🌐 Mailman 3 November 2007 - Python-list - python.org

PyDict_*() refcount assumptions
by sndive＠gmail.com Nov. 1, 2007

Nov. 1, 2007

i checked this: http://svn.python.org/projects/python/trunk/Doc/data/refcounts.dat and it seems that PyDict_SetItem incref the value being added and the key and PyDict_DelItem does not decrement any refcounts so i have to do so manually for the key and for the data( by calling PyDict_GetItem first). Did i decipher the dat file correctly and is there a wrapper for DelItem that reverses the refcounts to what they were before the SetItem or do i have have to do 2 calls for deletion?

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jpeg image read class
by devnew＠gmail.com Nov. 1, 2007

Nov. 1, 2007

hi i am new to python and PIL and was trying to write a class to read and write RGB color model jpeg images.. i came up with this class below..i want to know if this is the way to read/write the RGB color model jpeg..if anyone can give feedback (esp on the methods writeImage1( ) and writeImage2( ) it wd help my studies .. TIA dn #jpgpy.py import Image from sys import argv from numpy import array class JPGFile: def __init__(self,filename): self._filename=filename self._height=0 self._width=0 self._mode="" self._rgblist=[] self._pixellist=[] self._pixarray=None self.readImage() def getheight(self): return self._height def getwidth(self): return self._width def getpixellist(self): return self._pixellist def getrgblist(self): return self._rgblist def makepixval(self,(r,g,b)): alpha=255 pixval=(alpha<<24)|(r<<16 )|( g<<8) | b return pixval def readImage(self): im=Image.open(self._filename) self._mode=im.mode self._width,self._height=im.size for y in range(self._height): for x in range(self._width): r,g,b=im.getpixel((x,y)) self._rgblist.append((r,g,b)) pval=self.makepixval((r,g,b)) self._pixellist.append(pval) self._pixarray=array(self._pixellist,float) def makergb(self,pixval): alpha=pixval>>24 red=(pixval>>16 )&255 green=(pixval>>8 )&255 blue=(pixval)& 255 return red,green,blue def writeImage1(self,fname,data,width,height): imnew=Image.new(self._mode,(width,height)) newrgblist=[] for i in range(len(data)): r,g,b=self.makergb(data[i]) newrgblist.append((r,g,b)) index=0 for y in range(height): for x in range(width): imnew.putpixel((x,y),newrgblist[index]) index+=1 imnew.save(fname) def writeImage2(self,fname,data,width,height): imnew=Image.new(self._mode,(width,height)) newrgblist=[] for i in range(len(data)): r,g,b=self.makergb(data[i]) newrgblist.append((r,g,b)) imnew.putdata(newrgblist) imnew.save(fname) imgname=argv[1] #Usage: python jpgpy.py myimage.jpg print "to read from:",imgname x=JPGFile(imgname) print x.getheight(),"",x.getwidth() pixlist=x.getpixellist() rgbtpllist=x.getrgblist() w=x.getwidth() h=x.getheight() x.writeImage1("newimage1.jpg",pixlist,w,h)

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Re: capturing output of command line in an array
by amjadcsu＠gmail.com Nov. 1, 2007

Nov. 1, 2007

thanks Lee, I would just like to get the "node" in that list. so it would be something like this alist=[node13,node12,node8,node2,node1.....] I dont want the whole info is it possible?? On Oct 31, 9:44 am, Lee Capps <lca...(a)cteresource.org> wrote: > On Oct 31, 2007, at 11:01 AM, amjad...(a)gmail.com wrote: > > > > > I am trying to execute a command using os.system. this command lists > > the number of nodes alive in a cluster. I would like to capture the > > output in list/array in python. IS it possible.?/ > > > Here is my command > > gstat -a > > node13 2 ( 0/ 56) [ 0.00, 0.00, 0.00] [ 0.0, 0.0, > > 0.1, 99.9, 0.0] OFF > > node12 2 ( 1/ 63) [ 0.99, 0.97, 0.91] [ 46.6, 0.0, > > 3.7, 49.8, 0.0] OFF > > node8 2 ( 1/ 59) [ 0.99, 0.97, 0.91] [ 47.5, 0.0, > > 2.8, 49.7, 0.0] OFF > > node2 2 ( 1/ 59) [ 0.99, 0.97, 0.91] [ 46.6, 0.0, > > 3.7, 49.7, 0.0] OFF > > node1 2 ( 1/ 59) [ 0.99, 0.97, 0.91] [ 46.6, 0.0, > > 3.7, 49.7, 0.0] OFF > > node7 2 ( 1/ 58) [ 0.99, 0.97, 0.91] [ 49.8, 0.0, > > 0.6, 49.7, 0.0] OFF > > node11 2 ( 1/ 59) [ 0.99, 0.97, 0.91] [ 46.6, 0.0, > > 3.8, 49.6, 0.0] OFF > > node4 2 ( 1/ 59) [ 1.00, 1.00, 0.93] [ 46.6, 0.0, > > 3.7, 49.7, 0.0] OFF > > node10 2 ( 1/ 59) [ 1.00, 1.00, 0.94] [ 46.7, 0.0, > > 3.7, 49.7, 0.0] OFF > > node5 2 ( 1/ 59) [ 1.00, 1.00, 0.92] [ 49.8, 0.0, > > 0.4, 49.7, 0.0] OFF > > node6 2 ( 1/ 59) [ 1.00, 1.00, 0.94] [ 49.5, 0.0, > > 0.9, 49.7, 0.0] OFF > > > I would like to have an array where each element contains the nodes > > > for example > > a=[node13,node12,node2,node8,node1,node7,node 11] > > > any help would be appreciated > > You might try os.popen to read in the output of your command. > > It would be helpful to have more information about what you'd like to > do with your list. Do you just want to put the text of the > individual node lines from gstat into the list? If so, os.popen > should work for you. Or do you need to parse the lines and store > them in, say dictionaries? Tuples? If you need to parse it, you > could use module re, or even just string methods, depending on what > you're trying to do . . . . > > HTH, > > --- > Lee Capps > Technology Specialist > CTE Resource Center > lca...(a)cteresource.org

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XML DOM, but in chunks
by Sean Davis Nov. 1, 2007

Nov. 1, 2007

I have some very large XML files that are basically recordsets. I would like to access each record, one-at-a-time, and I particularly like the ElementTree library for accessing the data. Is there a way to have ElementTree read only one record of the data at a time? Alternatively, are there other ways that would allow one to parse out a record at a time and maintain some nice ways of accessing the elements within the record? Thanks, Sean

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Re: capturing output of command line in an array
by amjadcsu＠gmail.com Nov. 1, 2007

Nov. 1, 2007

Thanks Lee I am looking to just get the node name from that info. I dont need all other info so my list would be just alist=[node13,node12,node8,node1 ....] is it possible?? On Oct 31, 9:44 am, Lee Capps <lca...(a)cteresource.org> wrote: > On Oct 31, 2007, at 11:01 AM, amjad...(a)gmail.com wrote: > > > > > I am trying to execute a command using os.system. this command lists > > the number of nodes alive in a cluster. I would like to capture the > > output in list/array in python. IS it possible.?/ > > > Here is my command > > gstat -a > > node13 2 ( 0/ 56) [ 0.00, 0.00, 0.00] [ 0.0, 0.0, > > 0.1, 99.9, 0.0] OFF > > node12 2 ( 1/ 63) [ 0.99, 0.97, 0.91] [ 46.6, 0.0, > > 3.7, 49.8, 0.0] OFF > > node8 2 ( 1/ 59) [ 0.99, 0.97, 0.91] [ 47.5, 0.0, > > 2.8, 49.7, 0.0] OFF > > node2 2 ( 1/ 59) [ 0.99, 0.97, 0.91] [ 46.6, 0.0, > > 3.7, 49.7, 0.0] OFF > > node1 2 ( 1/ 59) [ 0.99, 0.97, 0.91] [ 46.6, 0.0, > > 3.7, 49.7, 0.0] OFF > > node7 2 ( 1/ 58) [ 0.99, 0.97, 0.91] [ 49.8, 0.0, > > 0.6, 49.7, 0.0] OFF > > node11 2 ( 1/ 59) [ 0.99, 0.97, 0.91] [ 46.6, 0.0, > > 3.8, 49.6, 0.0] OFF > > node4 2 ( 1/ 59) [ 1.00, 1.00, 0.93] [ 46.6, 0.0, > > 3.7, 49.7, 0.0] OFF > > node10 2 ( 1/ 59) [ 1.00, 1.00, 0.94] [ 46.7, 0.0, > > 3.7, 49.7, 0.0] OFF > > node5 2 ( 1/ 59) [ 1.00, 1.00, 0.92] [ 49.8, 0.0, > > 0.4, 49.7, 0.0] OFF > > node6 2 ( 1/ 59) [ 1.00, 1.00, 0.94] [ 49.5, 0.0, > > 0.9, 49.7, 0.0] OFF > > > I would like to have an array where each element contains the nodes > > > for example > > a=[node13,node12,node2,node8,node1,node7,node 11] > > > any help would be appreciated > > You might try os.popen to read in the output of your command. > > It would be helpful to have more information about what you'd like to > do with your list. Do you just want to put the text of the > individual node lines from gstat into the list? If so, os.popen > should work for you. Or do you need to parse the lines and store > them in, say dictionaries? Tuples? If you need to parse it, you > could use module re, or even just string methods, depending on what > you're trying to do . . . . > > HTH, > > --- > Lee Capps > Technology Specialist > CTE Resource Center > lca...(a)cteresource.org

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Re: object inheritance
by Anand Nov. 1, 2007

Nov. 1, 2007

On Oct 31, 9:57 am, "Gabriel Genellina" <gagsl-...(a)yahoo.com.ar> wrote: > En Wed, 31 Oct 2007 00:36:34 -0300, Anand <anandol...(a)gmail.com> escribi�: > > >> No, that is an argument for multiple-inheritance, mixin classes etc. You > >> know when constructing the object what behaviour you want it to have. It > >> isn't an argument for changing the behaviour of an existing object > >> dynamically. > > Partially true. I don't want to change the behavior of an exiting > > object. I know what behavior I want to have at the time of creating. > > This can be achieved by creating classes dynamically by parameterizing > > the base class, which I thought is ugly. > > If you know at compile time which features you want, you can use multiple > inheritance to define the new class. > If you only know the set of clases to mix at run time, you can dinamically > create new classes with 'type': > > newclass = type('newclass', (CachedDB, SimpleDB), {}) > db = newclass() > db.withIDs will call CachedDB.withID, as you want. Interesting. CachedDB.withID should call withID from its super class (here SimpleDB), when it is not in cache. How to do that?

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Endless GIL and thread confusion
by enska Nov. 1, 2007

Nov. 1, 2007

Can someone clarify the steps needed to make access to the interpreter safe from multiple threads? I've been reading the docs for days and I still find them very confusing and misleading. For example does the PyGILState_Ensure() function lock the GIL or just create the thread state? Is thread supposed to call it once on creation and then the release function before exiting or is this the preferred mechanism to handle the locking? Most of the confusion stems from this segment in the documentation. "...when threads are created from C, they don't have the global interpreter lock, nor is there a thread state data structure for them. Such threads must bootstrap themselves into existence, by first creating a thread state data structure, then acquiring the lock, and finally storing their thread state pointer, before they can start using the Python/C API. When they are done, they should reset the thread state pointer, release the lock, and finally free their thread state data structure. Beginning with version 2.3, threads can now take advantage of the PyGILState_*() functions to do all of the above automatically." Anyway, currently my code looks like this: void foobar(...) { PyGILState state = PyGILState_Ensure(); // make python calls PyGILState_Release(state); } void blablah(...) { PyGILState state = PyGILState_Ensure(); // make python calls PyGILState_Release(state); } My python Initialization code looks like this void init_python(char* progname, char* bindir) { Py_SetProgramName(progname); PyEval_InitThreads(); Py_InitializeEx(0); char* argv[] = {progname, bindir}; PySys_SetArgv(2, argv); } calling foobar() or blablah() from the main thread works as expected, but if the second thread calls them it locks up in the call to PyGILState_Ensure(). I have tried adding a call to PyEval_ReleaseLock() in the init_python function to make sure that the main thread is not holding the GIL, but this causes the application to segfault when it is calling Py_Finalize() so it is clear that this is not correct. Please advice. Thanks.

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Re: a few questions.
by Larry Bates Nov. 1, 2007

Nov. 1, 2007

Shawn Minisall wrote: > 1. whats the best way to round a result to 4 decimal places? > > I tried round, but then read that it only works with exponents of 10. > > I'm trying to do it on this piece of code. > > time = (distance / 4900) > > 2. What direction would I go in if I'm getting 5 inputs from the user > and want to make a bar table out of them where a * represents a 100 of > the total number? > > For example, > > Store 1: * * > > Store 2: * > > Store 3: * * * > > ect, > > I already know I'm going to be expecting to use a for loop (0,4) since > there are 5 inputs, but how to get from say, 200 to the output of * * > I'm a little lost. > > thx > > > Q:1 >>> round(123.45678, 4) 123.4568 Q2: Something like this works: stores=[] for i in xrange(0,5): x=raw_input("input number for store=%i ?" % i) stores.append(int(x)) for i in xrange(0,5): hundreds, remainder=divmod(stores[i], 100) print "Store: %i %s" % (i+1, hundreds*"*") -Larry

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