organization that holds the copyright on Python versions 2.1 and
newer.  The PSF's mission is to advance open source technology related
to the Python programming language and to publicize the use of Python.
The PSF's home page is at http://www.python.org/psf/.

Donations to the PSF are tax-exempt in the US.  If you use Python and
find it helpful, please contribute via the PSF donation page.


Are there copyright restrictions on the use of Python?
------------------------------------------------------

You can do anything you want with the source, as long as you leave the
copyrights in and display those copyrights in any documentation about
Python that you produce.  If you honor the copyright rules, it's OK to
use Python for commercial use, to sell copies of Python in source or
binary form (modified or unmodified), or to sell products that
incorporate Python in some form.  We would still like to know about
all commercial use of Python, of course.

See the PSF license page to find further explanations and a link to
the full text of the license.

The Python logo is trademarked, and in certain cases permission is
required to use it.  Consult the Trademark Usage Policy for more
information.


Why was Python created in the first place?
------------------------------------------

Here's a *very* brief summary of what started it all, written by Guido
van Rossum:

   I had extensive experience with implementing an interpreted
   language in the ABC group at CWI, and from working with this group
   I had learned a lot about language design.  This is the origin of
   many Python features, including the use of indentation for
   statement grouping and the inclusion of very-high-level data types
   (although the details are all different in Python).

   I had a number of gripes about the ABC language, but also liked
   many of its features.  It was impossible to extend the ABC language
   (or its implementation) to remedy my complaints -- in fact its lack
   of extensibility was one of its biggest problems.  I had some
   experience with using Modula-2+ and talked with the designers of
   Modula-3 and read the Modula-3 report. Modula-3 is the origin of
   the syntax and semantics used for exceptions, and some other Python
   features.

   I was working in the Amoeba distributed operating system group at
   CWI.  We needed a better way to do system administration than by
   writing either C programs or Bourne shell scripts, since Amoeba had
   its own system call interface which wasn't easily accessible from
   the Bourne shell.  My experience with error handling in Amoeba made
   me acutely aware of the importance of exceptions as a programming
   language feature.

   It occurred to me that a scripting language with a syntax like ABC
   but with access to the Amoeba system calls would fill the need.  I
   realized that it would be foolish to write an Amoeba-specific
   language, so I decided that I needed a language that was generally
   extensible.

   During the 1989 Christmas holidays, I had a lot of time on my hand,
   so I decided to give it a try.  During the next year, while still
   mostly working on it in my own time, Python was used in the Amoeba
   project with increasing success, and the feedback from colleagues
   made me add many early improvements.

   In February 1991, after just over a year of development, I decided
   to post to USENET.  The rest is in the ``Misc/HISTORY`` file.


What is Python good for?
------------------------

Python is a high-level general-purpose programming language that can
be applied to many different classes of problems.

The language comes with a large standard library that covers areas
such as string processing (regular expressions, Unicode, calculating
differences between files), Internet protocols (HTTP, FTP, SMTP, XML-
RPC, POP, IMAP, CGI programming), software engineering (unit testing,
logging, profiling, parsing Python code), and operating system
interfaces (system calls, filesystems, TCP/IP sockets).  Look at the
table of contents for *The Python Standard Library* to get an idea of
what's available.  A wide variety of third-party extensions are also
available.  Consult the Python Package Index to find packages of
interest to you.


How does the Python version numbering scheme work?
--------------------------------------------------

Python versions are numbered A.B.C or A.B.  A is the major version
number -- it is only incremented for really major changes in the
language.  B is the minor version number, incremented for less earth-
shattering changes.  C is the micro-level -- it is incremented for
each bugfix release.  See **PEP 6** for more information about bugfix
releases.

Not all releases are bugfix releases.  In the run-up to a new major
release, a series of development releases are made, denoted as alpha,
beta, or release candidate.  Alphas are early releases in which
interfaces aren't yet finalized; it's not unexpected to see an
interface change between two alpha releases. Betas are more stable,
preserving existing interfaces but possibly adding new modules, and
release candidates are frozen, making no changes except as needed to
fix critical bugs.

Alpha, beta and release candidate versions have an additional suffix.
The suffix for an alpha version is "aN" for some small number N, the
suffix for a beta version is "bN" for some small number N, and the
suffix for a release candidate version is "cN" for some small number
N.  In other words, all versions labeled 2.0aN precede the versions
labeled 2.0bN, which precede versions labeled 2.0cN, and *those*
precede 2.0.

You may also find version numbers with a "+" suffix, e.g. "2.2+".
These are unreleased versions, built directly from the Subversion
trunk.  In practice, after a final minor release is made, the
Subversion trunk is incremented to the next minor version, which
becomes the "a0" version, e.g. "2.4a0".

See also the documentation for ``sys.version``, ``sys.hexversion``,
and ``sys.version_info``.


How do I obtain a copy of the Python source?
--------------------------------------------

The latest Python source distribution is always available from
python.org, at http://www.python.org/download/.  The latest
development sources can be obtained via anonymous Mercurial access at
http://hg.python.org/cpython.

The source distribution is a gzipped tar file containing the complete
C source, Sphinx-formatted documentation, Python library modules,
example programs, and several useful pieces of freely distributable
software.  The source will compile and run out of the box on most UNIX
platforms.

Consult the Developer FAQ for more information on getting the source
code and compiling it.


How do I get documentation on Python?
-------------------------------------

The standard documentation for the current stable version of Python is
available at http://docs.python.org/.  PDF, plain text, and
downloadable HTML versions are also available at
http://docs.python.org/download.html.

The documentation is written in reStructuredText and processed by the
Sphinx documentation tool.  The reStructuredText source for the
documentation is part of the Python source distribution.


I've never programmed before. Is there a Python tutorial?
---------------------------------------------------------

There are numerous tutorials and books available.  The standard
documentation includes *The Python Tutorial*.

Consult the Beginner's Guide to find information for beginning Python
programmers, including lists of tutorials.


Is there a newsgroup or mailing list devoted to Python?
-------------------------------------------------------

There is a newsgroup, *comp.lang.python*, and a mailing list, python-
list.  The newsgroup and mailing list are gatewayed into each other --
if you can read news it's unnecessary to subscribe to the mailing
list. *comp.lang.python* is high-traffic, receiving hundreds of
postings every day, and Usenet readers are often more able to cope
with this volume.

Announcements of new software releases and events can be found in
comp.lang.python.announce, a low-traffic moderated list that receives
about five postings per day.  It's available as the python-announce
mailing list.

More info about other mailing lists and newsgroups can be found at
http://www.python.org/community/lists/.


How do I get a beta test version of Python?
-------------------------------------------

Alpha and beta releases are available from
http://www.python.org/download/.  All releases are announced on the
comp.lang.python and comp.lang.python.announce newsgroups and on the
Python home page at http://www.python.org/; an RSS feed of news is
available.

You can also access the development version of Python through
Subversion.  See http://docs.python.org/devguide/faq for details.


How do I submit bug reports and patches for Python?
---------------------------------------------------

To report a bug or submit a patch, please use the Roundup installation
at http://bugs.python.org/.

You must have a Roundup account to report bugs; this makes it possible
for us to contact you if we have follow-up questions.  It will also
enable Roundup to send you updates as we act on your bug. If you had
previously used SourceForge to report bugs to Python, you can obtain
your Roundup password through Roundup's password reset procedure.

For more information on how Python is developed, consult the Python
Developer's Guide.


Are there any published articles about Python that I can reference?
-------------------------------------------------------------------

It's probably best to cite your favorite book about Python.

The very first article about Python was written in 1991 and is now
quite outdated.

   Guido van Rossum and Jelke de Boer, "Interactively Testing Remote
   Servers Using the Python Programming Language", CWI Quarterly,
   Volume 4, Issue 4 (December 1991), Amsterdam, pp 283-303.


Are there any books on Python?
------------------------------

Yes, there are many, and more are being published.  See the python.org
wiki at http://wiki.python.org/moin/PythonBooks for a list.

You can also search online bookstores for "Python" and filter out the
Monty Python references; or perhaps search for "Python" and
"language".


Where in the world is www.python.org located?
---------------------------------------------

It's currently in Amsterdam, graciously hosted by XS4ALL.  Thanks to
Thomas Wouters for his work in arranging python.org's hosting.


Why is it called Python?
------------------------

When he began implementing Python, Guido van Rossum was also reading
the published scripts from "Monty Python's Flying Circus", a BBC
comedy series from the 1970s.  Van Rossum thought he needed a name
that was short, unique, and slightly mysterious, so he decided to call
the language Python.


Do I have to like "Monty Python's Flying Circus"?
-------------------------------------------------

No, but it helps.  :)


Python in the real world
========================


How stable is Python?
---------------------

Very stable.  New, stable releases have been coming out roughly every
6 to 18 months since 1991, and this seems likely to continue.
Currently there are usually around 18 months between major releases.

The developers issue "bugfix" releases of older versions, so the
stability of existing releases gradually improves.  Bugfix releases,
indicated by a third component of the version number (e.g. 2.5.3,
2.6.2), are managed for stability; only fixes for known problems are
included in a bugfix release, and it's guaranteed that interfaces will
remain the same throughout a series of bugfix releases.

The latest stable releases can always be found on the Python download
page.  There are two recommended production-ready versions at this
point in time, because at the moment there are two branches of stable
releases: 2.x and 3.x.  Python 3.x may be less useful than 2.x, since
currently there is more third party software available for Python 2
than for Python 3.  Python 2 code will generally not run unchanged in
Python 3.


How many people are using Python?
---------------------------------

There are probably tens of thousands of users, though it's difficult
to obtain an exact count.

Python is available for free download, so there are no sales figures,
and it's available from many different sites and packaged with many
Linux distributions, so download statistics don't tell the whole story
either.

The comp.lang.python newsgroup is very active, but not all Python
users post to the group or even read it.


Have any significant projects been done in Python?
--------------------------------------------------

See http://python.org/about/success for a list of projects that use
Python. Consulting the proceedings for past Python conferences will
reveal contributions from many different companies and organizations.

High-profile Python projects include the Mailman mailing list manager
and the Zope application server.  Several Linux distributions, most
notably Red Hat, have written part or all of their installer and
system administration software in Python.  Companies that use Python
internally include Google, Yahoo, and Lucasfilm Ltd.


What new developments are expected for Python in the future?
------------------------------------------------------------

See http://www.python.org/dev/peps/ for the Python Enhancement
Proposals (PEPs). PEPs are design documents describing a suggested new
feature for Python, providing a concise technical specification and a
rationale.  Look for a PEP titled "Python X.Y Release Schedule", where
X.Y is a version that hasn't been publicly released yet.

New development is discussed on the python-dev mailing list.


Is it reasonable to propose incompatible changes to Python?
-----------------------------------------------------------

In general, no.  There are already millions of lines of Python code
around the world, so any change in the language that invalidates more
than a very small fraction of existing programs has to be frowned
upon.  Even if you can provide a conversion program, there's still the
problem of updating all documentation; many books have been written
about Python, and we don't want to invalidate them all at a single
stroke.

Providing a gradual upgrade path is necessary if a feature has to be
changed. **PEP 5** describes the procedure followed for introducing
backward-incompatible changes while minimizing disruption for users.


Is Python Y2K (Year 2000) Compliant?
------------------------------------

As of August, 2003 no major problems have been reported and Y2K
compliance seems to be a non-issue.

Python does very few date calculations and for those it does perform
relies on the C library functions.  Python generally represents times
either as seconds since 1970 or as a ``(year, month, day, ...)`` tuple
where the year is expressed with four digits, which makes Y2K bugs
unlikely.  So as long as your C library is okay, Python should be
okay.  Of course, it's possible that a particular application written
in Python makes assumptions about 2-digit years.

Because Python is available free of charge, there are no absolute
guarantees. If there *are* unforeseen problems, liability is the
user's problem rather than the developers', and there is nobody you
can sue for damages.  The Python copyright notice contains the
following disclaimer:

   4. PSF is making Python 2.3 available to Licensee on an "AS IS"
   basis.  PSF MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR
   IMPLIED.  BY WAY OF EXAMPLE, BUT NOT LIMITATION, PSF MAKES NO AND
   DISCLAIMS ANY REPRESENTATION OR WARRANTY OF MERCHANTABILITY OR
   FITNESS FOR ANY PARTICULAR PURPOSE OR THAT THE USE OF PYTHON 2.3
   WILL NOT INFRINGE ANY THIRD PARTY RIGHTS.

   5. PSF SHALL NOT BE LIABLE TO LICENSEE OR ANY OTHER USERS OF PYTHON
   2.3 FOR ANY INCIDENTAL, SPECIAL, OR CONSEQUENTIAL DAMAGES OR LOSS
   AS A RESULT OF MODIFYING, DISTRIBUTING, OR OTHERWISE USING PYTHON
   2.3, OR ANY DERIVATIVE THEREOF, EVEN IF ADVISED OF THE POSSIBILITY
   THEREOF.

The good news is that *if* you encounter a problem, you have full
source available to track it down and fix it.  This is one advantage
of an open source programming environment.


Is Python a good language for beginning programmers?
----------------------------------------------------

Yes.

It is still common to start students with a procedural and statically
typed language such as Pascal, C, or a subset of C++ or Java.
Students may be better served by learning Python as their first
language.  Python has a very simple and consistent syntax and a large
standard library and, most importantly, using Python in a beginning
programming course lets students concentrate on important programming
skills such as problem decomposition and data type design.  With
Python, students can be quickly introduced to basic concepts such as
loops and procedures.  They can probably even work with user-defined
objects in their very first course.

For a student who has never programmed before, using a statically
typed language seems unnatural.  It presents additional complexity
that the student must master and slows the pace of the course.  The
students are trying to learn to think like a computer, decompose
problems, design consistent interfaces, and encapsulate data.  While
learning to use a statically typed language is important in the long
term, it is not necessarily the best topic to address in the students'
first programming course.

Many other aspects of Python make it a good first language.  Like
Java, Python has a large standard library so that students can be
assigned programming projects very early in the course that *do*
something.  Assignments aren't restricted to the standard four-
function calculator and check balancing programs.  By using the
standard library, students can gain the satisfaction of working on
realistic applications as they learn the fundamentals of programming.
Using the standard library also teaches students about code reuse.
Third-party modules such as PyGame are also helpful in extending the
students' reach.

Python's interactive interpreter enables students to test language
features while they're programming.  They can keep a window with the
interpreter running while they enter their program's source in another
window.  If they can't remember the methods for a list, they can do
something like this:

   >>> L = []
   >>> dir(L)
   ['append', 'count', 'extend', 'index', 'insert', 'pop', 'remove',
   'reverse', 'sort']
   >>> help(L.append)
   Help on built-in function append:

   append(...)
       L.append(object) -- append object to end
   >>> L.append(1)
   >>> L
   [1]

With the interpreter, documentation is never far from the student as
he's programming.

There are also good IDEs for Python.  IDLE is a cross-platform IDE for
Python that is written in Python using Tkinter.  PythonWin is a
Windows-specific IDE. Emacs users will be happy to know that there is
a very good Python mode for Emacs.  All of these programming
environments provide syntax highlighting, auto-indenting, and access
to the interactive interpreter while coding.  Consult
http://www.python.org/editors/ for a full list of Python editing
environments.

If you want to discuss Python's use in education, you may be
interested in joining the edu-sig mailing list.


Upgrading Python
================


What is this bsddb185 module my application keeps complaining about?
--------------------------------------------------------------------

Starting with Python2.3, the distribution includes the *PyBSDDB
package <http://pybsddb.sf.net/>* as a replacement for the old bsddb
module.  It includes functions which provide backward compatibility at
the API level, but requires a newer version of the underlying Berkeley
DB library.  Files created with the older bsddb module can't be opened
directly using the new module.

Using your old version of Python and a pair of scripts which are part
of Python 2.3 (db2pickle.py and pickle2db.py, in the Tools/scripts
directory) you can 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.:

   python2.2 <pathto>/db2pickley.py database.db database.pck

Rename your database file:

   mv database.db olddatabase.db

Now convert the pickle file to a new format database:

   python <pathto>/pickle2db.py database.db database.pck

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.
