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several new questions, 1.3 beta mentioned

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Guido van Rossum 1995-08-28 19:41:35 +00:00
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@ -3,14 +3,14 @@ Newsgroups: comp.lang.python,comp.answers,news.answers
Followup-to: comp.lang.python
From: guido@cwi.nl (Guido van Rossum)
Reply-to: guido@cnri.reston.va.us (Guido van Rossum)
Expires: Fri, 1 Sep 1995 00:00:00 GMT
Expires: Sun, 1 Oct 1995 00:00:00 GMT
Supersedes: <DCA29p.A9A@cwi.nl>
Approved: news-answers-request@MIT.Edu
Archive-name: python-faq/part1
Submitted-by: Guido van Rossum <guido@cwi.nl>
Version: 1.25++
Last-modified: 25 July 1995
Version: 1.27
Last-modified: 28 August 1995
This article contains answers to Frequently Asked Questions about
Python (an object-oriented interpreted programming language -- see
@ -21,13 +21,12 @@ redistribution of this FAQ is allowed. Printed redistribution only
with permission of the author. No warranties.
Author's address:
Guido van Rossum
CWI, dept. CST
Kruislaan 413
P.O. Box 94079
1090 GB Amsterdam
The Netherlands
Email: <guido@cwi.nl>
Guido van Rossum
C.N.R.I.
1895 Preston White Drive
Reston, VA 22091
U.S.A.
Email: <guido@python.org>, <guido@cnri.reston.va.us>, <guido@cwi.nl>
The latest version of this FAQ is available by anonymous ftp from
<URL:ftp://ftp.python.org/pub/python/FAQ>. It will also be posted
@ -49,7 +48,7 @@ This FAQ is divided in the following chapters:
1. General information and availability
2. Python in the real world
3. Building Python
3. Building Python and Other Known Bugs
4. Programming in Python
5. Extending Python
6. Python's design
@ -89,8 +88,9 @@ Here's an overview of the questions per chapter:
2.5. Q. When will the next version be released?
2.6. Q. What new developments are expected for Python in the future?
2.7. Q. Is it reasonable to propose incompatible changes to Python?
2.8. Q. What is the future of Python?
3. Building Python
3. Building Python and Other Known Bugs
3.1. Q. Is there a test set?
3.2. Q. When running the test set, I get complaints about floating point
operations, but when playing with floating point operations I cannot
@ -110,6 +110,10 @@ Here's an overview of the questions per chapter:
3.13. Q. How to configure dynamic loading on Lixux.
3.14. Q. Under Solaris 2.x, using GCC, how do I use shared libraries?
3.15. Q. Errors when linking with a shared library containing C++ code.
3.16. Q. Tk menus don't work properly in Python 1.2
3.17. Q. I built with tkintermodule.c enabled but get "Tkinter not found"
3.18. Q. I built with Tk 4.0 but Tkinter complains about the Tk version
3.19. Q. Tk doesn't work right on DEC Alpha
4. Programming in Python
4.1. Q. Is there a source code level debugger with breakpoints, step,
@ -176,10 +180,10 @@ Here's an overview of the questions per chapter:
5.8. Q. How do I call an object's method from C?
5.9. Q. How do I catch the output from print_error()?
5.10. Q. How do I access a module written in Python from C?
5.11. Q. How do I interface to C++ objects from Python?
6. Python's design
6.1. Q. Why isn't there a generic copying operation for objects in
Python?
6.1. Q. Why isn't there a generic copying operation for objects in Python?
6.2. Q. Why isn't there a generic way to implement persistent objects
in Python? (Persistent == automatically saved to and restored from
disk.)
@ -199,6 +203,7 @@ Here's an overview of the questions per chapter:
6.11. Q. Why can't lambda forms contain statements?
6.12. Q. Why is there no more efficient way of iterating over a dictionary
than first constructing the list of keys()?
6.13. Q. Can Python be compiled to machine code, C or some other language?
7. Using Python on non-UNIX platforms
7.1. Q. Is there a Mac version of Python?
@ -225,7 +230,7 @@ question 4.2 in vi, type /^4\.2\. Q/).
1. General information and availability
=======================================
=======================================
1.1. Q. What is Python?
@ -294,7 +299,7 @@ site).
A. The following anonymous ftp sites keep mirrors of the Python
distribution:
<URL:ftp://ftp.cwi.nl/pub/python/>
<URL:ftp://ftp.cwi.nl/pub/python/>
<URL:ftp://gatekeeper.dec.com/pub/plan/python/>
<URL:ftp://ftp.uu.net/languages/python/>
<URL:ftp://ftp.wustl.edu/graphics/graphics/sgi-stuff/python/>
@ -302,7 +307,7 @@ distribution:
<URL:ftp://ftp.sunet.se/pub/lang/python/>
<URL:ftp://unix.hensa.ac.uk/mirrors/uunet/languages/python/>
<URL:ftp://ftp.sterling.com/programming/languages/python/>
<URL:ftp://ftp.ibp.fr/pub/python/>
<URL:ftp://ftp.ibp.fr/pub/python/>
<URL:ftp://ftp.switch.ch/software/sources/python/>
<URL:ftp://ftp.informatik.tu-muenchen.de/pub/comp/programming/languages/python/>
@ -484,6 +489,10 @@ on the net since then.
Missing-him-too-ly yours...
PS: support for Python's Emacs mode (Misc/python-mode.el in the
distribution) has been taken up by Barry Warsaw. Questions about it
should be mailed to <python-mode@python.org>.
2. Python in the real world
===========================
@ -499,6 +508,9 @@ is even less meaningful. I see new names on the newsgroup all the
time and my best guess is that there are currently at least several
thousands of users.
Another statistic is the number of accesses to the Python WWW server.
Have a look at <URL:http://www.python.org/stats/>.
2.2. Q. Have any significant projects been done in Python?
A. Here at CWI (the home of Python), we have written a 20,000 line
@ -516,6 +528,8 @@ The University of California, Irvine uses a student administration
system called TELE-Vision written entirely in Python. Contact: Ray
Price <rlprice@uci.edu>.
See also the next question.
If you have done a significant project in Python that you'd like to be
included in the list above, send me email!
@ -549,6 +563,13 @@ Individuals at many other companies are using Python for internal
development or for as yet unannounced products (witness their
contributions to the Python mailing list or newsgroup).
SGI has advertised in the Python list looking for Python programmers
for a project involving interactive television.
See also the workshop minutes at
<URL:http://www.python.org/workshops/> -- in general the WWW server is
more up to date than the FAQ for these issues.
Python has also been elected as an extension language by MADE, a
consortium supported by the European Committee's ESPRIT program and
consisting of Bull, CWI and some other European companies. Contact:
@ -565,16 +586,17 @@ in the early stages of development, in fact new, stable releases
2.5. Q. When will the next version be released?
A. I am planning to release 1.3 in September or early October 1995.
It will contain keyword parameters as the most important new language
feature. Beta versions may be available as early as August.
A. I am planning to release 1.3 in early October 1995. It will
contain keyword parameters as the most important new language feature.
A beta version was made available in August, more beta versions may
appear.
2.6. Q. What new developments are expected for Python in the future?
A. See my Work-In-Progress web page, currently at
<URL:http://www.python.org:~guido/WIP.html>, and the pages for the
Second Python Workshop (best reached via the Python home page,
<URL:http://www.python.org/>).
<URL:http://www.python.org/>). Also follow the newsgroup discussions!
2.7. Q. Is it reasonable to propose incompatible changes to Python?
@ -585,9 +607,28 @@ upon. Even if you can provide a conversion program, there still is
the problem of updating all documentation. Providing a gradual
upgrade path is the only way if a feature has to be changed.
2.8. Q. What is the future of Python?
3. Building Python
==================
A. If I knew, I'd be rich :-)
Seriously, the formation of the PSA (Pyton Software Activity, see
<URL:http://www.python.org/psa/>) ensures some kind of support even in
the (unlikely! event that I'd be hit by a bus (actually, here in the
US, a car accident would be more likely :-), were to join a nunnery,
or would be head-hunted. A large number of Python users have become
experts at Python programming as well as maintenance of the
implementation, and would easily fill the vacuum created by my
disappearance.
In the mean time, I have no plans to disappear -- rather, I am
committed to improving Python, and my current benefactor, CNRI (see
<URL:http://www.cnri.reston.va.us>) is just as committed to continue
its support of Python and the PSA. In fact, we have great plans for
Python -- we just can't tell yet!
3. Building Python and Other Known Bugs
=======================================
3.1. Q. Is there a test set?
@ -797,6 +838,42 @@ A. Link the main Python binary with C++. Change the definition of
LINKCC in Modules/Makefile to be your C++ compiler. You may have to
edit config.c slightly to make it compilable with C++.
3.16. Q. Tk menus don't work properly in Python 1.2.
A. There's a bug in Tkinter.py; remove ClassType and InstanceType from
the definition of CallableTypes near the top of Lib/tkinter/Tkinter.py.
3.17. Q. I built with tkintermodule.c enabled but get "Tkinter not found".
A. Tkinter.py (note: upper case T) lives in a subdirectory of Lib,
Lib/tkinter. If you are using the default module search path, you
probably didn't enable the line in the Modules/Setup file defining
TKPATH; if you use the environment variable PYTHONPATH, you'll have to
add the proper tkinter subdirectory.
3.18. Q. I built with Tk 4.0 but Tkinter complains about the Tk version.
A. Several things could cause this. You most likely have a Tk 3.6
installation that wasn't completely eradicated by the Tk 4.0
installation (which tends to add "4.0" to its installed files). You
may have the Tk 3.6 support library installed in the place where the
Tk 4.0 support files should be (default /usr/local/lib/tk/); you may
have compiled Python with the old tk.h header file (yes, this actually
compiles!); you may actually have linked with Tk 3.6 even though Tk
4.0 is also around. Similar for Tcl 7.4 vs. Tcl 7.3.
3.19. Q. Tk doesn't work right on DEC Alpha.
A. You probably compiled either Tcl, Tk or Python with gcc. Don't.
For this platform, which has 64-bit integers, gcc is known to generate
broken code. The standard cc (which comes bundled with the OS!)
works. If you still prefer gcc, at least try recompiling with cc
before reporting problems to the newsgroup or the author; if this
fixes the problem, report the bug to the gcc developers instead. (As
far as we know, there are no problem with gcc on other platforms --
the instabilities seem to be restricted to the DEC Alpha.) See also
question 3.6.
4. Programming in Python
========================
@ -1598,33 +1675,59 @@ the module) as follows:
Calling setattr(), to assign to variables in the module, also works.
5.11. Q. How do I interface to C++ objects from Python?
A. Depending on your requirements, there are many approaches. Begin
by reading the "Extending and Embedding" document (Doc/ext.tex, see
also <URL:http://www.python.org/doc/>). Realize that for the Python
run-time system, there isn't a whole lot of difference between C and
C++ -- so the strategy to build a new Python type around a C structure
(pointer) type will also work for C++ objects.
Automatic generation of interfaces between Python and C++ is still at
the horizon -- parsing C++ header files requires an almost complete
C++ parser, and many features aren't easily translated from C++ to
Python: certain forms of operator oveloading, function overloading
(best approached by a varargs function which explicitly type-checks
its arguments), and reference arguments are just a number of features
that are hard to translate correctly if at all.
The hardest problem is to transparently translate the C++ class
hierarchy to Python, so that Python programs derive classes from C++
classes. Given suitable constraints, this may be possible, but it
would require more space than I have in this FAQ to explain how.
In any case, you can get quite a bit done without this, using just the
existing classes from Python.
If this all seems rather daunting, that may be because it is -- C++
isn't exactly a baby to handle without gloves! However, people have
accomplished amazing feats of interfacing between Python and C++, and
a detailed question posted to the Python list is likely to elicit some
interesting and useful responses.
6. Python's design
==================
6.1. Q. Why isn't there a generic copying operation for objects in
Python?
6.1. Q. Why isn't there a generic copying operation for objects in Python?
A. Hmm. Maybe there should be one, but it's difficult to assign a
useful meaning to copying of open files, sockets and windows, or
recursive data structures. As long as you design all your classes
yourself you are of course free to define a standard base class that
defines an overridable copying operation for all the objects you care
about. (One practical point: it would have to be a built-in function,
not a standard method name, since not all built-in object types have
methods; e.g. strings, integers and tuples don't.)
A. Historically, there wasn't. However, starting in Python 1.2,
there's a library module "copy" which supports both shallow and deep
copying of most common Python objects (though not things like open
files, sockets or windows), including an extensible mechanism to copy
class instances.
6.2. Q. Why isn't there a generic way to implement persistent objects
in Python? (Persistent == automatically saved to and restored from
disk.)
A. Hmm, hmm. Basically for the same reasons as why there is no
generic copying operation.
A partial solution will appear in release 1.2. This will also provide
a partial solution to the problem of a generic copying operation.
(Partial because it still won't cope with open files etc.; however it
does handle user-defined classes!)
A. Like the previous question, historically, there wasn't. The
library module "pickle" now solves this in a very general way (though
you still can't store things like open files, sockests or windows),
and the library module "shelve" uses pickle and (g)dbm to create
presistent mappings containing arbitrary Python objects. There are
some problems with shelve when using gdbm which will be solved in
Python 1.3.
6.3. Q. Why isn't there a switch or case statement in Python?
@ -1810,6 +1913,52 @@ programs: it's easy never to have it happen during test runs if you
only insert or delete a few items per iteration -- but your users will
surely hit upon it sooner or later.
6.13. Q. Can Python be compiled to machine code, C or some other language?
A. Not easily. Python's high level data types, dynamic typing of
objects and run-time invocation of the interpreter (using eval() or
exec) together mean that a "compiled" Python program would probably
consist mostly of calls into the Python run-time system, even for
seemingly simple operations like "x+1". Thus, the performance gain
would probably be minimal.
Internally, Python source code is always translated into a "virtual
machine code" or "byte code" representation before it is interpreted
(by the "Python virtual machine" or "bytecode interpreter"). In order
to avoid the overhead of parsing and translating modules that rarely
change over and over again, this byte code is written on a file whose
name ends in ".pyc" whenever a module is parsed (from a file whose
name ends in ".py"). When the corresponding .py file is changed, it
is parsed and translated again and the .pyc file is rewritten. There
is no performance difference once the .pyc file has been loaded (the
bytecode read from the .pyc file is exactly the same as the bytecode
created by direct translation). The only difference is that loading
code from a .pyc file is faster than parsing and translating a .py
file, so the presence of precompiled .pyc files will generally improve
start-up time of Python scripts. If desired, the Lib/compileall.py
module/script can be used to force creation of valid .pyc files for a
given set of modules.
If you are looking for a way to translate Python programs in order to
distribute them in binary form, without the need to distribute the
interpreter and library as well, have a look at the freeze.py script
in the Tools/freeze directory. This creates a single binary file
incorporating your program, the Python interpreter, and those parts of
the Python library that are needed by your program. Of course, the
resulting binary will only run on the same type of platform as that
used to create it.
Hints for proper usage of freeze.py:
- the script must be in a file whose name ends in .py
- you must have installed Python fully:
make install
make libinstall
make inclinstall
make libainstall
7. Using Python on non-UNIX platforms
=====================================
@ -1872,11 +2021,12 @@ else is working on a more complete port, for details watch the list.
7.8. Q. What about IBM mainframes, or other non-UNIX platforms?
A. I haven't heard about these, except I remember once hearing about
an attempt at an OS/9 port. If you're interested in any of this, go
directly to the newsgroup and ask there, you may find exactly what you
need. For example, a port to MPE/iX 5.0 on HP3000 computers was just
announced, see <URL:http://www.allegro.com/software/>.
A. I haven't heard about these, except I remember hearing about an
OS/9 port and a port to Vxworks (both operating systems for embedded
systems). If you're interested in any of this, go directly to the
newsgroup and ask there, you may find exactly what you need. For
example, a port to MPE/iX 5.0 on HP3000 computers was just announced,
see <URL:http://www.allegro.com/software/>.
7.9. Q. Where are the source or Makefiles for the non-UNIX versions?