Re: hanning python
On Sep 9, 7:01 pm, sturlamolden sturlamol...@yahoo.no wrote: On 9 Sep, 16:57, pdpi pdpinhe...@gmail.com wrote: Raising this to 1 million, rather than 100, nodes in the window, the timing difference between your version and NumPy's is tiny (but numpy still edges you out, but just barely), but they trounce my naive version, being around 7 or 8 times faster the list comprehension I suggested. Premature optimization is the root of all evil in computer programming. Speed is not the issue here. Sure it is. And safety. And practicality. And all the other reasons why people use libraries rather than reinventing the wheel every time they fire up their editors. Given the OP's question, a snarky you're not competent enough to do scientific computing serves no purpose, where pointing him to NumPy (and SciPy, I forgot to mention that bit) serves him much better. -- http://mail.python.org/mailman/listinfo/python-list
Re: hanning python
On Sep 9, 3:27 am, sturlamolden sturlamol...@yahoo.no wrote: On 9 Sep, 00:24, Steven D'Aprano ste...@remove.this.cybersource.com.au wrote: A decent vendor-supplied implementation will include error checking that you otherwise would need to implement yourself, so yes. Not for code like this: import numpy as np n = np.arange(101) w = 0.5*(1.0-np.cos(2*np.pi*n/(100.))) Well, I went and dug into NumPy. They write it as 0.5 - 0.5 * cos (...), and special case N = 1, and properly error check N 1. Still, probably because of differences in dictionary look ups (because of namespace scopes), np.hanning, on average, takes a wee bit over half as long as your case, and yours is only a shade faster than window = [0.5 - math.cos(2 * x * math.pi /100.) for x in range(101)] (Yes, I know I should've used xrange instead of range) -- http://mail.python.org/mailman/listinfo/python-list
Re: hanning python
On Sep 9, 3:46 pm, pdpi pdpinhe...@gmail.com wrote: On Sep 9, 3:27 am, sturlamolden sturlamol...@yahoo.no wrote: On 9 Sep, 00:24, Steven D'Aprano ste...@remove.this.cybersource.com.au wrote: A decent vendor-supplied implementation will include error checking that you otherwise would need to implement yourself, so yes. Not for code like this: import numpy as np n = np.arange(101) w = 0.5*(1.0-np.cos(2*np.pi*n/(100.))) Well, I went and dug into NumPy. They write it as 0.5 - 0.5 * cos (...), and special case N = 1, and properly error check N 1. Still, probably because of differences in dictionary look ups (because of namespace scopes), np.hanning, on average, takes a wee bit over half as long as your case, and yours is only a shade faster than window = [0.5 - math.cos(2 * x * math.pi /100.) for x in range(101)] (Yes, I know I should've used xrange instead of range) Sorry, should've been smarter than this. Raising this to 1 million, rather than 100, nodes in the window, the timing difference between your version and NumPy's is tiny (but numpy still edges you out, but just barely), but they trounce my naive version, being around 7 or 8 times faster the list comprehension I suggested. So implementing this in vanilla python instead of using numpy would hurt performance a fair bit, and odds are the OP is going to put this to use somewhere that involves more maths, which makes learning about numpy well worth having asked the question here. -- http://mail.python.org/mailman/listinfo/python-list
Re: hanning python
On Sep 8, 12:36 pm, Pierre pierre.gaill...@gmail.com wrote: Hello, anyone knows what is the python equivalent of the matlab's hanning function. Note that in matlab hann and hanning are different. Thanks ! I assume you mean the tapering function mentioned here: http://mathworld.wolfram.com/HanningFunction.html Python is a general purpose language, unlike the maths-specialized MATLAB. I suggest you look into numpy, in which, a quick googling suggests, an implementation of a the Hanning function is provided. In fact, if you're using python to replace matlab in any meaningful way, you'll probably want to use numpy anyway. -- http://mail.python.org/mailman/listinfo/python-list
Re: hanning python
On Sep 8, 1:55 pm, sturlamolden sturlamol...@yahoo.no wrote: On 8 Sep, 13:36, Pierre pierre.gaill...@gmail.com wrote: anyone knows what is the python equivalent of the matlab's hanning function. Note that in matlab hann and hanning are different. If you don't know how to compute a von Hann window, you are not competent to do any scientific programming. Seriously! Come, come. I think it's a good rule that, where available, a vendor- supplied implementation is the preferable choice until proven otherwise. I assume you are using NumPy and SciPy, so consider scipy.signal.hanning for convinience. -- http://mail.python.org/mailman/listinfo/python-list
Re: Extracting patterns after matching a regex
On Sep 8, 1:56 pm, Martin mdeka...@gmail.com wrote: Hi, I need to extract a string after a matching a regular expression. For example I have the string... s = FTPHOST: e4ftl01u.ecs.nasa.gov and once I match FTPHOST I would like to extract e4ftl01u.ecs.nasa.gov. I am not sure as to the best approach to the problem, I had been trying to match the string using something like this: m = re.findall(rFTPHOST, s) But I couldn't then work out how to return the e4ftl01u.ecs.nasa.gov part. Perhaps I need to find the string and then split it? I had some help with a similar problem, but now I don't seem to be able to transfer that to this problem! Thanks in advance for the help, Martin What you're doing is telling python look for all matches of 'FTPHOST'. That doesn't really help you much, because you pretty much expect FTPHOST to be there anyway, so finding it means squat. What you _really_ want to tell it is Look for things shaped like 'FTPHOST: ftpaddress', and tell me what ftpaddress actually is. Look here: http://docs.python.org/howto/regex.html#grouping. That'll explain how to accomplish what you're trying to do. -- http://mail.python.org/mailman/listinfo/python-list
Re: Extracting patterns after matching a regex
On Sep 8, 3:21 pm, nn prueba...@latinmail.com wrote: On Sep 8, 9:55 am, Mart. mdeka...@gmail.com wrote: On Sep 8, 2:16 pm, Andreas Tawn andreas.t...@ubisoft.com wrote: Hi, I need to extract a string after a matching a regular expression. For example I have the string... s = FTPHOST: e4ftl01u.ecs.nasa.gov and once I match FTPHOST I would like to extract e4ftl01u.ecs.nasa.gov. I am not sure as to the best approach to the problem, I had been trying to match the string using something like this: m = re.findall(rFTPHOST, s) But I couldn't then work out how to return the e4ftl01u.ecs.nasa.gov part. Perhaps I need to find the string and then split it? I had some help with a similar problem, but now I don't seem to be able to transfer that to this problem! Thanks in advance for the help, Martin No need for regex. s = FTPHOST: e4ftl01u.ecs.nasa.gov If FTPHOST in s: return s[9:] Cheers, Drea Sorry perhaps I didn't make it clear enough, so apologies. I only presented the example s = FTPHOST: e4ftl01u.ecs.nasa.gov as I thought this easily encompassed the problem. The solution presented works fine for this i.e. re.search(r'FTPHOST: (.*)',s).group(1). But when I used this on the actual file I am trying to parse I realised it is slightly more complicated as this also pulls out other information, for example it prints e4ftl01u.ecs.nasa.gov\r\n', 'FTPDIR: /PullDir/0301872638CySfQB\r\n', 'Ftp Pull Download Links: \r\n', 'ftp://e4ftl01u.ecs.nasa.gov/PullDir/ 0301872638CySfQB\r\n', 'Down load ZIP file of packaged order:\r\n', etc. So I need to find a way to stop it before the \r slicing the string wouldn't work in this scenario as I can envisage a situation where the string lenght increases and I would prefer not to keep having to change the string. Many thanks It is not clear from your post what the input is really like. But just guessing this might work: print s 'MEDIATYPE: FtpPull\r\n', 'MEDIAFORMAT: FILEFORMAT\r\n','FTPHOST: e4ftl01u.ecs.nasa.gov\r\n', 'FTPDIR: /PullDir/0301872638CySfQB\r \n','Ftp Pull Download Links: \r\n' re.search(r'FTPHOST: (.*?)\\r',s).group(1) 'e4ftl01u.ecs.nasa.gov' Except, I'm assuming, the OP's getting the data from a (windows- formatted) file, so \r\n shouldn't be escaped in the regex: re.search(r'FTPHOST: (.*?)\r',s).group(1) -- http://mail.python.org/mailman/listinfo/python-list
Re: Convert points to polygon shapefile
On Jul 24, 11:21 am, Luis Pedro Almeida lpm...@ualg.pt wrote: Dear all, I would like to know how to convert a list of points into a polygon shapefile (esri). Thanks! Best regards, Luis Pedro Almeida I think you'd be better served by asking this question in a newsgroup dedicated to GIS software (I'm guessing that's the ESRI you meant). Still, what you want is to find the file format specification, and implement it. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python Equivalent for dd fold
On Jul 16, 3:12 pm, seldan24 selda...@gmail.com wrote: On Jul 15, 1:48 pm, Emile van Sebille em...@fenx.com wrote: On 7/15/2009 10:23 AM MRAB said... On Jul 15, 12:47 pm, Michiel Overtoom mot...@xs4all.nl wrote: seldan24 wrote: what can I use as the equivalent for the Unix 'fold' command? def fold(s,len): while s: print s[:len] s=s[len:] snip You might still need to tweak the above code as regards how line endings are handled. You might also want to tweak it if the strings are _really_ long to simply slice out the substrings as opposed to reassigning the balance to a newly created s on each iteration. Emile Thanks for all of the help. I'm almost there. I have it working now, but the 'fold' piece is very slow. When I use the 'fold' command in shell it is almost instantaneous. I was able to do the EBCDIC-ASCII conversion usng the decode method in the built-in str type. I didn't have to import the codecs module. I just decoded the data to cp037 which works fine. So now, I'm left with a large file, consisting of one extremely long line of ASCII data that needs to be sliced up into 35 character lines. I did the following, which works but takes a very long time: f = open(ascii_file, 'w') while ascii_data: f.write(ascii_data[:len]) ascii_data = ascii_data[len:] f.close() I know that Emile suggested that I can slice out the substrings rather than do the gradual trimming of the string variable as is being done by moving around the length. So, I'm going to give that a try... I'm a bit confused by what that means, am guessing that slice can break up a string based on characters; will research. Thanks for the help thus far. I'll post again when all is working fine. Assuming your rather large text file is 1 meg long, you have 1 million characters in there. 100/35 = ~29k lines. The size remaining string decreases linearly, so the average size is (100 + 0) / 2 or 500k. All said and done, you're allocating and copying a 500K string -- not once, but 29 thousand times. That's where your slowdown resides. -- http://mail.python.org/mailman/listinfo/python-list
Re: missing 'xor' Boolean operator
On Jul 15, 12:08 am, Christian Heimes li...@cheimes.de wrote: Chris Rebert wrote: Using the xor bitwise operator is also an option: bool(x) ^ bool(y) I prefer something like: bool(a) + bool(b) == 1 It works even for multiple tests (super xor): if bool(a) + bool(b) + bool(c) + bool(d) != 1: raise ValueError(Exactly one of a, b, c and d must be true) Christian if bool(a) + bool(b) + bool(c) + bool(d) != 1: is not equivalent to xor. 1 xor 1 xor 1 = 1 xor (1 xor 1) = 1 xor 0 = 1 (or = (1 xor 1) xor 1 = 0 xor 1 = 1 if you assicate to the left) -- http://mail.python.org/mailman/listinfo/python-list
Re: missing 'xor' Boolean operator
On Jul 15, 12:37 pm, Christian Heimes li...@cheimes.de wrote: pdpi wrote: On Jul 15, 12:08 am, Christian Heimes li...@cheimes.de wrote: Chris Rebert wrote: Using the xor bitwise operator is also an option: bool(x) ^ bool(y) I prefer something like: bool(a) + bool(b) == 1 It works even for multiple tests (super xor): if bool(a) + bool(b) + bool(c) + bool(d) != 1: raise ValueError(Exactly one of a, b, c and d must be true) Christian if bool(a) + bool(b) + bool(c) + bool(d) != 1: is not equivalent to xor. 1 xor 1 xor 1 = 1 xor (1 xor 1) = 1 xor 0 = 1 (or = (1 xor 1) xor 1 = 0 xor 1 = 1 if you assicate to the left) I'm well aware of the fact that I've described something differently. 'xor' can be explained as 'check if exactly one element of two elements is true'. My algorithms describes a super xor, aka 'check if exactly one element of n elements is true'. Christian Well, I just wouldn't call it a super xor then, when unicity test works much better -- especially as an alternative to an actual xor without any specification to the actual intended functionality except the exception text. -- http://mail.python.org/mailman/listinfo/python-list
Re: one-time factory in python for an experienced java guy
On Jul 14, 3:03 pm, phonky pho...@europe.com wrote: Hi I have searched all over and haven't found the solution for my problem yet. I am new to python, and all the time realize I do program python in java, which is not great. Besides being a real-life problem, I want to solve it as elegant as I can, using it to also learn about python (I know I could just hack something easy for now). That's what I want to do. I have an Account class. An Account instance has to get an account number. On instance creation, I want the account number to be generated (I don't want callers to pass the account # to ensure uniqueness): class Account(object): def __init__(self, holder): self.__accountnumber = self.__generate_account_number() Now, I do not know yet how the account number scheme looks like. For now, I just want to have an incremental number; later, when going to production, we'll need the proper one. Furthermore, as we plan to distribute the package, we want to allow custom account numbering schemes. Thus, customers should be able to plug in their own AccountNumberGenerator implementation. For now, I have a generators.py module. I have an AccountNumberGenerator base class, all subclasses should implement generate. I have an IncrementalGenerator subclass. So for now, I need to instantiate IncrementalGenerator, allowing for a future module to plugin their own generator. Any suggestions on how to do this? Thanks so much You don't want an AccountNumberGenerator class and subclassing, all you need is an iterator/generator of some form. These might help: http://docs.python.org/tutorial/classes.html#iterators http://docs.python.org/tutorial/classes.html#generators (in fact, that whole page is pretty relevant) Once your code expects one of those, it's trivially easy to plug something else in there. -- http://mail.python.org/mailman/listinfo/python-list
Re: Infinite loops and synchronization
On Jul 13, 6:06 am, Vincent Gulinao vincent.guli...@gmail.com wrote: lst = list() (lst populated by async twisted deferred callbacks) while True: if len(lst) == SOME_NUMBER: return lst Q1: is this a common OK practice? I'm worried infinite loops hogs memory. Q2: operating on list from threads (mostly appends) must be safe, right (synchronization)? Q1: I'll answer your question with another. What's so fundamentally different between your infinite loop and this one: while len(lst) != SOME_NUMBER: pass return lst which is not an infinite loop[1]. Why would yours be any worse in terms of memory than mine? Are you allocating anything that would hog memory? Of course, like Piet said, it *will* hog your CPU, so you want a time.sleep(.1) in there, at the least. Of course, the question is: why aren't you using a semaphore to let you know you can proceed, and make the provider increment the semaphore? [1] -- well, it can be, if len(lst) == SOME_NUMBER never comes about, and I'd hazard a guess that that's pretty much where your fear of memory hogging comes from: it's easy to allocate stuff and not deallocate it within a cycle, only to find the bounds on that cycle going awry. -- http://mail.python.org/mailman/listinfo/python-list
Re: Implementing a cache
On Jul 12, 2:01 pm, s...@pobox.com wrote: Nikolaus I want to implement a caching data structure in Python that Nikolaus allows me to: Nikolaus 1. Quickly look up objects using a key Nikolaus 2. Keep track of the order in which the objects are accessed Nikolaus (most recently and least recently accessed one, not a Nikolaus complete history) Nikolaus 3. Quickly retrieve and remove the least recently accessed Nikolaus object. My Cache module does #1 and #3. I'm not sure if you want #2 for internal cache maintenance or for as part of the API. http://www.smontanaro.net/python/Cache.py Skip I'm not sure whether #2 is doable at all, as written. You _need_ a complete history (at least the full ordering of the items in the cache) to be able to tell what the least recently used item is. -- http://mail.python.org/mailman/listinfo/python-list
Re: tough-to-explain Python
On Jul 10, 2:11 pm, Steven D'Aprano st...@remove-this- cybersource.com.au wrote: On Fri, 10 Jul 2009 12:54:21 +0200, Hendrik van Rooyen wrote: Steven D'Aprano st...@remove-this-cye.com.au wrote: On Wed, 08 Jul 2009 22:05:57 -0700, Simon Forman wrote: persistent idea out there that programming is a very accessible skill, like cooking or gardening, anyone can do it, and even profit from it, monetarily or otherwise, etc., and to some extent I am Programming is not like any other human activity. In practice? In principle? Programming in principle is not the same as it is performed in practice. But in either case, programming requires both the logical reasoning of mathematics and the creativity of the arts. Funnily enough, I do not buy this arty creativity stuff. - or are you talking about making a website look pretty? I must admit, it never crossed my mind that anyone here would claim that there was no creativity involved in programming, that it was all a mindless, algorithmic process capable of being done by a simple mechanical device. This is certainly the accusation made against *bad* programmers -- that they can't actually solve new, unique problems, but just apply recipes they learned without any insight or intelligence. The sort of people who program so poorly that a trained monkey could do what they do. I wholeheartedly agree. Coming up with Duff's device is nothing if not creative. My mind still reels at trying to grok it. http://www.lysator.liu.se/c/duffs-device.html Even *soup stock* fits the same profile as what Hendrik claims is almost unique to programming. On its own, soup stock is totally useless. But you make it, now, so you can you feed it into something else later on. Or instant coffee. I've always found cooking an apt metaphor for programming. You've got your well-limited for loops (cook for x minutes), your less straightforward while/until loops (roast until golden), you have your subprocedures (prepare sauce in advance/in parallel), you have some conditionals (tenderize the steak if the meat isn't really that tender), etc etc. The complexities of assignment can be easily visualized in terms of containers and mixing stuff together. Nothing makes a += b more obvious than having a bowl of cream (a), an egg (b), and adding the egg to the bowl of cream (a += b). Well, except for the part where that in that case evaluating b is destructive ;) They can't reason? Then what are they doing when they manipulate symbols? Computers aren't intelligent. They only think they are. Or, more to the point: the typical definition of reasoning tends to involve more of what defines humans as self-aware, animate beings than what is usually ascribed to computers. -- http://mail.python.org/mailman/listinfo/python-list
Re: Clarity vs. code reuse/generality
On Jul 8, 2:24 am, Paul Rubin http://phr...@nospam.invalid wrote: pdpi pdpinhe...@gmail.com writes: while abs(func(guess) - target) epsilon: guess = (lo + hi) / 2. if sense * func(guess) sense * target: hi = guess elif sense * func(guess) sense * target: lo = guess elif lo == hi: return None return guess That is completely confusing. I get the, er, impression that sense is supposed to change during the loop, and it takes much head scratching to tell whether what you have there is right or not. Also, it calls func 3 times on each loop, which could be extremely slow. You don't know what func does, so eliminating 2/3 of the calls to it is not a micro-optimization--it could be a major time saving. Yet another version: def _binary_search(x0, x1, func, target, epsilon): y0,y1 = func(x0), func(x1) while abs(y1 - target) epsilon: if x0 == x1 or cmp(y0,target) == cmp(y1,target): return None xn = (x0 + x1) / 2. yn = func(xn) if cmp(yn,target) == cmp(y0,target): x0,y0 = xn,yn else: x1,y1 = xn,yn return x1 micro-optimization was perhaps too harsh, but it is an optimization that's not obvious for the newbie, and one best learnt from experience rather than having it spoon fed. I'll restate: you should start with the cleanest code possible and mangle it for performance. Then again, that implicitly assumes that f(x) is more readable than y, which is really a matter of taste... -- http://mail.python.org/mailman/listinfo/python-list
Re: Why re.match()?
On Jul 2, 4:49 am, kj no.em...@please.post wrote: In xns9c3bca27abc36duncanbo...@127.0.0.1 Duncan Booth duncan.bo...@invalid.invalid writes: So, for example: re.compile(c).match(abcdef, 2) _sre.SRE_Match object at 0x02C09B90 re.compile(^c).search(abcdef, 2) I find this unconvincing; with re.search alone one could simply do: re.compile(^c).search(abcdef[2:]) given large enough values of abcdef, you just allocated several megs for no good reason, when re.compile(c).match(abcdef, 2) would process abcdef in-place. -- http://mail.python.org/mailman/listinfo/python-list
Re: Clarity vs. code reuse/generality
On Jul 7, 7:26 pm, Andre Engels andreeng...@gmail.com wrote: On Tue, Jul 7, 2009 at 8:01 PM, pdpipdpinhe...@gmail.com wrote: He asserts: assert lo hi but then compares: sense = cmp(func(hi), func(lo)) sense can't ever be anything other than 1. It can - there is no necessity that func is monotonically increasing. -- André Engels, andreeng...@gmail.com Yes, I realized that as I was walking home. In other news, some of you may be interested in my seminar in advanced foot-in-mouth placement. -- http://mail.python.org/mailman/listinfo/python-list
Re: Clarity vs. code reuse/generality
On Jul 7, 7:06 pm, Paul Rubin http://phr...@nospam.invalid wrote: pdpi pdpinhe...@gmail.com writes: Personally, I think the code is an unreadable mess, but that's mostly because of all the micro optimizations, not the generality of it. Here's my unoptimized, but still equally generic, version: That version doesn't use sense inside the binary search, i.e. it relies on the function being monotonically increasing. You're right, make that: def _binary_search(lo, hi, func, target, epsilon): sense = cmp(func(hi), func(lo)) if sense == 0: return None guess = (lo + hi) / 2. while abs(func(guess) - target) epsilon: guess = (lo + hi) / 2. if sense * func(guess) target: hi = guess elif sense * func(guess) target: lo = guess elif lo == hi: return None return guess Seems I had a serious brain cramp while posting that... -- http://mail.python.org/mailman/listinfo/python-list
Re: Clarity vs. code reuse/generality
On Jul 7, 7:31 pm, pdpi pdpinhe...@gmail.com wrote: On Jul 7, 7:06 pm, Paul Rubin http://phr...@nospam.invalid wrote: pdpi pdpinhe...@gmail.com writes: Personally, I think the code is an unreadable mess, but that's mostly because of all the micro optimizations, not the generality of it. Here's my unoptimized, but still equally generic, version: That version doesn't use sense inside the binary search, i.e. it relies on the function being monotonically increasing. You're right, make that: def _binary_search(lo, hi, func, target, epsilon): sense = cmp(func(hi), func(lo)) if sense == 0: return None guess = (lo + hi) / 2. while abs(func(guess) - target) epsilon: guess = (lo + hi) / 2. if sense * func(guess) target: hi = guess elif sense * func(guess) target: lo = guess elif lo == hi: return None return guess Seems I had a serious brain cramp while posting that... Actually, scratch that. def _binary_search(lo, hi, func, target, epsilon): sense = cmp(func(hi), func(lo)) if sense == 0: return None guess = (lo + hi) / 2. while abs(func(guess) - target) epsilon: guess = (lo + hi) / 2. if sense * func(guess) sense * target: hi = guess elif sense * func(guess) sense * target: lo = guess elif lo == hi: return None return guess -- http://mail.python.org/mailman/listinfo/python-list
Re: Clarity vs. code reuse/generality
On Jul 7, 8:04 pm, Dave Angel da...@ieee.org wrote: And of course your clarified function will fail if the func is monotonically decreasing. yeah, I eventually realized that and corrected it... And the assert()/ cmp() confusion too. I blame lack of sleep. The whole sign/sense thing left a really bad taste in my mouth, though, and the swapping lo and hi suggestion of yours seems like the neatest solution presented. -- http://mail.python.org/mailman/listinfo/python-list
Re: A Bug By Any Other Name ...
On Jul 6, 1:12 pm, Hendrik van Rooyen m...@microcorp.co.za wrote: Terry Reedy t@..el.edu wrote: Gabriel Genellina wrote: In this case, a note in the documentation warning about the potential confusion would be fine. How would that help someone who does not read the doc? It obviously won't. All it will do, is that it will enable people on this group, who may read the manual, to tell people who complain, to RTFM. I agree that it would be a good idea to make it an error, or a warning - this might not do what you think it does, or an are you sure? exception. :-) - Hendrik I dunno. Specifically recognizing (and emitting code code for) a token that's not actually part of the language because people coming from other languages think it exists seems like the start of a fustercluck. -- http://mail.python.org/mailman/listinfo/python-list
Re: Measuring Fractal Dimension ?
On Jun 29, 3:17 am, greg g...@cosc.canterbury.ac.nz wrote: Paul Rubin wrote: Steven D'Aprano st...@remove-this-cybersource.com.au writes: But that depends on what you call things... if electron shells are real (and they seem to be) and discontinuous, and the shells are predicted/ specified by eigenvalues of some continuous function, is the continuous function part of nature or just a theoretical abstraction? Another thing to think about: If you put the atom in a magnetic field, the energy levels of the electrons get shifted slightly. To the extent that you can vary the magnetic field continuously, you can continuously adjust the energy levels. This of course raises the question of whether it's really possible to continuously adjust a magnetic field. But it's at least possible to do so with much finer granularity than the differences between energy levels in an atom. So if there is a fundamentally discrete model underlying everything, it must be at a much finer granularity than anything we've so far observed, and the discrete things that we have observed probably aren't direct reflections of it. -- Greg Electron shells and isolated electrons stuck in a magnetic field are different phenomena that can't be directly compared. Or, at least, such a comparison requires you to explain why it's proper. -- http://mail.python.org/mailman/listinfo/python-list
Re: Passing parameters for a C program in Linux.
On Jun 30, 11:46 am, venutaurus...@gmail.com venutaurus...@gmail.com wrote: Hi all, I have to write an automted script which will test my c program. That program when run will ask for the commands. For example: local-host# ./cli Enter 1 for add Enter 2 for sub Enter 3 for mul 1 ---Our option Enter two numbers 44 33 Our option Result is 77 As shown in the above example it lists all the options and waits for user input and once given, it does some operations and waits for some more. This has to be automated. Can someone give suggestions how to do this in Python (Linux Platform in particular). Thank you, Venu. The easiest (and ugliest) way to do this would probably be to write a file input.txt and a file output.txt with each input/output value, and then to do this on the command prompt: ./a.out input.txt | diff output.txt - this will run a.out (assuming that's your program's name), feed in input.txt as input, and pipe that into diff to compute the differences between its output and output.txt -- http://mail.python.org/mailman/listinfo/python-list
Re: 3.2*2 is 9.6 ... or maybe it isn't?
On Jun 26, 11:01 am, Steven D'Aprano st...@remove-this-
cybersource.com.au wrote:
On Thu, 25 Jun 2009 12:41:13 -0600, Michael Torrie wrote:
If you want accurate math, check out other types like what is in the
decimal module:
import decimal
a=decimal.Decimal('3.2')
print a * 3
9.6
Not so. Decimal suffers from the exact same problem, just with different
numbers:
import decimal
x = decimal.Decimal('1')/decimal.Decimal('3')
3*x == 1
False
Some numbers can't be represented exactly in base 2, and some numbers
can't be represented exactly in base 10.
--
Steven
But since 10 = 2 * 5, all numbers that can be finitely represented in
binary can be represented finitely in decimal as well, with the exact
same number of places for the fractional part (and no more digits
than the binary representation in the integer part)
--
http://mail.python.org/mailman/listinfo/python-list
Re: Measuring Fractal Dimension ?
On Jun 25, 12:23 pm, Robin Becker ro...@reportlab.com wrote: Paul Rubin wrote: so does this render all the discreteness implied by quantum theory unreliable? or is it that we just cannot see(measure) the continuity that really happens? Certainly there are people like Wolfram who seem to think we're in some kind of giant calculating engine where state transitions are discontinuous. More like that axiomatic system doesn't accurately map to reality as we currently understand it. Your posts made me think that I wasn't clear in saying e and 2 are the only natural bases for logs. The log function, as the inverse of the exponential, is a pretty fundamental function. The base e exponential has a load of very natural properties, f'(x) = f (x) being an example. As the smallest admissible integer base, log 2 is also a pretty natural notion, especially in computer science, or in general all that follow from binary true/false systems. -- http://mail.python.org/mailman/listinfo/python-list
Re: Measuring Fractal Dimension ?
On Jun 25, 10:38 am, Paul Rubin http://phr...@nospam.invalid wrote:
Robin Becker ro...@reportlab.com writes:
someone once explained to me that the set of systems that are
continuous in the calculus sense was of measure zero in the set of all
systems I think it was a fairly formal discussion, but my
understanding was of the hand waving sort.
That is very straightforward if you don't mind a handwave. Let S be
some arbitrary subset of the reals, and let f(x)=0 if x is in S, and 1
otherwise (this is a discontinuous function if S is nonempty). How
many different such f's can there be? Obviously one for every
possible subset of the reals. The cardinality of such f's is the
power set of the reals, i.e. much larger than the set of reals.
On the other hand, let g be some arbitrary continuous function on the
reals. Let H be the image of Q (the set of rationals) under g. That
is, H = {g(x) such that x is rational}. Since g is continuous, it is
completely determined by H, which is a countable set. So the
cardinality is RxN which is the same as the cardinality of R.
If true that makes calculus (and hence all of our understanding of
such natural concepts) pretty small and perhaps non-applicable.
No really, it is just set theory, which is a pretty bogus subject in
some sense. There aren't many discontinuous functions in nature.
There is a philosophy of mathematics (intuitionism) that says
classical set theory is wrong and in fact there are NO discontinuous
functions. They have their own mathematical axioms which allow
developing calculus in a way that all functions are continuous.
On the other hand R Kalman (of Bucy and Kalman filter fame) likened
study of continuous linear dynamical systems to a man searching for
a lost ring under the only light in a dark street ie we search
where we can see. Because such systems are tractable doesn't make
them natural or essential or applicable in a generic sense.
Really, I think the alternative he was thinking of may have been
something like nonlinear PDE's, a horribly messy subject from a
practical point of view, but still basically free of set-theoretic
monstrosities. The Banach-Tarski paradox has nothing to do with nature.
I'll take the Banach-Tarski construct (it's not a paradox, damn it!)
over non-linear PDEs any day of the week, thankyouverymuch. :)
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Re: Measuring Fractal Dimension ?
On Jun 24, 2:58 pm, Hendrik van Rooyen m...@microcorp.co.za wrote: Steven D'Aprano ste...@remove.this.c...com.au wrote: On Mon, 22 Jun 2009 13:43:19 -0500, David C. Ullrich wrote: In my universe the standard definition of log is different froim what log means in a calculus class Now I'm curious what the difference is. Maybe he is a lumberjack, and quite all right... - Hendrik Or perhaps he works in a sewage facility. But yeah, Log2 and LogE are the only two bases that make natural sense except in specialized contexts. Base 10 (and, therefore, Log10) is an artifact of having that 10 fingers (in fact, whatever base you use, you always refer to it as base 10). -- http://mail.python.org/mailman/listinfo/python-list
Re: Measuring Fractal Dimension ?
On Jun 24, 1:32 pm, Mark Dickinson dicki...@gmail.com wrote: On Jun 24, 10:12 am, pdpi pdpinhe...@gmail.com wrote: Regarding inf ** 0, why does IEEE745 define it as 1, when there is a perfectly fine NaN value? Other links: the IEEE 754 revision working group mailing list archives are public; there was extensive discussion about special values of pow and similar functions. Here's a relevant Google search: http://www.google.com/search?q=site:grouper.ieee.org++pow+annex+D The C99 rationale document has some explanations for the choices for special values in Annex F. Look at pages 179--182 in: http://www.open-std.org/jtc1/sc22/wg14/www/C99RationaleV5.10.pdf Note that the original IEEE 754-1985 didn't give specifications for pow and other transcendental functions; so a complete specification for pow appeared in the C99 standard before it appeared in the current IEEE standard, IEEE 754-2008. Thus C99 Annex F probably had at least some small influence on the choices made for IEEE 754-2008 (and in turn, IEEE 754-1985 heavily influenced C99 Annex F). My own take on all this, briefly: - floating-point numbers are not real numbers, so mathematics can only take you so far in deciding what the 'right' values are for special cases; pragmatics has to play a role too. - there's general consensus in the numerical and mathematical community that it's useful to define pow(0.0, 0.0) to be 1. - once you've decided to define pow(0.0, 0.0) to be 1.0, it's easy to justify taking pow(inf, 0.0) to be 1.0: the same limiting arguments can be used as justification; or one can use reflection formulae like pow(1/x, y) = 1/pow(x, y), or... - one piece of general philosophy used for C99 and IEEE 754 seems to have been that NaN results should be avoided when it's possible to give a meaningful non-nan value instead. - part of the reason that pow is particularly controversial is that it's really trying to be two different functions at once: it's trying to be both a generalization of the `analytic' power function x**y = exp(y*log(x)), for real y and positive real x, and in this context one can make a good argument that 0**0 should be undefined; but at the same time it's also used in contexts where y is naturally thought of as an integer; and in the latter context bad things happen if you don't define pow(0, 0) to be 1. I really should get back to work now. Mark Thanks for the engrossing read (and damn you for making me waste valuable work hours). After perusing both C99 and the previous presentation on IEEE754, I find myself unconvinced regarding the special cases. It just stinks of bug-proneness, and I fail to see how assuming common values for exceptional cases relieves you from testing for those special cases and getting them behaving right (in an application-specific way) just the same. -- http://mail.python.org/mailman/listinfo/python-list
Re: Measuring Fractal Dimension ?
On Jun 19, 8:13 pm, Charles Yeomans char...@declaresub.com wrote: On Jun 19, 2009, at 2:43 PM, David C. Ullrich wrote: Evidently my posts are appearing, since I see replies. I guess the question of why I don't see the posts themselves \is ot here... On Thu, 18 Jun 2009 17:01:12 -0700 (PDT), Mark Dickinson dicki...@gmail.com wrote: On Jun 18, 7:26 pm, David C. Ullrich ullr...@math.okstate.edu wrote: On Wed, 17 Jun 2009 08:18:52 -0700 (PDT), Mark Dickinson Right. Or rather, you treat it as the image of such a function, if you're being careful to distinguish the curve (a subset of R^2) from its parametrization (a continuous function R - R**2). It's the parametrization that's uniformly continuous, not the curve, Again, it doesn't really matter, but since you use the phrase if you're being careful: In fact what you say is exactly backwards - if you're being careful that subset of the plane is _not_ a curve (it's sometimes called the trace of the curve. Darn. So I've been getting it wrong all this time. Oh well, at least I'm not alone: De?nition 1. A simple closed curve J, also called a Jordan curve, is the image of a continuous one-to-one function from R/Z to R2. [...] - Tom Hales, in 'Jordan's Proof of the Jordan Curve Theorem'. We say that Gamma is a curve if it is the image in the plane or in space of an interval [a, b] of real numbers of a continuous function gamma. - Claude Tricot, 'Curves and Fractal Dimension' (Springer, 1995). Perhaps your definition of curve isn't as universal or 'official' as you seem to think it is? Perhaps not. I'm very surprised to see those definitions; I've been a mathematician for 25 years and I've never seen a curve defined a subset of the plane. I have. Hmm. You left out a bit in the first definition you cite: A simple closed curve J, also called a Jordan curve, is the image of a continuous one-to-one function from R/Z to R2. We assume that each curve comes with a fixed parametrization phi_J : R/Z -¨ J. We call t in R/Z the time parameter. By abuse of notation, we write J(t) in R2 instead of phi_j (t), using the same notation for the function phi_J and its image J. Close to sounding like he can't decide whether J is a set or a function... On the contrary, I find this definition to be written with some care. I find the usage of image slightly ambiguous (as it suggests the image set defines the curve), but that's my only qualm with it as well. Thinking pragmatically, you can't have non-simple curves unless you use multisets, and you also completely lose the notion of curve orientation and even continuity without making it a poset. At this point in time, parsimony says that you want to ditch your multiposet thingie (and God knows what else you want to tack in there to preserve other interesting curve properties) and really just want to define the curve as a freaking function and be done with it. -- http://mail.python.org/mailman/listinfo/python-list
Re: Measuring Fractal Dimension ?
On Jun 17, 1:26 pm, Jaime Fernandez del Rio jaime.f...@gmail.com wrote: P.S. The snowflake curve, on the other hand, is uniformly continuous, right? The definition of uniform continuity is that, for any epsilon 0, there is a delta 0 such that, for any x and y, if x-y delta, f(x)-f (y) epsilon. Given that Koch's curve is shaped as recursion over the transformation from ___ to _/\_, it's immediately obvious that, for a delta of at most the length of , epsilon will be at most the height of /. It follows that, inversely, for any arbitrary epsilon, you find the smallest / that's still taller than epsilon, and delta is bound by the respective . (hooray for ascii demonstrations) Curiously enough, it's the recursive/self-similar nature of the Koch curve so easy to prove as uniformly continuous. -- http://mail.python.org/mailman/listinfo/python-list
Re: fastest native python database?
On Jun 18, 8:09 am, Pierre Quentel quentel.pie...@wanadoo.fr wrote:
On 18 juin, 05:28, per perfr...@gmail.com wrote:
hi all,
i'm looking for a native python package to run a very simple data
base. i was originally using cpickle with dictionaries for my problem,
but i was making dictionaries out of very large text files (around
1000MB in size) and pickling was simply too slow.
i am not looking for fancy SQL operations, just very simple data base
operations (doesn't have to be SQL style) and my preference is for a
module that just needs python and doesn't require me to run a separate
data base like Sybase or MySQL.
does anyone have any recommendations? the only candidates i've seen
are snaklesql and buzhug... any thoughts/benchmarks on these?
any info on this would be greatly appreciated. thank you
Hi,
buzhug syntax doesn't use SQL statements, but a more Pythonic syntax :
from buzhug import Base
db = Base('foo').create(('name',str),('age',int))
db.insert('john',33)
# simple queries
print db(name='john')
# complex queries
print [ rec.name for rec in db if age 30 ]
# update
rec.update(age=34)
I made a few speed comparisons with Gadfly, KirbyBase (another pure-
Python DB, not maintained anymore) and SQLite. You can find the
results on the buzhug home page :http://buzhug.sourceforge.net
The conclusion is that buzhug is much faster than the other pure-
Python db engines, and (only) 3 times slower than SQLite
- Pierre
Which means that, at this point in time, since both gadfly and sqlite
use approximately the same API, sqlite takes the lead as a core
package (post-2.5 anyway)
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Re: question about a command like 'goto ' in Python's bytecode orit's just a compiler optimization?
On Jun 17, 9:01 am, Hendrik van Rooyen m...@microcorp.co.za wrote: Diez B. Roggisch d...@n...m.web.de wrote: Getting a depression because of a compiler is a bit strong... However, yes, bytecode is similar to assembler, and in that respect higher-level control-structures are created using (conditional) jumps. The same is true for other bytecode-languages, see here for the JVM: http://java.sun.com/docs/books/jvms/second_edition/html/Overview.doc This is right. It is my opinion that it is not possible to make a useful machine, virtual or real, which executes instructions sequentially, if the instruction set does not contain a conditional jump of some sort. I have tried doing it using conditional calls, and it fails on the equivalent of the first if ..., elif ... you try to write. - Hendrik Not a matter of opinion. One of the requisite elements of a Turing Machine is conditional jumping. -- http://mail.python.org/mailman/listinfo/python-list
Re: Measuring Fractal Dimension ?
On Jun 17, 4:18 pm, Mark Dickinson dicki...@gmail.com wrote: On Jun 17, 3:46 pm, Paul Rubin http://phr...@nospam.invalid wrote: Mark Dickinson dicki...@gmail.com writes: It looks as though you're treating (a portion of?) the Koch curve as the graph of a function f from R - R and claiming that f is uniformly continuous. But the Koch curve isn't such a graph (it fails the 'vertical line test', I think you treat it as a function f: R - R**2 with the usual distance metric on R**2. Right. Or rather, you treat it as the image of such a function, if you're being careful to distinguish the curve (a subset of R^2) from its parametrization (a continuous function R - R**2). It's the parametrization that's uniformly continuous, not the curve, and since any curve can be parametrized in many different ways any proof of uniform continuity should specify exactly which parametrization is in use. Mark I was being incredibly lazy and using loads of handwaving, seeing as I posted that (and this!) while procrastinating at work. an even lazier argument: given the _/\_ construct, you prove that its vertical growth is bound: the height of / is less than 1/3 (given a length of 1 for ___), so, even if you were to build _-_ with the middle segment at height = 1/3, the maximum vertical growth would be sum 1/3^n from 1 to infinity, so 0.5. Sideways growth has a similar upper bound. 0.5 1, so the chebyshev distance between any two points on the curve is = 1. Ergo, for any x,y, f(x) is at most at chebyshev distance 1 of (y). Induce the argument for smaller values of one. -- http://mail.python.org/mailman/listinfo/python-list
Re: Exotic Logics
On Jun 17, 5:37 pm, Lie Ryan lie.1...@gmail.com wrote: Steven D'Aprano wrote: On Tue, 16 Jun 2009 22:46:14 -0700, William Clifford wrote: I was staring at a logic table the other day, and I asked myself, what if one wanted to play with exotic logics; how might one do it? This might be useful for you, and if not useful, at least it might blow your mind like it did mine. (This is not original to me -- I didn't create it. However, I can't find the original source.) Imagine for a moment that there are no boolean values. There are no numbers. They were never invented. There are no classes. There are no objects. There are only functions. Could you define functions that act like boolean values? And could you define other functions to operate on them? def true(x, y): return x def false(x, y): return y def print_bool(b): print b(true, false) String isn't considered object? Also, b/true()/false() is a function object, isn't it? Unless function is first-class, you can't pass them around like that, since you need a function pointer (a.k.a number); but if function is first-class then there it is an object. What Steven was doing was implementing some of the more basic stuff from Lambda calculus in python. If you're implementing a different system in an existing language, you'll need to use _some_ facilities of the original language to interface with the outside world. Anyway, here's a sample interactive session I just tried: def a(stuff): ... print stuff ... def b(stuff): ... stuff(abc) ... b(a) abc functions are first-class citizens in python. -- http://mail.python.org/mailman/listinfo/python-list
Re: Need to know if a file as only ASCII charaters
On Jun 16, 2:17 pm, Dave Angel da...@ieee.org wrote: Jorge wrote: Hi there, I'm making a application that reads 3 party generated ASCII files, but some times the files are corrupted totally or partiality and I need to know if it's a ASCII file with *nix line terminators. In linux I can run the file command but the applications should run in windows. Any help will be great. Thank you in advance. So, which is the assignment: 1) determine if a file has non-ASCII characters 2) determine whether the line-endings are crlf or just lf In the former case, look at translating the file contents to Unicode, specifying ASCII as source. If it fails, you have non-ASCII In the latter case, investigate the 'u' attribute of the mode parameter in the open() function. You also need to ask yourself whether you're doing a validation of the file, or doing a best guess like the file command. From your requisites, you're already assuming something that _should_ be ASCII, so it's easiest to check for ASCIIness at the binary level: Open the file as binary Loop at the bytes exit with error upon reading a byte outside the printable range (32-126 decimal) or any of a number of lower-range exceptions (\n, \t -- not \r since you want UNIX-style linefeeds) exit with success if the loop ended cleanly This supposes you're dealing strictly with ASCII, and not a full 8 bit codepage, of course. -- http://mail.python.org/mailman/listinfo/python-list
Re: Measuring Fractal Dimension ?
On Jun 15, 5:55 am, Steven D'Aprano ste...@remove.this.cybersource.com.au wrote: On Sun, 14 Jun 2009 14:29:04 -0700, Kay Schluehr wrote: On 14 Jun., 16:00, Steven D'Aprano st...@removethis.cybersource.com.au wrote: Incorrect. Koch's snowflake, for example, has a fractal dimension of log 4/log 3 ≈ 1.26, a finite area of 8/5 times that of the initial triangle, and a perimeter given by lim n-inf (4/3)**n. Although the perimeter is infinite, it is countably infinite and computable. No, the Koch curve is continuous in R^2 and uncountable. I think we're talking about different things. The *number of points* in the Koch curve is uncountably infinite, but that's nothing surprising, the number of points in the unit interval [0, 1] is uncountably infinite. But the *length* of the Koch curve is not, it's given by the above limit, which is countably infinite (it's a rational number for all n). Lawrence is right and one can trivially cover a countable infinite set with disks of the diameter 0, namely by itself. The sum of those diameters to an arbitrary power is also 0 and this yields that the Hausdorff dimension of any countable set is 0. Nevertheless, the Hausdorff dimension (or a close approximation thereof) can be calculated from the scaling properties of even *finite* objects. To say that self-similar objects like broccoli or the inner surface of the human lungs fails to nest at all scales is pedantically correct but utterly pointless. If it's good enough for Benoît Mandelbrot, it's good enough for me. -- Steven You're mixing up the notion of countability. It only applies to set sizes. Unless you're saying that there an infinite series has a countable number of terms (a completely trivial statement), to say that the length is countably finite simply does not parse correctly (let alone being semantically correct or not). This said, I agree with you: I reckon that the Koch curve, while composed of uncountable cardinality, is completely described by the vertices, so a countable set of points. It follows that you must be able to correctly calculate the Hausdorff dimension of the curve from those control points alone, so you should also be able to estimate it from a finite sample (you can arguably infer self-similarity from a limited number of self- similar generations). -- http://mail.python.org/mailman/listinfo/python-list
Re: import sqlite3
On Jun 4, 12:45 pm, willgun will...@live.cn wrote: By the way ,what does 'best regards' means at the end of a mail? regard means roughly care. Its use as best regards closing a letter (or, in this case, email), means that you care for the person you're saying goodbye to. It's just a polite way to end a letter :) -- http://mail.python.org/mailman/listinfo/python-list
Re: Can I get a technical explanation on the following error
On May 24, 6:41 pm, grocery_stocker cdal...@gmail.com wrote: How come something like '\' causes an error? Here is what I mean. [cdal...@localhost ~]$ python Python 2.6.2 (r262:71600, May 3 2009, 17:04:44) [GCC 4.1.1 20061011 (Red Hat 4.1.1-30)] on linux2 Type help, copyright, credits or license for more information. print test \ File stdin, line 1 print test \ ^ SyntaxError: EOL while scanning string literal I mean, isn't the '\' a character just like the letter 't'? Ask yourself: 'How would I tell Python to print the character when it's used as the string delimitation character?'. Unlike us (you probably didn't even blink at the usage of ' in it's versus its usage as quote delimiters in that sentence), computers can't quite tell usage from context. So you have to come up with a way to express ourselves. Many languages use the \ character as an escape character, which modifies the meaning of the next character in a string. \n, \t, \ are all common. Other languages use other conventions -- I program ABAP professionally, and it uses ' as the string delimiter, and '' as a literal -- so a string with one single ' is expressed as . The python interpreter isn't doing any bit magic here, it's just reading a \ character followed by a character and changing its interpretation of appropriately. -- http://mail.python.org/mailman/listinfo/python-list
Re: When are immutable tuples *essential*? Why can't you just use lists *everywhere* instead?
Iou need only consider having cartesian coordinate sets as the keys for an example. A 2 dimensional list might be overly expensive if your coordinates span a large area but are relatively sparse. -- http://mail.python.org/mailman/listinfo/python-list
