Re: Prime number generator
On Wednesday, July 10, 2013 4:00:59 PM UTC+2, Chris Angelico wrote:
[...]
> So, a few questions. Firstly, is there a stdlib way to find the key
> with the lowest corresponding value? In the above map, it would return
> 3, because 18 is the lowest value in the list. I want to do this with
> a single pass over the dictionary.
In [1]: prime = {2: 20, 3: 18, 5: 20, 7: 21, 11: 22, 13: 26}
In [2]: smallest_key = min(prime.iteritems(), key=lambda k_v: k_v[1])[0]
In [3]: smallest_key
Out[3]: 3
Still trying to figure out your algorithm ...
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Re: Prime number generator
On Wednesday, July 10, 2013 5:12:19 PM UTC+2, Chris Angelico wrote: > Well, that does answer the question. Unfortunately the use of lambda > there has a severe performance cost [ ...] If you care about speed, you might want to check the heapq module. Removing the smallest item and inserting a new item in a heap both cost O(log(N)) time, while finding the minimum in a dictionary requires iterating over the whole dictionary, which cost O(N) time. (untested) #before loop from heapq import * primes = [(2,2)] #heap of tuples (multiple, prime). start with 1 item, so no need for heapify #during loop smallest, prm = heappop(primes) heappush(primes, (smallest+prm, prm)) #when new prime found heappush(primes, (i+i, i)) > > Still trying to figure out your algorithm ... > It's pretty simple. [...] I understand what you are trying, but it is not immediately clear to me that it works correctly if for example a smallest factor appears twice in the list. I don't have time for it now, but it for sure can be simplified. The while loop, for example, can be replaced by an if, since it will never execute more than once (since if i is prime > 2, i+1 will be divisible by 2) -- http://mail.python.org/mailman/listinfo/python-list
Brute force sudoku cracker
Hi group, I came across some of these online sudoku games and thought after playing a game or two that I'd better waste my time writing a solver than play the game itself any longer. I managed to write a pretty dumb brute force solver that can at least solve the easy cases pretty fast. It basically works by listing all 9 possible numbers for all 81 fields and keeps on striking out possibilities until it is done. -any ideas how to easily incorporate advanced solving strategies? solve(problem1) and solve(problem2) give solutions, but solve(problem3) gets stuck... -any improvements possible for the current code? I didn't play a lot with python yet, so I probably missed some typical python tricks, like converting for-loops to list expressions. TIA, Bas *** from itertools import ifilterfalse problem1 = [' 63 7 ', ' 69 8', '97 2', ' 2 1 8 ', ' 5 8 6 9 ', ' 9 7 2 ', '6 13', '7 45 ', ' 9 14 '] problem2 = [' 3 9 7', ' 1 8', ' 1 9 ', ' 49 5 6', ' 2 1 ', '5 6 74 ', ' 5 1 ', '4 2 ', '7 5 3 '] problem3 = [' 3 5 81 ', ' 76 9 ', '4', ' 439 5 6', ' 1 7 ', '6 8 193 ', '9', ' 9 86 ', ' 61 2 8 '] #define horizontal lines, vertical lines and 3x3 blocks groups = [range(9*i,9*i+9) for i in range(9)] + \ [range(i,81,9) for i in range(9)] + \ [range(0+27*i+3*j,3+27*i+3*j) + range(9+27*i+3*j,12+27*i+3*j) + \ range(18+27*i+3*j,21+27*i+3*j) for i in range(3) for j in range(3)] def display(fields): for i in range(9): line = '' for j in range(9): if len(fields[9*i+j]) == 1: line += ' ' + str(fields[9*i+j][0]) else: line += ' ' print line def all(seq, pred=bool): "Returns True if pred(x) is True for every element in the iterable" for elem in ifilterfalse(pred, seq): return False return True def product(seq): prod = 1 for item in seq: prod *= item return prod def solve(problem): fields = [range(1,10) for i in range(81)] #fill with all posibilities for all fields for i,line in enumerate(problem): for j,letter in enumerate(line): if letter != ' ': fields[9*i+j]=[int(letter)] #seed with numbers from problem oldpos = 0 while True: pos = product(len(field) for field in fields) if pos == oldpos: #no new possibilities eliminated, so stop break display(fields) print pos,'possibilities' oldpos = pos for group in groups: for index in group: field = fields[index] if len(field) == 1: #if only number possible for field remove it from other fields in group for ind in group: if ind != index: try: fields[ind].remove(field[0]) except ValueError: pass else: #check if field contains number that does not exist in rest of group for f in field: if all(f not in fields[ind] \ for ind in group if ind!=index): fields[index] = [f] break -- http://mail.python.org/mailman/listinfo/python-list
Re: Brute force sudoku cracker
>> def all(seq, pred=bool): >What's this? What is bool? That came straight out of the manual for itertools: http://docs.python.org/lib/itertools-recipes.html -- http://mail.python.org/mailman/listinfo/python-list
real-time monitoring of propriety system: embedding python in C or embedding C in python?
Hi Group, at work, we are thinking to replace some legacy application, which is a home-grown scripting language for monitoring and controlling a large experiment. It is able to read live data from sensors, do some simple logic and calculations, send commands to other subsystems and finally generate some new signals. The way it is implemented is that it gets a chunk of 1 second of data (thousands of signals at sample rates from 1Hz to several kHz), does some simple calculations on selected signals, does some simple logic, sends some commands and finally computes some 1Hz output signals, all before the next chunk of data arrives. The purpose is mainly to monitor other fast processes and adjust things like process gains and set-points, like in a SCADA system. (I know about systems like Epics and Tango, but I cannot use those in the near future.) It can be considered soft-real time: it is desirable that the computation finishes within the next second most of the time, but if the deadline is missed occasionally, nothing bad should happen. The current system is hard to maintain and is limited in capabilities (no advanced math, no sub-functions, ...). I hope I don't have to convince you that python would be the perfect language to replace such a home-grown scripting language, especially since you than get all the power of tools like numpy, logging and interface to databases for free. Convincing my colleagues might cost some more effort, so I want to write a quick (and dirty?) demonstration project. Since all the functions I have to interface with (read and write of live data, sending commands, ...) are implemented in C, the solution will require writing both C and python. I have to choose between two architectures: A) Implement the main program in C. In a loop, get a chunk of data using direct call of C functions, convert data to python variables and call an embedded python interpreter that runs one iteration of the user's algorithm. When the script finishes, you read some variables from the interpreter and then call some other C-function to write the results. B) Implement the main loop in python. At the beginning of the loop, you call an embedded C function to get new data (using ctypes?), make the result readable from python (memoryview?), do the user's calculation and finally call another C function to write the result. Are there any advantages for using one method over the other? Note that I have more experience with python than with C. Thanks, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: baffled classes within a function namespace. Evaluation order.
On Thursday, April 25, 2013 11:27:37 PM UTC+2, Alastair Thompson wrote: > I am completely baffled by the behavior of this code with regards to the > evaluation order of namespaces when assigning the class attributes. Both > classes are nested within a function I called whywhywhy. [snip weird namespace problem] Hi, I am not a namespace expert, but I think the following example shows the same problem in an easier way without any classes, and gives a more helpful error message: In [1]: a = 123 In [2]: def f(): ...: print a ...: b = 456 In [3]: f() 123 In [4]: def g(): ...: print a ...: a = 456 In [5]: g() --- UnboundLocalError Traceback (most recent call last) /home/xxx/ in () > 1 g() /home/xxx/ in g() 1 def g(): > 2 print a 3 a = 456 4 UnboundLocalError: local variable 'a' referenced before assignment My guess is that in f(), the compiler sees no definition of a, so it assumes is must come from the outer namespace. In g(), however, it sees on the second line that a is uses as an assignment target, so it makes the variable a local. When it is executed, it rightfully complains that the local variable is not yet defined. A smarter compiler might prevent this problem, but then again a smarter programmer would not have local and global variables with the same name. In your example, something similar is probably happening, since you assign something to third inside example2, thereby making it 'local'. Since you are dealing with classes, the error message is probably not so clear (but whywhywhy would you define a class inside a function?) Does that make sense? HTH, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: Accessing next/prev element while for looping
Just make a custom generator function: >>> def prevcurnext(seq): it = iter(seq) prev = it.next() cur = it.next() for next in it: yield (prev,cur,next) prev,cur = cur, next >>> for (a,b,c) in prevcurnext(range(10)): print a,b,c 0 1 2 1 2 3 2 3 4 3 4 5 4 5 6 5 6 7 6 7 8 7 8 9 Cheers, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: Vector math library
I am not a regular user of the libraries that you mention, but I played around with some of them because I need a replacement for Matlab. Numeric, NumArray and SciPy should be more or less compatible. All the functions you mention should be in there, or otherwise should be trivial to implement. Have a look at the functions cross(), dot(), inner(), outer(). Addition is just a+b. As far as I know Numeric was the original vector lib. NumArray was written as a successor but ended up as a fork due to some speed concerns. Scipy is the latest and tries to unite the previous two by implementing the best of both worlds. For future work you should stick to SciPy. Right now it is probably somewhere in a beta stage, but expect a final version in half a year or so. Hopefully it ends up being THE vector lib for python to avoid confusing beginners like you. Cheers, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: important for me!!
Read this first: http://www.catb.org/~esr/faqs/smart-questions.html and then try again. -- http://mail.python.org/mailman/listinfo/python-list
Re: Try Python update
To expand on this idea: You could somehow combine the official tuturial (or any other good introductory text) and make all the examples in the text 'live'. Maybe use a split screen with the tutorial text on one side and the trypython console on the other. The newbie could then immediately try the example by typing it over himself or by clicking a button 'run in console' next to the example. Target audience should be only the real beginners who are afraid/too lazy to install the complete Python enviroment. Advanced users should be able to do a full install themselves. Cheers, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: Sudoku solver: reduction + brute force
There is more in this thread: http://groups.google.com/group/comp.lang.python/browse_frm/thread/479c1dc768f740a3/9252dab14e8ecabb?q=sudoku&rnum=2#9252dab14e8ecabb Enjoy, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: Arithmetic sequences in Python
I like the use of the colon as in the PEP better: it is consistant with the slice notation and also with the colon operator in Matlab. I like the general idea and I would probably use it a lot if available, but the functionality is already there with range and irange. Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: Math package
I think you need one of these: http://www-03.ibm.com/servers/deepcomputing/bluegene.html Don't know if it runs python. If that doesn't work try to reformulate your problem and have a look at http://scipy.org/ Cheers, Bas [EMAIL PROTECTED] wrote: > I want to write a program which would have a 2 dimensional array of 1 > billion by 1 billion. This is for computational purposes and evaluating > a mathematical concept similar to Erdos number. > > Which is the best package for such programs (that would be fast > enough). > > Every help is appreciated. > > Thanks -- http://mail.python.org/mailman/listinfo/python-list
Re: ratfun-2.3 Polynomials and Rational Functions
Are there any differences between this module and the one already present in numpy? http://www.scipy.org/doc/numpy_api_docs/numpy.lib.polynomial.html Cheers, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: comparing two arrays
You are comparing a normal python list to a constant, which are obviously unequal. Try converting your lists to arrays first (untested): import numeric/numpy as N a =N.array([0,1,2,5,6,6]) b = N.array([5,4,1,6,4,6]) print a==6 and b==6 print N.where(a==6 and b==6) hth, Bas Sheldon wrote: > Hi, > > I have two arrays that are identical and contain 1s and zeros. Only the > ones are valid and I need to know where both arrays have ones in the > same position. I thought logical_and would work but this example proves > otherwise: > >>> a = [0,1,2,5,6,6] > >>> b = [5,4,1,6,4,6] > >>> Numeric.logical_and(a==6,b==6) > 0 > >>> Numeric.where(a==b,1,0) > 0 > >>> Numeric.where(a==6 and b==6,1,0) > 0 > > The where() statement is also worhtless here. Does anyone have any > suggestion on how to do this? > > Thanks in advance, > Sheldon -- http://mail.python.org/mailman/listinfo/python-list
Re: returning index of minimum in a list of lists
[EMAIL PROTECTED] wrote: > Thanks so much for your help. I was wondering if there was anything > even simpler, but this will be great. >>> from numpy import * >>> a=array([[3,3,3,3], [3,3,3,1], [3,3,3,3]]) >>> where(a==a.min()) (array([1]), array([3])) Probably overkill for your simple problem, but this is a nice alternative if you do a lot of matrix work. Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: Numeric and matlab
Hi, I am also considering a switch from Matlab to NumPy/SciPy at some point. Note that in the last version of Matlab (7?) you don't have to use 'find', but you now can 'conditional arrays' as an index, so instead of idx=find(a>5); a(idx)=6; you can do: cond=a>5; a(cond) = 6; or even shorter a(a>5) = 6; Does someone know if the same trick is possible in NumPy? Cheers, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: a numarray question
I believe it is something like a[a==0] = 5 Note that numarray will eventually be replaced by Scipy/Numpy at some time, but this wouldn't change the basic stuff. Cheers, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: algorithm, optimization, or other problem?
Hi, as the others have already said, move all the invariants out of the loop. It is also not useful to randomly draw a vector out of random array. Some other small things: for i in range(len(x)): do something with x[i] should probably be replaced by for xi in x: do something with xi this saves an array index operation, don't know if this works for a numeric array You use the y**2 twice. A good compiler might notice this, but Python is interpreted... use += instead of + for w, the calculation can be done in place, this might save the creation of a new array/variable I am not sure what you are doing with x, bit it seems that you are transposing it a few times to many. Mightbe you can declare x as the transpose of what you do now, thereby saving the transpose in the loop? so my guess (not tested): x=random((1000,100))# 1000 input vectors, declared differently for xx in x: y=dot(xx,w) y2 = y*y w+=ETA*(y*xx-y2*w); th+= INV_TAU*(y2-th); Hope it helps, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: Matplotlib logarithmic scatter plot
Try this, don't know if this works for al versions: from pylab import * x=10**linspace(0,5,100) y=1/(1+x/1000) loglog(x,y) show() If you only need a logarithm along one axis you can use semilogx() or semilogy(). For more detailed questions go to the matplotlib mailing list. Cheers, Bas -- http://mail.python.org/mailman/listinfo/python-list
Is it possible to merge xrange and slice?
Hi, stupid question, but would it be possible to somehow merge xrange (which is supposed to replace range in py3k) and slice? Both have very similar start, stop and step arguments and both are lightweight objects to indicate a range. But you can't do a[xrange(10,20)] and 'for i in slice(10,20)'. The only difference is see is some behavior with infinities (e.g. object[3:] gives a slice(3,maxint) inside _getitem_ , but I think this should not be a large problem (xrange(0,infinity) could just yield a generator that never stops). Which problems am I overlooking that prevent this? Cheers, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: FM synthesis using Numpy
You got your math wrong. What you are calculating is: sin(2*pi*(1000+15*sin(2*pi*6*t))*t) = sin(2*pi*1000*t + 2*pi*15*sin(2*pi*6*t)*t) The 'instantaneous frequency' can be calculated by differentiating the argument of the sine and dividing by 2pi: x = sin(phi(t)) -> f_inst = d (phi(t)) / dt / (2*pi) So in your case: f_inst = 1000 + 15*sin(2*pi*6*t) + 2*pi*t*6*15*cos(2*pi*6*t) the last term explains the effect you hear. What you want is: f_inst = f0 + df*cos(2*pi*fm*t) Integrating this and multiplying by 2pi gives the phase: phi(t) = 2*pi*f0*t + sin(2*pi*fm*t)*df/fm So you can achieve the frequency modulation by using phase modulation (these two are related). You can do this with your own code by phi = oscillator(t, freq=6, amp=15/6) tone = oscillator(t, freq=1000, amp=0.1, phase=phi) cheers, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: a good explanation
I guess that your version is faster, although the difference would be negligible in this small example. The for loop is probably optimized for speed under the hood (it is written in C), while the 'while' loop is performed in python, which is much slower. Much more important than the speed difference is the clarity: your version is the accepted practice in the python world, so people will understand it immediately. It also saves two lines of code. And most of all, it prevents you from making mistakes: your friend, for example, has forgotten to increase cnt, so he created an infinite loop! Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: type-checking support in Python?
On Oct 7, 8:36 am, Lawrence D'Oliveiro <[EMAIL PROTECTED] central.gen.new_zealand> wrote: > In message <[EMAIL PROTECTED]>, Gabriel > > Genellina wrote: > > As an example, in the oil industry here in my country there is a mix of > > measurement units in common usage. Depth is measured in meters, but pump > > stroke in inches; loads in lbs but pressures in kg/cm². > > Isn't the right way to handle that to attach dimensions to each number? What they taught me as a physics undergrad is to always convert random units given as input to SI units as soon as possible, do all your calculations internally in SI units and (only if really needed) convert back to arbitrary units on output. Now, 15 years later, I am still trying to stick to this rule whenever possisble. This convention allows you to 'forget' about units and save your pre/post-fixes for the exceptional case: inch = 0.0254 lenght_inch = some_user_input_in_inch() length = length_inch * inch I have heard about some python package which overloads numbers and calculations to include units (quick google found unum, not sure if that is the only one). I guess that unless you are dealing with life- critical equipment or are using extreme programming, this is overkill (but I guess python is not really the right language for that anyway, imagine a garbage collection just when you want to launch your shuttle). Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: Need some advice
On Oct 21, 5:43 pm, azrael <[EMAIL PROTECTED]> wrote: > Need some advice I advice to come up with a more specific subject line for your posts, might give you some more answers -- http://mail.python.org/mailman/listinfo/python-list
Re: Plotting Graphs + Bestfit lines
I am not going to reverse engineer your code, but it looks like your writing your own least-squares fitting algorithm and doing some simple plots. Also, from your many posts last days, it looks like you are a newbie struggling with a python interface to gnuplot. May I suggest that you have a look at numpy/scipy/matplotlib instead? With those, the things that you are trying to do could be done trivially in a just a few lines. What you want to do could be done with something like (untested!): from pylab import * xdata = ... %whatever you get it from ydata = ... p = polyfit(xdata, ydata, 1) %fit 1st order polynomial plot(xdata, ydata, xdata, 'o', polyval(p, xdata)) %plot original data with fit show() Things like fitting algorithms are already included, so you can focus your energy on the real work. E.g., if you later want to change to a quadratic fit instead of a linear, you just change 1 to 2 in the polyfit. As you said in one of your other posts, you need to find the intersection point of two lines. If poly1 and poly2 are the polynomials describing the lines, you would get your answer as x_intersect = roots(poly1 - poly2) y_intersect = polyval(poly1,x_intersect) plot(x,polyval(poly1,x),x,polyval(poly2,x),x_intersect,y_intersect,'o') show() HTH, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: Profiling, sum-comprehension vs reduce
On Sep 13, 10:06 am, cnb <[EMAIL PROTECTED]> wrote: > This must be because of implementation right? Shouldn't reduce be > faster since it iterates once over the list? > doesnt sum first construct the list then sum it? No, sum also iterates the sequence just once and doesn't create a list. It is probably implemented similar to def sum(sequence, start=0): it = iter(sequence) total = start for i in it: total += i return i but then implemented in C for speed. Reduce is probably implemented pretty similar, but then with a random function instead of addition. Make sure that you understand the difference between generator expression and list comprehension, and that [f(x) for x in something] is (almost) equal to list(f(x) for x in something), so you can emulate a LC by using the list constructor on the equivalent GE. HTH, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: matrix algebra
On Sep 22, 10:02 am, Al Kabaila <[EMAIL PROTECTED]> wrote: > There are several packages for matrix algebra. I tried Numeric, numpy and > numarray. All three are very good, but each uses different syntax. That argument might have been valid 3 years ago, but as already said by others, Numeric and Numarray are deprecated. Numpy should be the only thing needed for new users. I suggest you investigate a little bit more the next time you make such efforts, since this fact should be widely known among the users of the mentioned packages, see e.g. the huge warning at the numarray page: http://www.stsci.edu/resources/software_hardware/numarray/numarray.html > 1. Is there any interest in matrix algebra "for the masses" (I mean interest > in a wrapper for a subset of functions of the packages with a unified > simple syntax)? In my opinion, no. I might be biased, since with my matlab background I find numpy simple enough as is. But I don't see how A = B*C+D or E=dot(F,G) is complicated for a beginner of linear algebra. > My OS is Linux (openSUSE 10.3) and my interest in retirement is Python > applications to Structural Analysis of Civil Engineering structures, > currently in 2 dimensions only (under GPL). Modern Structural Analysis is > highly matrix oriented, but requires only a few basic matrix operations, > namely matrix creation, transposition, multiplication, invertion and > linear equation solution. For stability analysis one would require > Eigenvalues and Eigenvectors. In 3 dimensions, additionally highly > desirable would be vector algebra. The packages do have all these > functions, but currently only the basic functions are in the wrapper. If you care about contributing something useful to the community, I think your time and skills are better spent writing some cool mechanical analysis tool for inclusion in Scipy. Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: Matplotlib Polar Plot Angles/Axes
I only have experience with the matlab version of polar, but my wild guess is that you have convert your degrees to radians. Go to the Matplotlib newsgroup if you need any better help. HTH, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: Matplotlib Polar Plot Angles/Axes
On Sep 26, 10:33 pm, afrogazer <[EMAIL PROTECTED]> wrote: > rad_angles = [elem*(pi/180) for elem in angles] You are missing some more on a friday afternoon: angles is created by arange, so it is a numpy array. In that case you simply can do rad_angles = pi/180 * angles No need to use list-comprehensions, that is the whole idea about using these kick-ass objects! Bas -- http://mail.python.org/mailman/listinfo/python-list
List of all syntactic sugar?
Hi group, just out of curiosity, is there a list of all the syntactic sugar that is used in python? If there isn't such a list, could it be put on a wiki somewhere? The bit of sugar that I do know have helped me a lot in understanding the inner workings of python. To give a few examples (might not be totally correct): x[i] -> x.__getitem__(i) x[a:b] -> x.__getitem__(slice(a,b,None)) x+y -> x._add__(y) x.method(a) -> call (x.__dict__[method], self, a) ?? for i in x: f(i) -> it = iter(x); while True: i = it.next(); f(i) except stop: pass TIA, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: List of all syntactic sugar?
>That kind of depends on what you mean by syntactic sugar. Mightbe I was misusing the name of syntactic sugar, but I what I intended to say was "all the possible 'transformations' that can be made to reduce all the 'advanced' syntax to some sort of minimal core of the language". Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: medians for degree measurements
On Jan 23, 1:09 am, Steve Howell wrote: [snip problem with angle data wrapping around at 360 degrees] Hi, This problem is trivial to solve if you can assume that you that your data points are measured consecutively and that your boat does not turn by more than 180 degrees between two samples, which seems a reasonable use case. If you cannot make this assumption, the answer seems pretty arbitrary to me anyhow. The standard trick in this situation is to 'unwrap' the data (fix > 180 deg jumps by adding or subtracting 360 to subsequent points), do your thing and then 'rewrap' to your desired interval ([0-355] or [-180,179] degrees). In [1]: from numpy import * In [2]: def median_degree(degrees): ...: return mod(rad2deg(median(unwrap(deg2rad(degrees,360) ...: In [3]: print(median_degree([1, 2, 3, 4, 5, 6, 359])) 3.0 In [4]: print(median_degree([-179, 174, 175, 176, 177, 178, 179])) 177.0 If the deg2rad and rad2deg bothers you, you should write your own unwrap function that handles data in degrees. Hope this helps, Bas P.S. Slightly off-topic rant against both numpy and matlab implementation of unwrap: They always assume data is in radians. There is some option to specify the maximum jump size in radians, but to me it would be more useful to specify the interval of a complete cycle, so that you can do unwrapped_radians = unwrap(radians) unwrapped_degrees = unwrap(degrees, 360) unwrapped_32bit_counter = unwrap(overflowing_counter, 2**32) -- http://mail.python.org/mailman/listinfo/python-list
Re: medians for degree measurements
> On 2010-01-25 10:16 AM, Bas wrote: > > > P.S. > > Slightly off-topic rant against both numpy and matlab implementation > > of unwrap: They always assume data is in radians. There is some option > > to specify the maximum jump size in radians, but to me it would be > > more useful to specify the interval of a complete cycle, so that you > > can do > > > unwrapped_radians = unwrap(radians) > > unwrapped_degrees = unwrap(degrees, 360) > > unwrapped_32bit_counter = unwrap(overflowing_counter, 2**32) On Jan 25, 5:34 pm, Robert Kern wrote:> > Rants accompanied with patches are more effective. :-) As you wish (untested): def unwrap(p, cycle=2*pi, axis=-1): """docstring to be updated""" p = asarray(p) half_cycle = cycle / 2 nd = len(p.shape) dd = diff(p, axis=axis) slice1 = [slice(None, None)]*nd # full slices slice1[axis] = slice(1, None) ddmod = mod(dd+half_cycle, cycle)-half_cycle _nx.putmask(ddmod, (ddmod==-half_cycle) & (dd > 0), half_cycle) ph_correct = ddmod - dd; _nx.putmask(ph_correct, abs(dd)http://mail.python.org/mailman/listinfo/python-list
Re: medians for degree measurements
> >> On 2010-01-25 10:16 AM, Bas wrote: > >>> P.S. > >>> Slightly off-topic rant against both numpy and matlab implementation > >>> of unwrap: They always assume data is in radians. There is some option > >>> to specify the maximum jump size in radians, but to me it would be > >>> more useful to specify the interval of a complete cycle, so that you > >>> can do [snip] > > I never saw a use case for the discontinuity argument, so in my > > preferred version it would be removed. Of course this breaks old code > > (by who uses this option anyhow??) and breaks compatibility between > > matlab and numpy. On Jan 25, 6:39 pm, Robert Kern wrote: > Sometimes legitimate features have phase discontinuities greater than pi. We are dwelling more and more off-topic here, but anyhow: According to me, the use of unwrap is inherently related to measurement instruments that wrap around, like rotation encoders, interferometers or up/down counters. Say you have a real phase step of +1.5 pi, how could you possibly discern if from a real phase step of -pi/2? This is like an aliasing problem, so the only real solution would be to increase the sampling speed of your system. To me, the discontinuity parameter is serving some hard to explain corner case (see matlab manual), which is better left to be solved by hand in cases it appears. I regret matlab ever added the feature. > If you want your feature to be accepted, please submit a patch that does not > break > backwards compatibility and which updates the docstring and tests > appropriately. > I look forward to seeing the complete patch! Thank you. I think my 'cycle' argument does have real uses, like the degrees in this thread and the digital-counter example (which comes from own experience and required me to write my own unwrap). I'll try to submit a non-breaking patch if I ever have time. Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: getting properly one subprocess output
On Nov 18, 12:25 pm, Jean-Michel Pichavant
wrote:
> Hi python fellows,
>
> I'm currently inspecting my Linux process list, trying to parse it in
> order to get one particular process (and kill it).
> I ran into an annoying issue:
> The stdout display is somehow truncated (maybe a terminal length issue,
> I don't know), breaking my parsing.
Below is the script I use to automatically kill firefox if it is not
behaving, maybe you are looking for something similar.
HTH,
Bas
#!/usr/bin/env python
import commands, os
lines = os.popen('ps ax|grep firefox').readlines()
lines = [line for line in lines if 'grep' not in line]
print lines[0]
pid = int(lines[0][:5])
print 'Found pid: %d' %pid
os.system('kill -9 %d' %pid)
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Re: lambda with floats
On Apr 7, 6:15 am, Patrick Maupin wrote: > I should stop making a habit of responding to myself, BUT. This isn't > quite an acre in square feet. I just saw the 43xxx and assumed it > was, and then realized it couldn't be, because it wasn't divisible by > 10. (I used to measure land with my grandfather with a 66 foot long > chain, and learned at an early age that an acre was 1 chain by 10 > chains, or 66 * 66 * 10 = 43560 sqft.) > That's an exact number, and 208 is a poor approximation of its square > root. There is no need to remember those numbers for the imperially challenged people: In [1]: import scipy.constants as c In [2]: def acre2sqft(a): ...: return a * c.acre / (c.foot * c.foot) ...: In [3]: acre2sqft(1) Out[3]: 43560.0 Cheers, Bas -- http://mail.python.org/mailman/listinfo/python-list
Re: Too much code - slicing
On Sep 17, 10:01 pm, Andreas Waldenburger
wrote:
> On Thu, 16 Sep 2010 16:20:33 -0400 AK wrote:
>
> > I also like this construct that works, I think, since 2.6:
>
> > code = dir[int(num):] if side == 'l' else dir[:-1*int(num)]
>
> I wonder when this construct will finally start to look good.
Using IFs is just plain ugly. Why not go for the much more pythonic
code = (lambda s:dir[slice(*(s*int(num),None)[::s])])(cmp('o',side))
Much easier on the eyes and no code duplication ... ;)
Bas
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Obj.'s writing self-regeneration script ?
Hello, Is there a good/standard way of having (composite) objects write a Python script which will regenerate the very same object ? This problem arises when I construct, for example, a "ComputationalProblem" object, possibly through an object editor GUI, importing data structures from external geometric and material modelers etc. Once the object has been constructed, one wants to write it to a file on disk, for example to do the computations later on. In order to help users, familiar with the (in)famous "input-file monolithic-code output-file" sequence I would like to have this diskfile take the form of recognisable and editable Python code (instead of a "dump" solution with Pickle for example). I think there are problems with uniqueness and ordering of the component instantiations. I was thinking of something like a depth-first recursive write-script() on the object's attributes using the __class__ 's to construct generic names for the instantiations. Has anyone given this a thought already ? Thank you in advance for any remarks, -- Bas Michielsen ONERA, Electromagnetics and Radar Department 2, avenue Edouard Belin, 31055 TOULOUSE cedex, France Tel. (++33)(0)5 62 25 26 77 Fax. (++33)(0)5 62 25 25 77 -- http://mail.python.org/mailman/listinfo/python-list
Re: Obj.'s writing self-regeneration script ?
Jerome Alet wrote: > Hi, > > Le Fri, 08 Jul 2005 15:16:21 +0200, Bas Michielsen a écrit : > > >>Is there a good/standard way of having (composite) >>objects write a Python script which will regenerate >>the very same object ? > > > I've done something like this for the ReportLab toolkit. > > Last time I checked, this was still part of the project under > the name "pycanvas". You use a pycanvas.Canvas() instance > just like you would use a canvas.Canvas() instance, but you can decide to > regenerate an equivalent Python source program to your original program > when rendering. > > The docstring explains how to use it. Also > reportlab/test/test_pdfgen_pycanvas.py shows if it works or not. > > NB : this is not generic code, but maybe this can help you. > > bye > > Jerome Alet Thank you very much, I will have a look at it. Bas -- Bas Michielsen ONERA, Electromagnetics and Radar Department 2, avenue Edouard Belin, 31055 TOULOUSE cedex, France Tel. (++33)(0)5 62 25 26 77 Fax. (++33)(0)5 62 25 25 77 -- http://mail.python.org/mailman/listinfo/python-list
Re: emulate a serial port in windows (create a virtual 'com' port)
On Jan 30, 7:34 am, Pom <[EMAIL PROTECTED]> wrote: > how can I emulate a serial port in windows? Google for ComEmulDrv3 This may do what you want. -- http://mail.python.org/mailman/listinfo/python-list
Re: Using SWIG to build C++ extension
mk wrote:
> Hello,
>
> I'm having terrible problems building C++ extension to Python 2.4 using
> SWIG. I'd appreciate if somebody knowledgeable at the subject took a
> look at it. swig-1.3.29, g++ (GCC) 4.1.1 20070105 (Red Hat 4.1.1-52).
>
> I used following commands to build C++ extension:
>
> # swig -c++ -python edit_distance.i
> # c++ -c edit_distance.c edit_distance_wrap.cxx edit_distance.cpp -I.
> -I/usr/include/python2.4
>
>
> Linux RH (9.156.44.105) root ~/tmp # c++ -c edit_distance.c
> edit_distance_wrap.cxx edit_distance.cpp -I. -I/usr/include/python2.4
> c++: edit_distance.cpp: No such file or directory
> edit_distance_wrap.cxx: In function ‘PyObject*
> _wrap_edit_distance(PyObject*, PyObject*)’:
> edit_distance_wrap.cxx:2579: error: ‘string’ was not declared in this
> scope edit_distance_wrap.cxx:2579: error: ‘arg1’ was not declared in this
> scope edit_distance_wrap.cxx:2580: error: ‘arg2’ was not declared in this
> scope edit_distance_wrap.cxx:2597: error: expected type-specifier before
> ‘string’ edit_distance_wrap.cxx:2597: error: expected `>' before ‘string’
> edit_distance_wrap.cxx:2597: error: expected `(' before ‘string’
> edit_distance_wrap.cxx:2597: error: expected primary-expression before
> ‘>’ token
> edit_distance_wrap.cxx:2597: error: expected `)' before ‘;’ token
> edit_distance_wrap.cxx:2605: error: expected type-specifier before
> ‘string’ edit_distance_wrap.cxx:2605: error: expected `>' before ‘string’
> edit_distance_wrap.cxx:2605: error: expected `(' before ‘string’
> edit_distance_wrap.cxx:2605: error: expected primary-expression before
> ‘>’ token
> edit_distance_wrap.cxx:2605: error: expected `)' before ‘;’ token
>
> What's weird is that I _did_ use std:: namespace prefix carefully in the
> code:
>
> #include
> #include
> #include
>
> const unsigned int cost_del = 1;
> const unsigned int cost_ins = 1;
> const unsigned int cost_sub = 1;
>
>
> unsigned int edit_distance( std::string& s1, std::string& s2 )
> {
> const size_t len1 = s1.length(), len2 = s2.length();
> std::vector > d(len1 + 1,
> std::vector(len2 + 1));
>
> for(int i = 1; i <= len1; ++i)
> for(int j = 1; j <= len2; ++j)
> d[i][j] = std::min(d[i - 1][j] + 1,
> std::min(d[i][j - 1] + 1, d[i - 1][j - 1] + (s1[i - 1] == s2[j - 1] ? 0
> : 1)));
>
> return d[len1][len2];
> }
>
> Ok, anyway I fixed it in the generated code (edit_distance_wrap.cxx). It
> compiled to .o file fine then. It linked to _edit_distance.so as well:
>
> # c++ -shared edit_distance_wrap.o -o _edit_distance.so
>
> But now I get import error in Python!
>
> Linux RH root ~/tmp # python
> Python 2.4.3 (#1, Dec 11 2006, 11:38:52)
> [GCC 4.1.1 20061130 (Red Hat 4.1.1-43)] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
> >>> import edit_distance
> Traceback (most recent call last):
>File "", line 1, in ?
>File "edit_distance.py", line 5, in ?
> import _edit_distance
> ImportError: ./_edit_distance.so: undefined symbol: _Z13edit_distanceRSsS_
>
>
>
> What did I do to deserve this? :-)
>
>
> edit_distance.i file just in case:
>
> %module edit_distance
> %{
> #include "edit_distance.h"
> %}
>
> extern unsigned int edit_distance(string& s1, string& s2);
Hello,
I took your example files and did the following:
changed the #include "edit_distance.h" to #include "edit_distance.c"
in the edit_distance.i file.
Then I changed the first few lines of your function definition
unsigned int edit_distance( const char* c1, const char* c2 )
{
std::string s1( c1), s2( c2);
and also adapted the signature in the edit_distance.i file.
Then
swig -shadow -c++ -python edit_distance.i
g++ -c -fpic -I/usr/include/python edit_distance_wrap.cxx
g++ -shared edit_distance_wrap.o -o _edit_distance.so
I could import edit_distance without any error messages
>>> import edit_distance
>>> print edit_distance.edit_distance( "toto", "titi")
2
>>> print edit_distance.edit_distance( "toto", "toti")
1
Perhaps I changed too many things, but this may get you started,
Regards,
Bas
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pytone / _bsddb
Hi all, I've been using the `pytone' tool for playing my mp3's for a while. Great tool. However, after upgrading Python to version 2.4 it stopped working. The traceback that I get is this: -- Traceback (most recent call last): File "src/pytone.py", line 104, in ? songdbid = songdbmanager.addsongdb(songdbname, +config.database[songdbname]) File "/home/basvg/bin/PyTone-2.2.1/src/services/songdb.py", line 147, in +addsongdb import songdbs.local File "/home/basvg/bin/PyTone-2.2.1/src/services/songdbs/local.py", line +24, in ? import bsddb.dbshelve File "/usr/lib/python2.4/bsddb/__init__.py", line 47, in ? import _bsddb ImportError: No module named _bsddb -- The mentioned line in __init__.py is: -- import _bsddb -- I had a look around through /usr/lib/python2.4 but I couldn't find a _bsddb indeed. Can anyone help me get my favorite py-tool to work again ;-)? Bas -- <[EMAIL PROTECTED]> - GPG Key ID: 2768A493 - http://www.cs.ru.nl/~basvg Radboud University Nijmegen Institute for Computing and Information Sciences -- http://mail.python.org/mailman/listinfo/python-list
Re: pytone / _bsddb
On 2005-03-03, Bas van Gils <[EMAIL PROTECTED]> wrote: > Hi all, > > I've been using the `pytone' tool for playing my mp3's for a while. Great > tool. However, after upgrading Python to version 2.4 it stopped working. The > traceback that I get is this: [ ... ] Great, I found it myself. The problem was a version of db that was `too new'. Apparently Python didn't like this version of db. After downgrading it and rebuilding Python everything worked as expected. Yay! Bas -- <[EMAIL PROTECTED]> - GPG Key ID: 2768A493 - http://www.cs.ru.nl/~basvg Radboud University Nijmegen Institute for Computing and Information Sciences -- http://mail.python.org/mailman/listinfo/python-list
OrderedEnum examples
Using the enum34 0.9.13 package from PyPi in Python 2.7.3, the examples for OrderedEnum seem to be broken. The example in the package documentation reads: class OrderedEnum(Enum): def __ge__(self, other): if self.__class__ is other.__class__: return self._value >= other._value return NotImplemented def __gt__(self, other): if self.__class__ is other.__class__: return self._value > other._value return NotImplemented def __le__(self, other): if self.__class__ is other.__class__: return self._value <= other._value return NotImplemented def __lt__(self, other): if self.__class__ is other.__class__: return self._value < other._value return NotImplemented class Grade(OrderedEnum): __ordered__ = 'A B C D F' A = 5 B = 4 C = 3 D = 2 F = 1 Grade.C < Grade.A to which Python replies with: Traceback (most recent call last): File "test.py", line 35, in print Grade.C < Grade.A File "test.py", line 23, in __lt__ return self._value < other._value AttributeError: 'Grade' object has no attribute '_value' Also, in the example in the Python 3.4 library documentation (section 8.17.2) has the __ordered__ attribute removed (presumably because, in contrast to Python 2.x, Python 3 will respect the order of attribute definition). This example gives the same ValueErrror when using the enum34 package in Python 2.7.3. It is the same example, after all. Replacing each occurrence of self._value with either self._value_ or self.value in the examples seems to make them work as expected. Are both examples incorrect, or not intended to work in Python 2.x? -- S. van der Wulp -- http://mail.python.org/mailman/listinfo/python-list
Re: OrderedEnum examples
On 30-7-2013 21:30, Ethan Furman wrote: On 07/30/2013 11:58 AM, Ian Kelly wrote: On Tue, Jul 30, 2013 at 12:18 PM, Bas van der Wulp wrote: Replacing each occurrence of self._value with either self._value_ or self.value in the examples seems to make them work as expected. Are both examples incorrect, or not intended to work in Python 2.x? The _value attribute was renamed _value_ in: http://hg.python.org/cpython/rev/511c4daac102 It looks like the example wasn't updated to match. You should probably just use self.value here since the name of the private attribute is an implementation detail. In `__new__` it has to be `_value_`, but in the other methods `.value` works fine. Updated the 3.4 example with `.value`. -- ~Ethan~ That was quick! Thanks Ethan and Ian. Regards, Bas -- http://mail.python.org/mailman/listinfo/python-list
