Python-announce-list April 2002

python-announce-list@python.org

54 participants
80 discussions

by Guido van Rossum

Here's one final posting of PEP 285. I've read (or at least skimmed) all feedback that was on our news server by 9:30am EST on April 2nd, plus anything mailed directly to me or to python-dev until now. There was a lot of negative feedback, but there was also a lot of support for the PEP. The feedback made it easy to decide on most of the smaller issues in the review section of the PEP as previously posted: even reviewers who were against the PEP mostly supported my preferences for the various details. Despite the negative feedback, I've decided to accept the PEP. The most important perceived problem is that newbies tend to write if x == True: ... where they should write if x: ... I believe this problem should be solved by education (the Zen master hits the student on the head with a stick, and the student gets enlightenment) rather than by holding back what I believe will be a useful feature. You can expect the bool type in Python 2.3; it will be in CVS tonight. --Guido van Rossum (home page: http://www.python.org/~guido/) PEP: 285 Title: Adding a bool type Version: $Revision: 1.20 $ Last-Modified: $Date: 2002/04/03 22:11:05 $ Author: guido(a)python.org (Guido van Rossum) Status: Accepted Type: Standards Track Created: 8-Mar-2002 Python-Version: 2.3 Post-History: 8-Mar-2002, 30-Mar-2002, 3-Apr-2002 Abstract This PEP proposes the introduction of a new built-in type, bool, with two constants, False and True. The bool type would be a straightforward subtype (in C) of the int type, and the values False and True would behave like 0 and 1 in most respects (for example, False==0 and True==1 would be true) except repr() and str(). All built-in operations that conceptually return a Boolean result will be changed to return False or True instead of 0 or 1; for example, comparisons, the "not" operator, and predicates like isinstance(). Review I've collected enough feedback to last me a lifetime, so I declare the review period officially OVER. I had Chinese food today; my fortune cookie said "Strong and bitter words indicate a weak cause." It reminded me of some of the posts against this PEP... :-) Anyway, here are my BDFL pronouncements. (Executive summary: I'm not changing a thing; all variants are rejected.) 1) Should this PEP be accepted? => Yes. There have been many arguments against the PEP. Many of them were based on misunderstandings. I've tried to clarify some of the most common misunderstandings below in the main text of the PEP. The only issue that weighs at all for me is the tendency of newbies to write "if x == True" where "if x" would suffice. More about that below too. I think this is not a sufficient reason to reject the PEP. 2) Should str(True) return "True" or "1"? "1" might reduce backwards compatibility problems, but looks strange. (repr(True) would always return "True".) => "True". Almost all reviewers agree with this. 3) Should the constants be called 'True' and 'False' (similar to None) or 'true' and 'false' (as in C++, Java and C99)? => True and False. Most reviewers agree that consistency within Python is more important than consistency with other languages. 4) Should we strive to eliminate non-Boolean operations on bools in the future, through suitable warnings, so that for example True+1 would eventually (in Python 3000) be illegal? => No. There's a small but vocal minority that would prefer to see "textbook" bools that don't support arithmetic operations at all, but most reviewers agree with me that bools should always allow arithmetic operations. 5) Should operator.truth(x) return an int or a bool? => bool. Tim Peters believes it should return an int, but almost all other reviewers agree that it should return a bool. My rationale: operator.truth() exists to force a Boolean context on its argument (it calls the C API PyObject_IsTrue()). Whether the outcome is reported as int or bool is secondary; if bool exists there's no reason not to use it. (Under the PEP, operator.truth() now becomes an alias for bool(); that's fine.) 6) Should bool inherit from int? => Yes. In an ideal world, bool might be better implemented as a separate integer type that knows how to perform mixed-mode arithmetic. However, inheriting bool from int eases the implementation enormously (in part since all C code that calls PyInt_Check() will continue to work -- this returns true for subclasses of int). Also, I believe this is right in terms of substitutability: code that requires an int can be fed a bool and it will behave the same as 0 or 1. Code that requires a bool may not work when it is given an int; for example, 3 & 4 is 0, but both 3 and 4 are true when considered as truth values. 7) Should the name 'bool' be changed? => No. Some reviewers have argued for boolean instead of bool, because this would be easier to understand (novices may have heard of Boolean algebra but may not make the connection with bool) or because they hate abbreviations. My take: Python uses abbreviations judiciously (like 'def', 'int', 'dict') and I don't think these are a burden to understanding. To a newbie, it doesn't matter whether it's called a waffle or a bool; it's a new word, and they learn quickly what it means. One reviewer has argued to make the name 'truth'. I find this an unattractive name, and would actually prefer to reserve this term (in documentation) for the more abstract concept of truth values that already exists in Python. For example: "when a container is interpreted as a truth value, an empty container is considered false and a non-empty one is considered true." 8) Should we strive to require that Boolean operations (like "if", "and", "not") have a bool as an argument in the future, so that for example "if []:" would become illegal and would have to be writen as "if bool([]):" ??? => No!!! Some people believe that this is how a language with a textbook Boolean type should behave. Because it was brought up, others have worried that I might agree with this position. Let me make my position on this quite clear. This is not part of the PEP's motivation and I don't intend to make this change. (See also the section "Clarification" below.) Rationale Most languages eventually grow a Boolean type; even C99 (the new and improved C standard, not yet widely adopted) has one. Many programmers apparently feel the need for a Boolean type; most Python documentation contains a bit of an apology for the absence of a Boolean type. I've seen lots of modules that defined constants "False=0" and "True=1" (or similar) at the top and used those. The problem with this is that everybody does it differently. For example, should you use "FALSE", "false", "False", "F" or even "f"? And should false be the value zero or None, or perhaps a truth value of a different type that will print as "true" or "false"? Adding a standard bool type to the language resolves those issues. Some external libraries (like databases and RPC packages) need to be able to distinguish between Boolean and integral values, and while it's usually possible to craft a solution, it would be easier if the language offered a standard Boolean type. This also applies to Jython: some Java classes have separately overloaded methods or constructors for int and boolean arguments. The bool type can be used to select the boolean variant. (The same is apparently the case for some COM interfaces.) The standard bool type can also serve as a way to force a value to be interpreted as a Boolean, which can be used to normalize Boolean values. When a Boolean value needs to be normalized to one of two values, bool(x) is much clearer than "not not x" and much more concise than if x: return 1 else: return 0 Here are some arguments derived from teaching Python. When showing people comparison operators etc. in the interactive shell, I think this is a bit ugly: >>> a = 13 >>> b = 12 >>> a > b 1 >>> If this was: >>> a > b True >>> it would require a millisecond less thinking each time a 0 or 1 was printed. There's also the issue (which I've seen baffling even experienced Pythonistas who had been away from the language for a while) that if you see: >>> cmp(a, b) 1 >>> cmp(a, a) 0 >>> you might be tempted to believe that cmp() also returned a truth value, whereas in reality it can return three different values (-1, 0, 1). If ints were not (normally) used to represent Booleans results, this would stand out much more clearly as something completely different. Specification The following Python code specifies most of the properties of the new type: class bool(int): def __new__(cls, val=0): # This constructor always returns an existing instance if val: return True else: return False def __repr__(self): if self: return "True" else: return "False" __str__ = __repr__ def __and__(self, other): if isinstance(other, bool): return bool(int(self) & int(other)) else: return int.__and__(self, other) __rand__ = __and__ def __or__(self, other): if isinstance(other, bool): return bool(int(self) | int(other)) else: return int.__or__(self, other) __ror__ = __or__ def __xor__(self, other): if isinstance(other, bool): return bool(int(self) ^ int(other)) else: return int.__xor__(self, other) __rxor__ = __xor__ # Bootstrap truth values through sheer willpower False = int.__new__(bool, 0) True = int.__new__(bool, 1) The values False and True will be singletons, like None. Because the type has two values, perhaps these should be called "doubletons"? The real implementation will not allow other instances of bool to be created. True and False will properly round-trip through pickling and marshalling; for example pickle.loads(pickle.dumps(True)) will return True, and so will marshal.loads(marshal.dumps(True)). All built-in operations that are defined to return a Boolean result will be changed to return False or True instead of 0 or 1. In particular, this affects comparisons (<, <=, ==, !=, >, >=, is, is not, in, not in), the unary operator 'not', the built-in functions callable(), hasattr(), isinstance() and issubclass(), the dict method has_key(), the string and unicode methods endswith(), isalnum(), isalpha(), isdigit(), islower(), isspace(), istitle(), isupper(), and startswith(), the unicode methods isdecimal() and isnumeric(), and the 'closed' attribute of file objects. The predicates in the operator module are also changed to return a bool, including operator.truth(). Because bool inherits from int, True+1 is valid and equals 2, and so on. This is important for backwards compatibility: because comparisons and so on currently return integer values, there's no way of telling what uses existing applications make of these values. It is expected that over time, the standard library will be updated to use False and True when appropriate (but not to require a bool argument type where previous an int was allowed). This change should not pose additional problems and is not specified in detail by this PEP. C API The header file "boolobject.h" defines the C API for the bool type. It is included by "Python.h" so there is no need to include it directly. The existing names Py_False and Py_True reference the unique bool objects False and True (previously these referenced static int objects with values 0 and 1, which were not unique amongst int values). A new API, PyObject *PyBool_FromLong(long), takes a C long int argument and returns a new reference to either Py_False (when the argument is zero) or Py_True (when it is nonzero). To check whether an object is a bool, the macro PyBool_Check() can be used. The type of bool instances is PyBoolObject *. The bool type object is available as PyBool_Type. Clarification This PEP does *not* change the fact that almost all object types can be used as truth values. For example, when used in an if statement, an empty list is false and a non-empty one is true; this does not change and there is no plan to ever change this. The only thing that changes is the preferred values to represent truth values when returned or assigned explicitly. Previously, these preferred truth values were 0 and 1; the PEP changes the preferred values to False and True, and changes built-in operations to return these preferred values. Compatibility Because of backwards compatibility, the bool type lacks many properties that some would like to see. For example, arithmetic operations with one or two bool arguments is allowed, treating False as 0 and True as 1. Also, a bool may be used as a sequence index. I don't see this as a problem, and I don't want evolve the language in this direction either. I don't believe that a stricter interpretation of "Booleanness" makes the language any clearer. Another consequence of the compatibility requirement is that the expression "True and 6" has the value 6, and similarly the expression "False or None" has the value None. The "and" and "or" operators are usefully defined to return the first argument that determines the outcome, and this won't change; in particular, they don't force the outcome to be a bool. Of course, if both arguments are bools, the outcome is always a bool. It can also easily be coerced into being a bool by writing for example "bool(x and y)". Resolved Issues (See also the Review section above.) - Because the repr() or str() of a bool value is different from an int value, some code (for example doctest-based unit tests, and possibly database code that relies on things like "%s" % truth) may fail. It is easy to work around this (without explicitly referencing the bool type), and it is expected that this only affects a very small amount of code that can easily be fixed. - Other languages (C99, C++, Java) name the constants "false" and "true", in all lowercase. For Python, I prefer to stick with the example set by the existing built-in constants, which all use CapitalizedWords: None, Ellipsis, NotImplemented (as well as all built-in exceptions). Python's built-in namespace uses all lowercase for functions and types only. - It has been suggested that, in order to satisfy user expectations, for every x that is considered true in a Boolean context, the expression x == True should be true, and likewise if x is considered false, x == False should be true. In particular newbies who have only just learned about Boolean variables are likely to write if x == True: ... instead of the correct form, if x: ... There seem to be strong psychological and linguistic reasons why many people are at first uncomfortable with the latter form, but I believe that the solution should be in education rather than in crippling the language. After all, == is general seen as a transitive operator, meaning that from a==b and b==c we can deduce a==c. But if any comparison to True were to report equality when the other operand was a true value of any type, atrocities like 6==True==7 would hold true, from which one could infer the falsehood 6==7. That's unacceptable. (In addition, it would break backwards compatibility. But even if it didn't, I'd still be against this, for the stated reasons.) Newbies should also be reminded that there's never a reason to write if bool(x): ... since the bool is implicit in the "if". Explicit is *not* better than implicit here, since the added verbiage impairs redability and there's no other interpretation possible. There is, however, sometimes a reason to write b = bool(x) This is useful when it is unattractive to keep a reference to an arbitrary object x, or when normalization is required for some other reason. It is also sometimes appropriate to write i = int(bool(x)) which converts the bool to an int with the value 0 or 1. This conveys the intention to henceforth use the value as an int. Implementation A complete implementation in C has been uploaded to the SourceForge patch manager: http://python.org/sf/528022 This will soon be checked into CVS for python 2.3a0. Copyright This document has been placed in the public domain. Local Variables: mode: indented-text indent-tabs-mode: nil fill-column: 70 End:

18 years, 3 months

ActiveState Programming Survey - Win $1000 O'Reilly Bookshelf

by Shantel Shave

ActiveState is excited to offer you the chance to share your opinion, and win a $1000 O'Reilly Bookshelf! As open source programmers and users ourselves, we really believe in the power of collaboration. Your feedback is invaluable in helping us to better serve the Python community through our open source projects and product development. Please share your thoughts by completing our online Programming Survey. All respondents have the option of entering a draw to win a $1000 O'Reilly Bookshelf. If you win, you'll be able to customize your prize from all available titles in the O'Reilly catalog, to a total value of $1000! Survey must be completed by April 8, 2002. Draw to be held April 10, 2002. To take the survey, please click here: http://www.ActiveState.com/AS_Programming_Survey Thank you! ActiveState

18 years, 3 months

Python and Zope Banner Exchange News

by Christopher Lozinski

The python and zope Banner exchange has been in operation now for a while at: http://www.pythonandzope.com/BannerInfo Thanks to user feedback, I have now expanded the scope to include open source. So it is now called the "Open Source Banner Exchange." You are invited to submit your banners. I believe that by bringing together disparate open source web sites, this service will provide a much needed marketing boost to the python and zope community. I invite you to join, just email me your banner. Regards Christopher Lozinski 510 795 6086

18 years, 3 months

Romance object sharing

by Lamy Jean-Baptiste

Hi everyone ! I want to introduce Romance. Romance is an heterogeneous vision of programming / hacking. It relies on a light dynamic object sharing protocol for sharing between different programmic languages and programs (such as desktop applications). In the future Romance will be more than that. It may provide a full library, including even a graphic toolkit ! Romance is a free (GPL'ed) alternative to .NET, CORBA / Bonobo or XML-RPC. It allows to share objects between languages, but keeps the each language's interpreter (contrary to .NET) and look-and-feel (you code Python, not C#). Romance currently support Python, Guile (Scheme) and C. Future versions will support other scripts languages (Perl, Ruby, ...), Lisp / Scheme (ELisp, ...) and other dynamic languages (Smalltalk, OCaml)... Romance is available at : http://oomadness.tuxfamily.org/romance/en/index.html http://savannah.gnu.org/projects/romance The use of Romance in Python is totally transparent. Here is an example of a Romance server : # Step 1: import and init Romance ! import romance # Step 2: create our stuff : the Person factory class Person: def __init__(self, name, proof): self.name = name self.proof = proof def get_description(self): return "%s is a %s." % (self.name, self.proof) # Step 3: make it available to any Romance app as "romance.Person" romance.Person = Person # Step 4: wait for client ! romance.serve_forever() And the corresponding client : # Step 1: import and init Romance ! import romance # Step 2: access to Romance lib and data (and modify them if you want !!!) # Here, create me as a person ! jiba = romance.Person("Jiba", "hacker") print "My name is :", jiba.name print "More precision :", jiba.get_description() print print "Server is in %s" % jiba.__lang__() => My name is : Jiba => More precision : Jiba is a hacker. => => Server is in python The client is in Python too (because comp.lang.python !), but it can be Guile, or whatever "romantic" language ;-) Jiba

18 years, 3 months

pythonchess - Stretching the Python

by Jyrki Alakuijala

Python is an excellent language for most purposes. However, it is not the language of choice for complex, inhomogeneous computation intensive tasks. Computer chess programming is probably one of the best examples of such tasks. However, I have, together with my friend and colleague Hannu Helminen, coded a GPLed computer chess program in Python/Tkinter. http://www.kolumbus.fi/jyrki.alakuijala/pychess.html best regards, Jyrki Alakuijala

18 years, 3 months

Programming with Python and Qt.

by Boudewijn Rempt

Well, I'd like to finally officially announce that my book, _GUI Programming with Python using the Qt Toolkit_ is now officially available on paper. Whew! You buy it directly from the publisher's website: http://www.opendocs.org, or, preferably, at your favourite local or on-line bookshop. For instance, Amazon lists it as: http://www.amazon.com/exec/obidos/ASIN/0970033044/qid=1017685892/sr=8-1/ref… (And I wonder how that's going to come across.) The ISBN is 0-97003300-4-4. Anyway, I've written about 160.000 words of English prose and code, all about Qt, PyQt, sip, Qt Designer and BlackAdder. I cover both Qt 2 and Qt 3 in a lot of detail. All source code to the examples is included on a cd-rom, and Opendocs will shortly open a webforum where I'll post updated code and where people can discuss problems. You can read the book online at: http://www.opendocspublishing.com/pyqt. -- Boudewijn Rempt | http://www.valdyas.org

18 years, 3 months

PMS 0.2.18 -- The April Fool Serious Release

by Moshe Zadka

I am pleased to announce PMS, Python Mail System, is released in version 0.2.18 PMS is an MUA library written in Python, supporting multiple backends and front ends. It is availbale from http://pythonms.sf.net * Bug fixes, imported from the Debian fixes * Accessing MH folders over ssh supported now. This release is completely serious. There is nothing funny about it. -- Moshe Zadka

18 years, 3 months

ANN: Twisted 0.16.0

by Itamar Shtull-Trauring

Twisted is an event-based framework for internet applications. For more information, visit: http://www.twistedmatrix.com or join the list at: http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python Twisted joins the fight against Software Piracy =============================================== The main focus of this release is our new licensing scheme. The Business Software Alliance may have put it best, in their page on anti-piracy (http://www.bsa.org/usa/antipiracy/): "Software pirates not only steal from the companies that make the software, but with less money for research and development of new software, all users are hurt. That's why all software piracy - even one copy you make for a friend, is illegal." Software piracy is a serious crime, and one that the Open Source community has been remarkably lax in pursuing and protecting against. This is why Twisted Matrix Laboratories is taking the forefront in Open Source software registration technology. In order to do your part to prevent the tragedy of unregistered, unlicensed software, all you need to do is go to http://www.twistedmatrix.com/license and enter your user information to obtain a license key. You can provide us with as much or as little information as you like! For more information on how Twisted helps you run licensed, unpirated Open-Source software, visit: http://twistedmatrix.com/documents/howto/register What's New in 0.16.0 ==================== - Added Qt event loop support - FTP client protocol support - Reworked coil - a web-based configuration system for Twisted servers - Win32 event loop can now run subprocesses - Automatic log rotation for servers (and USR1 signal for manual rotation) - Improved support for registering shutdown methods - Better XML-RPC integration - Bug fixes, small feature improvements, and more. What is Twisted? ================ Twisted is an event-based framework for internet applications. It includes a web server, a telnet server, a multiplayer RPG engine, a generic client and server for remote object access, and APIs for creating new protocols and services. Twisted supports integration of the Tk, GTK+, Qt or wxPython event loop with its main event loop. The Win32 event loop is also supported, as is basic support for running servers on top of Jython. Twisted currently supports the following protocols, all implemented in pure python, most of them as both servers and clients: - FTP - HTTP - SOCKSv4 - SMTP - IRC - telnet - POP3 - AOL's instant messaging TOC - OSCAR, used by AOL-IM as well as ICQ (client only) - DNS - LDAP (client only) - finger - Echo, discard, chargen and friends - Twisted Perspective Broker For more information, visit http://www.twistedmatrix.com, or join the list at http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python

18 years, 3 months

The fastest XML parser around

by Andy Robinson

ReportLab (www.reportlab.com) are proud to announce the release of pyRXP, the fastest XML parsing toolkit for python, and possibly for any other language anywhere: http://www.reportlab.com/xml/pyrxp.html pyRXP is a wrapper around the excellent RXP parser developed by Richard Tobin at the University of Edinburgh. Our goal is very simple: get an entire XML document into memory, and validated, as quickly and efficiently as possible. You can parse and validate Hamlet in a tenth of a second on a standard PC. pyRXP constructs a tree of tuples in memory with a single API call; the tree is easy to navigate in standard Python code and can be wrapped up with DOM-like 'lazy accessor' nodules. It is standards-compliant and validating, and is at least 30x faster and 6x more memory efficient than the (non-validating) minidom parser in the standard Python distribution. It also comfortably beats the Microsoft and Java (Xerces) parsers in our tests. Enjoy! Andy Robinson CEO/Chief Architect, ReportLab Inc. April 1st 2001

18 years, 3 months

Webware for Python 0.7

by Geoffrey Talvola

Webware for Python 0.7 is now available! Webware for Python is a suite of software components for developing object-oriented, web-based applications. The suite uses well known design patterns and includes popular features such as: * A fast, easy-to-use application server * Servlets * Python Server Pages (PSP) * Object-relational mapper * Task scheduler * User manager with authentication * CGI wrapper Key goals of the project include: * Python-oriented. * Object-oriented. * An expansive suite of components and features to cover common needs of web developers. * Modular architecture where components can be used together or independently. * Excellent documentation and numerous examples. * Open source development and community (Python-style license). For more information or to download Webware 0.7 see http://webware.sourceforge.net ------------------------------------------------ Changes since version 0.6.1: Python 2.0 or higher is now required. Components of Webware no longer have independent version numbers. There is just an overall Webware version number. Each component still has an independent status of alpha, beta, etc. New option "gobblewhitespace" in Python Server Pages lets you write if/else and try/except statements in a more natural manner. New option "formatter" in Python Server Pages lets you specify an alternate formatter function to use instead of str(). New feature in MiddleKit: model inheritance. See the user's guide for details. Improvements to the CSV functionality in MiscUtils. WebKit features: - PickleRPC as a more Pythonic alternative to XML-RPC - SessionPrefix setting that can be used with mod_rewrite for easy load balancing with session affinity - improved exception reporting hooks - EmailErrorReportAsAttachment setting can be used to send HTML error pages as attachments - minor bug fixes Major speed improvements in MiddleKit. -- - Geoff Talvola gtalvola(a)attbi.com

18 years, 3 months

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Python-announce-list April 2002