[noob question] References and copying
Hello! Where can I find a good explanation when does an interpreter copy the value, and when does it create the reference. I thought I understand it, but I have just typed in following commands: >>> a=[[1,2],[3,4]] >>> b=a[1] >>> b=[5,6] >>> a [[1, 2], [3, 4]] >>> b [5, 6] And I don't understand it. I thought, that b will be a reference to a, so changing b should change a as well. What do I do wrong. And a second question - can I create a reference to element of a list of floating points and use this reference to change that element? Greets to all PyFans zefciu -- http://mail.python.org/mailman/listinfo/python-list
Reuseable iterators - which is better?
In the tutorial there is an example iterator class that revesrses the string given to the constructor. The problem is that this class works only once, unlike built-in types like string. How to modify it that it could work several times? I have tried two approaches. They both work, but which of them is stylistically better? class Reverse: #original one "Iterator for looping over a sequence backwards" def __init__(self, data): self.data = data self.index = len(data) def __iter__(self): return self def next(self): if self.index == 0: raise StopIteration self.index = self.index - 1 return self.data[self.index] class Reverse: #1st approach "Reuseable Iterator for looping over a sequence backwards" def __init__(self, data): self.data = data self.index = len(data) def __iter__(self): return self def next(self): if self.index == 0: self.index = len(self.data) #Reset when previous # iterator goes out raise StopIteration self.index = self.index - 1 return self.data[self.index] class Reverse: #2nd approach "Reuseable Iterator for looping over a sequence backwards" def __init__(self, data): self.data = data def __iter__(self): self.index = len(self.data) #Reset as a part of iterator # creation return self def next(self): if self.index == 0: raise StopIteration self.index = self.index - 1 return self.data[self.index] -- http://mail.python.org/mailman/listinfo/python-list
Re: How to run Python file?
Pontus Ekberg wrote: > mistral wrote: > >> I have installed ActivePython >> http://www.activestate.com/Products/ActivePython/ >> How I can run Python file, test.py? > > $ python test.py > > or > > $ ./test.py (if test.py is executable) > > Thats if you use un*x. If you word under windows, the first would work, but rather use some IDE like IDLE or SPE than mess with the windows command line. Then you just load the file and run it from the menu. zefciu -- http://mail.python.org/mailman/listinfo/python-list
Inheritance doesn't work
I have a problem with inheritance under python. The class definition is longer, but the troublesome thing is: from PIL import Image class MandelbrotImage (Image): pass I am getting the following error: Traceback (most recent call last): File "", line 1, in ? File "mandelimage.py", line 3, in ? class MandelImage (Image): TypeError: Error when calling the metaclass bases module.__init__() takes at most 2 arguments (3 given) I am using python 2.4 from the Debian (Sid) packages. Is it a bug, or am I doing something wrong? zefciu -- -BEGIN zefciu's GEEK CODE BLOCK- Version: 3.12 GS d-(+) s+++:-- a-- C++ UL P- L++(+++) E--- W+ N++ o? K? w-- M- V? PS-(--) PE++(+) Y PGP+ t 5 X R tv- b++ DI D- G e>+++ h!>-- y? UF+ --END zefciu's GEEK CODE BLOCK-- -- http://mail.python.org/mailman/listinfo/python-list
Re: Converting a c array to python list
I have just read about buffer and array objects and I think one of them could be fit for my need. However there are two questions. If i make a buffer from a part of dynamically allocated memory, what would free it? Should it be allocated with malloc or some python-specific function? How on earth can I create array object in C? zefciu -- http://mail.python.org/mailman/listinfo/python-list
Re: Converting a c array to python list
Russell E. Owen wrote: > > It might help to have a clearer idea of why you want to do this. > I am writing a Mandelbrot fractal generator with Tkinter interface. Now the generation works like this - there is a loop in python which iterates through fractal's pixels and for each of them calls a functions which checks if it belongs to Mandelbrot set or how many iterations does it take for this point to bail out. Then the python function sets the pixel's colour according to the result. I was testing it first with python function, written rather for readibility not speed, using the builtin complex class. It took about 90 s to generate a 1152x864 fractal. Then I used a c function and it took 14 s. When I told it to my friend (grad student of informatics) he said "And probably 90% of the time takes calling the function". So I think, that maybe I should put the whole loop into c code. But as before the function returned only one integer at every call, now it would have to return a rather large array of integers (maybe chars would be enough). zefciu -- http://mail.python.org/mailman/listinfo/python-list
Re: Converting a c array to python list
Dennis Lee Bieber wrote: > Written properly, all it returns is the address of that array data > -- there is no massive copying of data.. I know :) That's why I want to know how to write it properly. zefciu -- http://mail.python.org/mailman/listinfo/python-list
Curious behaviour of Tkinter object
I am writing a program with python and Tkinter. I have encountered a
mysterious problem with the whole application hanging itself (cannot be
stopped with ctrl-c, must be killed from another console). I have done
several tests with interactive mode, and here what I noticed:
- the problem is with a class MandelSetWindow that I attach, as other
classes work properly
- the class can be initialized properly, but behaves strangely with
other windows. Here is how to reproduce this bug:
* import Tkinter.Tk and this class
* create a Tk() instance and take a reference to it
* create an instance to this class (can use (None, None) as arguments)
and take a reference to it
Now everything looks normal. Both references refer to objects like they
were created. But try to e.g. withdraw() either the root Tk window or
this dialog. You will notice that the other withdraws. I really can't
understand why it happens like this.
zefciu
import Tkinter
from mandelpalette import MandelPalette
class MandelSetWindow(Tkinter.Toplevel, object):
"""A dialog window with main fractal settings"""
def __init__(self, settings, callback):
Tkinter.Toplevel.__init__(self)
self.callback = callback
self.textfields = {}
row = 0
for group in [("size", ["width", "height"], "pixel"),
("scale", ["XMin", "XMax", "YMin", "YMax"], ""),
("fractal parameters", ["bailout radius"], "")]:
Tkinter.Label(text = group[0]).grid(row = row, column = 0,
columnspan = 3)
row += 1
for param in group[1]:
Tkinter.Label(text = param).grid(row = row, column = 0)
self.textfields[param] = Tkinter.Entry(width = 10)
self.textfields[param].grid(row = row, column = 1)
Tkinter.Label(text = group[2]).grid(row = row, column = 2)
row += 1
Tkinter.Label(text="palette type").grid(row = row, column = 0)
self.palettebox = Tkinter.Listbox(height = 3)
for paltype in MandelPalette.palette_types:
self.palettebox.insert(Tkinter.END, paltype)
self.palettebox.grid(row = row, column = 1)
row += 1
Tkinter.Label(text="Iteration number").grid(row = row, column = 0)
self.textfields["iterations"] = Tkinter.Entry(width = 10)
self.textfields["iterations"].grid(row = row, column = 1)
row += 1
for butt in [("OK", self.__submit, 0), ("Cancel", self.__cancel, 1),
("Reset", self.__reset, 2)]:
Tkinter.Button(text = butt[0], command = butt[1]).grid(row = row,
column = butt[2])
row += 1
def __getsettings(self):
result = {}
params = ["width", "height", "XMin", "XMax", "YMin", "YMax"]
for i in [("size", 2), ("scale", 4)]:
result[i[0]] = tuple([float(self.textfields[params.pop(0)].\
get()) for j in range(0, i[1])])
result["bailout"] = float(self.textfields["bailout radius"].get())
paltype = self.palettebox.get(self.palettebox.curselection())
iternumber = int(self.textfields["iterations"].get())
result["palette"] = mandelpalette.MandelPalette(iternumber, paltype, 1)
return result
settings = property(__getsettings)
def __submit(self):
self.callback(self.settings)
def __cancel(self):
pass
def __reset(self):
pass
def __fill(self, settings):
pass
class MandelPalette(list):
def __init__(self, size, type, cycles = 1):
try:
self.palette_types[type](self, size, cycles)
except KeyError:
raise ValueError("This palette type is not implemented")
def __genegray(self, size, cycles):
size += 1 # compensating for palette[0]
(levpercycle, remainder) = divmod(size, cycles)
for i in range(0, cycles):
if remainder: # remainder is compensated by first several cycles
remainder -= 1
levpercurrent = levpercycle + 1
else:
levpercurrent = levpercycle
step = 255.0 / (levpercurrent - 1) # if we don't add this -1
# we won't get white
for j in range(0, levpercurrent):
level = int(j * step)
self.append((level, level, level))
def __generain(self, size, cycles):
pass
def __generand(self, size, cycles):
pass
palette_types = {"grayscale" : __genegray,
"rainbow" : __generain,
"random" : __generand}
--
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Re: Hacking in python
enes naci wrote: > > i would like to know about hacking in python too whether its illegal or > not is not the point and anyway it doesn't mean i'm gong to use it. > If you mean hacking as modyfying the code of interpreter of libraries - it is perfectly legal, as Python is Open Source. If you mean hacking as cracking into computer systems, then what's the difference if it's with Python or anything else. If you mean hacking as gaining excellency in programming - then why should it be? Greets zefciu -- http://mail.python.org/mailman/listinfo/python-list
Re: builtin set literal
Paul Rubin wrote:
> There's even a sentiment in some pythonistas to get rid of the [] and {}
> notations for lists and dicts, using list((1,2,3)) and dict((1,2),(3,4))
> for [1,2,3] and {1:2, 3:4} respectively.
Wow. This makes Python twice more LISPy, than <1, 2, 3> and {-} make it
C-ish and Perlish.
Frop Python-zen:
Simple is better than complex.
Flat is better than nested.
Sets are good. Sets are fun. Sets are pythonish (the programmer codes
the logical side of a data structure, bothering less 'bout the
technical). I think, they deserve their literal notation.
zefciu
--
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SystemError: new style getargs format but argument is not a tuple
I am trying to embed a c function in my python script for a first time.
When I try to call it I get an error
SystemError: new style getargs format but argument is not a tuple
Guido said on some mailing list, that it is probably an effect of the
lack of METH_VARARGS in the functions' array, but it's ok in my source
code. Here is the full code:
#include
static PyObject * mandelpixel(PyObject *self, PyObject *args)
{
double z_real = 0, z_imag = 0, z_real2 = 0, z_imag2 = 0, c_real,
c_imag, bailoutsquare;
int iteration_number;
register int i;
PyObject coord;
if (!PyArg_ParseTuple(args, "Oid", &coord, &iteration_number,
&bailoutsquare))
return NULL;
if (!PyArg_ParseTuple(&coord, "dd", &c_real, &c_imag))
return NULL;
for(i = 1; i <= iteration_number; i++)
{
z_imag = 2 * z_real * z_imag + c_imag;
z_real = z_real2 - z_imag2 + c_real;
z_real2 = z_real * z_real;
z_imag2 = z_imag * z_imag;
if (z_real2 + z_imag2 > bailoutsquare)
return Py_BuildValue("i", i);
}
return Py_BuildValue("i", 0);
}
static PyMethodDef MandelcMethods[] =
{
{
"mandelpixel", mandelpixel, METH_VARARGS, "check the pixel for
Mandelbrot set"
},
{
NULL, NULL, 0, NULL
}
};
PyMODINIT_FUNC initmandelc(void)
{
(void) Py_InitModule ("mandelc", MandelcMethods);
}
int main(int argc, char **argv)
{
Py_SetProgramName(argv[0]);
Py_Initialize();
initmandelc();
return 0;
}
Greets
zefciu
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Re: SystemError: new style getargs format but argument is not a tuple
Thinker wrote: > zefciu wrote: >>> I am trying to embed a c function in my python script for a first >>> time. When I try to call it I get an error >>> >>> SystemError: new style getargs format but argument is not a tuple >>> >>> Guido said on some mailing list, that it is probably an effect of >>> the lack of METH_VARARGS in the functions' array, but it's ok in my >>> source code. Here is the full code: > Is coord always tuple? Yes it is. The script launches it with tuple and two numeric arguments. On the other hand when I try it in interactive mode with mandelpixel((1,1), 1, 1) it segfaults, which I completely don't understand. zefciu -- http://mail.python.org/mailman/listinfo/python-list
Re: SystemError: new style getargs format but argument is not a tuple
Thinker wrote: > It should be "PyObject *coord;" . > Maybe, it is what is wrong with your program! > > Should it? The gcc shows me a warning then: warning: 'coord' is used uninitialized in this function and during the execution I get the same error *plus* a segfault. zefciu -- http://mail.python.org/mailman/listinfo/python-list
Re: SystemError: new style getargs format but argument is not a tuple
Thinker wrote: > You can add some printf() to throw out messages to make sure where the > program stop at. > If you can compile the module with debug information and use gdb to > backtrace dump file, > it would be useful. Did it. The arguments are parsed, but the coord tuple isn't. But can PyArg_ParseTuple be used to tuples other than function arguments? If not, what should I use? zefciu -- http://mail.python.org/mailman/listinfo/python-list
Re: SystemError: new style getargs format but argument is not a tuple
Thinker wrote: > Since PyArg_ParseTuple() is supposed to parse arguments, I recommand you > to use PyTuple_GetItem() or PyTuple_GET_ITEM(). Ok. Now I do it this way: c_real = PyFloat_AsDouble(PyTuple_GetItem(coord,0)); c_imag = PyFloat_AsDouble(PyTuple_GetItem(coord,1)); And it worked... once. The problem is really funny - in the interactive the function fails every second time. >>> mandelpixel((1.5, 1.5), 9, 2.2) args parsed coord parsed ii3 >>> mandelpixel((1.5, 1.5), 9, 2.2) TypeError: bad argument type for built-in operation >>> mandelpixel((1.5, 1.5), 9, 2.2) args parsed coord parsed ii3 >>> mandelpixel((1.5, 1.5), 9, 2.2) TypeError: bad argument type for built-in operation etcaetera (the "args parsed" "coord parsed" and "i" are effect of printfs in the code, as you see when it fails, it doesn't even manage to parse the arguments. zefciu -- http://mail.python.org/mailman/listinfo/python-list
Re: SystemError: new style getargs format but argument is not a tuple
Ziga Seilnacht wrote: > The second example uses your approach and is a bit more cumbersome, > but still works. Could you post your current version of the code? > I don't understand where your problem could be. I think, there's no need to. Now I understand :) > if (!PyArg_ParseTuple(args, "Oid", &coord, >&iteration_number, &bailoutsquare)) There was no ampersand in my version before coord. I thought that as coord is already a pointer, PyArg_ParseTuple will want it, not the pointer to the pointer. Now it works, but I will of course change it to get the simpler parenthesised version as in your Example 1. Great thanks :D zefciu -- http://mail.python.org/mailman/listinfo/python-list
Re: Add images together
iceman wrote: > a)Yes, I am using PIL. > b)The color of each pixel over a sequence of frames > If you want to add numerical values of each pixel's colour then itereate through the pixels using nested for loops. But I (and I thing the rest of people here) can't be sure, what in fact you are trying to do. Please provide us with further info - what are you working at? zefciu -- http://mail.python.org/mailman/listinfo/python-list
Re: os.system and quoted strings
svata wrote:
> Hello,
>
> as I'm new to python I've stumbled accros os.system and its not very
> well documented usage.
>
> I use Win XP Pro and Python 2.5.
>
> Here is the code snippet:
>
> --
>
> import time
> import os
>
> dir = "C:\\Documents and Settings\\somepath\\"
> fileName = time.strftime("%d%m%Y")
> os.system('gvim dir+fileName+".txt"')
>
> ---
>
> The problem is that concatenated variable dir+fileName doesn't get
> expanded as expected.
>
> Is there anything I omitted?
>
> svata
>
The way you write it, Python has no idea that dir and fileName are
variables, not literal parts of the string. You should put those names
outside the quotation marks, or better us the % format operator as
Sriram showed
you, or even better use os.path module. Here is the reference:
http://docs.python.org/lib/module-os.path.html
zefciu
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Converting a c array to python list
Hi! I want to embed a function in my python application, that creates a two-dimensional array of integers and passes it as a list (preferably a list of lists, but that is not necessary, as the python function knows the dimensions of this array). As I read the reference, I see, that I must first initialize a list object and then item-by-item put the values to the list. Is there any faster way to do it? And is it worth to implement? The same problem is resolved in the current version by calling a smaller c function (that counts just one element of the array) many times. Will it add much performance to the process? zefciu -- http://mail.python.org/mailman/listinfo/python-list
