🌐 Mailman 3 March 2003 - Python-list - python.org

critical section
by John Burton March 3, 2003

March 3, 2003

Are there any python facilities for synchronising access to a resource from two seperate processes running python programs? Semaphores etc? Or do I have to drop down to calling OS facilities. I didn't see anything but sometimes it's hard to know what to look for,..

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My .02 on PEP308 + an extra question.
by Adonis March 3, 2003

March 3, 2003

How about something like: x = iif(cond, true, false) BUT, why mingle with all this when anyone can simply make it? >>> def iif(cond, ctrue, cfalse): ... if cond: return ctrue ... else: return cfalse ... >>> y = 7 >>> x = iif(y==1, True, False) >>> x False >>> y = 1 >>> x = iif(y==1, True, False) >>> x True >>> or am I getting the concept all wrong? Adonis

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Re: PEP 312 - Making lambdas implicit worries me, surely it's just the name 'lambda' that is bad...
by Stephen Horne March 3, 2003

March 3, 2003

On Mon, 3 Mar 2003 11:34:18 +0300 (MSK), Roman Suzi <rnd(a)onego.ru> wrote: > >If I understand correctly, functional-savvy (or even aware) people are >minority of Python programmers. So all features which advance the FP >paradigma will be countered by those who "do not need the feature". > >Will it lead to a FunPython fork in the future? I hope not! > >If FP in Python is indeed Guido's mistake, then lets deprecate lambda, >map, filter, etc and ban function objects as function arguments/results. >;-) > >Sincerely yours, Roman A.Suzi My argument in starting this thread was not to ban functional facilities - I *like* functional facilities. I simply recognise that one significant argument against 'lambda' is that it is a bad name which in itself raises some peoples hackles - one of the points raised in the PEP. I think that a differently spelled keyword would handle this problem better than an implicit lambda because I feel that hiding the lambda is going to open a whole new can of worms - programs that use lambdas will quite simply be unreadable to those who are unfamiliar with lambdas because there won't even be a 'hint' of what to look up in the manual - just an obscure use of an already common piece of punctuation. Believing that functional facilities are a good thing to have is quite different to demanding that every Python programmer must be familiar with them or else. -- steve at ninereeds dot fsnet dot co dot uk

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Re: using builtin exceptions
by Alex Martelli March 3, 2003

March 3, 2003

Erik Price wrote: > Is it considered bad practice to appropriate the "builtin" exceptions > that ship with the stdlib in our own programs? For instance, > "ValueError" is explicitly described by the documentation as being for > the use of builtin functions only ("Raised when a built-in operation or > function receives an argument that has the right type but an > inappropriate value, and the situation is not described by a more > precise exception such as IndexError."), but it's the exact same I think you may be reading the docs in a different and stricter way from how they were meant. There is no "only" in the text you quote from the docs -- that's in your interpretation. And I do not think "Y happens when X" should be interpreted as "Y happens ONLY when X, and you're forbidden from ever making Y happen in any other case [even though the current interpreter does not yet enforce this prohibition]". Explicit is better than implicit: if the docs meant such a thing, they should express it explicitly. > purpose I have in mind if I use it in my code: > > ### > def __init__(self, shift_type, shift_start, shift_stop): > if not Shift.pay_rates.has_key(shift_type): > raise KeyError > if shift_start > shift_stop: > raise ValueError > ... > ### > > So is this okay to do? I ask this not strictly from a pragmatic > perspective but also from a stylistic one.... I think it's OK regarding the issue in Subject:. It's probably suitable for enhancements on other scores -- e.g. if this is the __init__ for class Shift, or a subclass thereof which does not override the class attribute named pay_rates, then I think the reference should be to self.pay_rates, NOT to Shift.pay_rates, to allow future subclasses to perform "data overriding" on that attribute (as discussed in a recent thread about Borg vs Singleton). But I don't think this is what you're asking about... Alex

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Re: How to get IP address
by sandorlevi＠yahoo.com March 3, 2003

March 3, 2003

If you want to determine your external IP, AFAIK, you must ask a machine that's external to your network. The simplest way is to visit http://www.showmyip.com/ ---- levi Nagy László Zsolt <nagylzs(a)freemail.hu> wrote in message news:<mailman.1046613969.13927.python-list(a)python.org>... > > > > > >Nagy L=E1szl=F3 Zsolt <nagylzs(a)freemail.hu> wrote in message news:<mailm= > an.1046487302.8558.python-list(a)python.org>... > > =20 > > > >>I'm trying to get all inet addresses of a machine in python. Is there a= > =20 > >>way to do it using > >>the standard library? I found a solution on Google and in Python=20 > >>CookBook but they > >>are platform dependent. I need a platform-independent solution. Thank=20 > >>you in advance. > >> > >> Laci 1.0 > >> =20 > >> > > > >How about this? I only have one IP on my box so I do not know if this > >will work for you.. > > > >socket.gethostbyaddr(socket.gethostname()) > > > >You could probably use the loopback as the parameter, like: > > > >socket.gethostbyaddr('localhost') > > > >Both of these will return a tuple in the form of (hostname, aliaslist, > >ipaddrlist). This is in 7.2 of the Python docs if you need to check > >other variations. > > > Sorry, but this does not help me. I want to determine the IP address=20 > because I want to send my external > IP address to a dynamic DNS provider (in an A record). I get my IP=20 > address with DHCP and I'm > writting a program that assigns a DNS name to a given IP address. So my=20 > hostname may have a bad IP address > assigned at the time when I need the IP address. IP address is a lower=20 > level than DNS name. I can have an IP > address without hostname. Can you tell me a solution in the case when I=20 > have no valid DNS name? > Thanks. > > Laci 1.0 > > > > --

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RE: Why no RE match of A AND B?
by Harvey Thomas March 3, 2003

March 3, 2003

Paddy wrote: > > Just looking through the docs to confirm it and their seems > to be no regular expression > construct that matches 'A and B' - an equivalent to the '|' > character that matches A or B > To paraphrase the documentation it could be documented as: > > "&" > A&B, where A and B can be arbitrary REs, creates a regular > expression that will match both > A and B in any order. An arbitrary number of REs can be > separated by the "&" in this way. > This can be used inside groups as well. REs separated by "&" > are tried in arbitrary order, > the beginning of the first matching branch up to the end of > the last branch that allows > the complete pattern (all branches) to match is considered > the span of the match. > > I envision it being used where a string is accepted at > present if it matches multiple REs. > The REs could be rewritten as r"<RE#1>&<RE2>&<RE3>...". > > The use of "&" could be supported by more efficient, > (simultaneous?), matching of all > branches of the "&" construct - if such algorithms exist! > > Just an idea, > > Paddy. > One of the simplifications of SGML made in the creation of XML was the dropping of the & operator in content models. I believe there were two reasons for this: 1) & was hardly ever used. 2) Implementation problems. Suppose you have a&b&c&d&e&f&g&h. There are 40320 patterns that match this, but this is more than the number of backtracking states that the Python RE engine supports. _____________________________________________________________________ This message has been checked for all known viruses by the MessageLabs Virus Scanning Service.

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Re: My CTO is learning Python....
by Grzegorz Staniak March 3, 2003

March 3, 2003

On Sat, 1 Mar 2003 03:30:55 -0700, Bjorn Pettersen wrote: > ...time to run screeming from the building <wink>. His problem, is that > "There doesn't seem to be any good books on Python". Pressed a little > more, it was refined to "either the documentation assumes you've never > programmed before, and spends volumes of text introducing loop > constructs etc." (that was the commentary on the Tutorial <sigh>), "or, > the author seems to be in love with the language purely for its advanced > and obscure features" (he'd hoped 'Thinking in Python' would be like the > C++/Java equivalent...). Pressed a little bit further, he commented: > "what I'm really looking for is a quick introduction for someone that > allready knows C++ or Java". As a Python newbie I won't even try to comment on the remainder of your letter, but as far as reading material is concerned, have you shown him "Dive into Python" (http://diveintopython.org/)? I think that's exactly what he needs, judging from my own experience. I was in the same position and expressed my needs in the same tone. [---] > -- bjorn -- Grzegorz Staniak <gstaniak(a)zagiel.com.pl>

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Re: Vote on PEP 308 (how to reject)
by tweedgeezer＠hotmail.com March 3, 2003

March 3, 2003

Lulu of the Lotus-Eaters <mertz(a)gnosis.cx> wrote in message news:<mailman.1046632144.5492.python-list(a)python.org>... > Gerrit Holl <gerrit(a)nl.linux.org> wrote previously: > |Although it's true that if one rejects all, it's strange to have > |to do this. > > Perhaps Raymond will specify otherwise, but it seems to me that if you > wish to vote to reject the introduction of any ternary operator, you > could fill out the following: > > Q reject NONE > Q reject NONE > Q reject NONE > ... > That seems to meet all the rules. Of course, I guess this leaves the > danger that a new ternary expression spelled "NONE" (for every C, x, y) > will be added to Python :-). The *real* danger, though, is that a ternary operator will end up being added and your voice (as far as your preference for which ternary operator add if one must be added) will be unheard. Jeremy

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beginner oo programming
by Multiscan March 3, 2003

March 3, 2003

Hi all, may be it is not the right place to post this question but I an approaching oo programming using python and therefore... Suppose I want to define a new vector class. This is simple: a vector has x, y, z components. But suppose I want to be able to use/write/store the vectors in two (or more) different coordinate systems as, e.g. cartesian and oblique, and that the transformation from one system to another is variable. For example. Suppose you have a cartesian coordinate system {(1, 0), (0,1)} and an oblique one {(1, 0), (a, b)} with b != 0 The way to transform a vector from one system to the other depends on the ration a/b. Right ? Now what is the best way to add to the vectors the knowledge of the transformation relation ? I think the best is always to store the vectors with a unique corrdinate system and then to add methods to get the coordinates on the other coordinate systems. But How do I teach to the vector object what the transformation relation (the a/b ratio in the above example) is ? Should each istance of vector class contain also a reference to the coordinate system object ? Or should I include the transformation relation as a parameter for the getcoordinate method ? What is the coordinate system object disappears or change address ? Should it be a sort of global object ? If I have a list of vectors, how do I store only once the information on the reference system ? Should I consider inheritance ? Thanks in advance for any information. giovanni

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Shared Memory
by ipellew＠pipemedia.co.uk March 3, 2003

March 3, 2003

Hi; Has any one done any work with Python using Shared Memory ! I have the need to load some small Database tables into memory that I will constantly use. In C I would simply create some shared memory (The Unix world) and put my data there. Any help / pointers please. Regards Ian

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