how to convert pymedia.audio.acodec ACString to ctypes.c_char_p
Hello All Experts,
I am quite new to Ctypes. I am using one c library and writing python
bindings for it.
I need to pass a character pointer to one function.
I am reading one mp3 file and decoding it to raw pcm using pymedia.
Now I need to pass this raw data in to a
C function. Here is my code.
# /*
from ctypes import *
import pymedia.audio.acodec as codec
dec = None
dm = muxer.Demuxer('mp3')
fp = open('test.mp3', 'rb')
fingerprinting_done = False
while not fingerprinting_done:
s = fp.read(2)
frames = dm.parse(s)
for fr in frames:
if dec == None:
dec = codec.Decoder(dm.streams[0])
r = dec.Decode(fr[1])
if r and r.data:
# pass this r.data to the C function.
# r.data is ACString object
# I cannot do pcm_audio = c_char_p(r.data) . gives me
following error
# TypeError: string or integer address expected instead
of ACString instance
# */
I am getting error while converting r.data (which is ACstring object)
in to ctypes.c_char_p.
can you help me solving this problem?
any help would be appericiated,
Thank you,
sanket
--
http://mail.python.org/mailman/listinfo/python-list
segmentation fault while using ctypes
Hello All,
I am dealing with this weird bug.
I have a function in C and I have written python bindings for it using
ctypes.
I can call this function for couple of times and then suddenly it
gives me seg fault.
But I can call same function from a C code for any number of times.
I cannot get what's going on.
here is my code.
/**/
/* C Function I am calling */
int get_hash(char *filename,int rate,int ch,unsigned char* hash,
unsigned int* hash_size,short* avg_f,short* avg_d){
/* some variable declarations here */
fp = fopen(filename,"rb");
data = (signed short *)malloc(sizeof(signed short) * N_BLOCKS);
whereami = WAVE_HEADER_SIZE;
while((!feof(fp)) && (fp_more == 1) && !ferror(fp)){
fp_data_size = fread(data,sizeof(signed short),N_BLOCKS,fp);
whereami += fp_data_size;
fp_more = fp_feed_short(fooid,data,fp_data_size); // call to some
library funtion
} //end while
/* some arithmetic calculations here */
n = my_fp_calculate(fooid,audio_length,fp_fingerprint,&fit,&dom);
if (data != NULL)
free(data)
fclose(fp)
return n;
}
/* END OF C FUNCTION
*/
Python code
-
from ctypes import *
lib = cdll.LoadLibrary("/usr/lib/libclient.so")
def my_func(filename,rate,ch):
hash = (c_ubyte * 424)()
hash_size = c_uint()
avg_f = c_short(0)
avg_d = c_short(0)
n = lib.get_hash(filename,rate,ch,hash,byref(hash_size),byref
(avg_f),byref(avg_d))
hash = None
def main():
for filename in os.listdir(MY_DIR):
print filename
my_func(filename,100,10)
print
""
if __name__ == "__main__":
main()
== END OF PYTHON CODE ==
Thank you in advance,
sanket
--
http://mail.python.org/mailman/listinfo/python-list
Re: segmentation fault while using ctypes
On Apr 14, 4:00 pm, MRAB wrote:
> sanket wrote:
> > Hello All,
>
> > I am dealing with this weird bug.
> > I have a function in C and I have written python bindings for it using
> > ctypes.
>
> > I can call this function for couple of times and then suddenly it
> > gives me seg fault.
> > But I can call same function from a C code for any number of times.
>
> > I cannot get what's going on.
>
> > here is my code.
>
> > /**/
> > /* C Function I am calling */
> > int get_hash(char *filename,int rate,int ch,unsigned char* hash,
> > unsigned int* hash_size,short* avg_f,short* avg_d){
>
> > /* some variable declarations here */
> > fp = fopen(filename,"rb");
>
> You should check the value of 'fp' here.
>
> > data = (signed short *)malloc(sizeof(signed short) * N_BLOCKS);
>
> You should check the value of 'data' here.
>
> > whereami = WAVE_HEADER_SIZE;
>
> What is 'whereami'?
>
> > while((!feof(fp)) && (fp_more == 1) && !ferror(fp)){
> > fp_data_size = fread(data,sizeof(signed short),N_BLOCKS,fp);
>
> 'fp_data_size' will be the number of signed shorts read, not the number
> of bytes. Is this OK?
>
> > whereami += fp_data_size;
>
> The final value of 'whereami' will be WAVE_HEADER_SIZE + the total
> number of signed shorts read.
>
> > fp_more = fp_feed_short(fooid,data,fp_data_size); // call to some
> > library funtion
> > } //end while
>
> > /* some arithmetic calculations here */
>
> > n = my_fp_calculate(fooid,audio_length,fp_fingerprint,&fit,&dom);
>
> > if (data != NULL)
> > free(data)
>
> I don't that 'free()' will complain if 'data' happens to be NULL,
> although you should've already checked whether 'data' is NULL when you
> malloc'ed! :-)
>
> > fclose(fp)
> > return n;
> > }
>
> > /* END OF C FUNCTION
> > */
> >
> > Python code
> > -
> > from ctypes import *
> > lib = cdll.LoadLibrary("/usr/lib/libclient.so")
>
> > def my_func(filename,rate,ch):
> > hash = (c_ubyte * 424)()
> > hash_size = c_uint()
> > avg_f = c_short(0)
> > avg_d = c_short(0)
> > n = lib.get_hash(filename,rate,ch,hash,byref(hash_size),byref
> > (avg_f),byref(avg_d))
> > hash = None
>
> > def main():
> > for filename in os.listdir(MY_DIR):
> > print filename
> > my_func(filename,100,10)
> > print
> > ""
>
> > if __name__ == "__main__":
> > main()
>
> > == END OF PYTHON CODE ==
>
> > Thank you in advance,
> > sanket
> > --
> >http://mail.python.org/mailman/listinfo/python-list
>
>
Thank you for your reply.
I will make check for fp and data pointers.
But my point is this function runs fine while calling it from a C
code.
it only breaks while calling from python. So I wonder if there can be
anything wrong with ctypes module.
Thanks,
sanket
--
http://mail.python.org/mailman/listinfo/python-list
Re: segmentation fault while using ctypes
On Apr 14, 3:56 pm, "Diez B. Roggisch" wrote: > sanket schrieb: > > > Hello All, > > > I am dealing with this weird bug. > > I have a function in C and I have written python bindings for it using > > ctypes. > > > I can call this function for couple of times and then suddenly it > > gives me seg fault. > > But I can call same function from a C code for any number of times. > > > I cannot get what's going on. > > Try debugging it. While a python debug-build might help, I have been > getting good results with a simple > > # gdb python > $ set args testscript.py > $ run > > then when the segfaults hit, get a backtrace. You can also of course set > a berakpoint to the function in question. > > Diez Thanks Diez, I used the gdb but it just crashed and kicked my out of gdb prompt. how can I get a stack trace? Thanks, sanket -- http://mail.python.org/mailman/listinfo/python-list
Re: segmentation fault while using ctypes
On Apr 14, 9:00 pm, bieff...@gmail.com wrote:
> On Apr 15, 12:39 am, sanket wrote:
>
>
>
> > Hello All,
>
> > I am dealing with this weird bug.
> > I have a function in C and I have written python bindings for it using
> > ctypes.
>
> > I can call this function for couple of times and then suddenly it
> > gives me seg fault.
> > But I can call same function from a C code for any number of times.
>
> > I cannot get what's going on.
>
> > here is my code.
>
> > /**/
> > /* C Function I am calling */
> > int get_hash(char *filename,int rate,int ch,unsigned char* hash,
> > unsigned int* hash_size,short* avg_f,short* avg_d){
>
> > /* some variable declarations here */
> > fp = fopen(filename,"rb");
>
> > data = (signed short *)malloc(sizeof(signed short) * N_BLOCKS);
>
> > whereami = WAVE_HEADER_SIZE;
> > while((!feof(fp)) && (fp_more == 1) && !ferror(fp)){
> > fp_data_size = fread(data,sizeof(signed short),N_BLOCKS,fp);
> > whereami += fp_data_size;
> > fp_more = fp_feed_short(fooid,data,fp_data_size); // call to some
> > library funtion
> > } //end while
>
> > /* some arithmetic calculations here */
>
> > n = my_fp_calculate(fooid,audio_length,fp_fingerprint,&fit,&dom);
>
> > if (data != NULL)
> > free(data)
> > fclose(fp)
> > return n;
>
> > }
>
> > /* END OF C FUNCTION
> > */
> >
> > Python code
> > -
> > from ctypes import *
> > lib = cdll.LoadLibrary("/usr/lib/libclient.so")
>
> > def my_func(filename,rate,ch):
> > hash = (c_ubyte * 424)()
> > hash_size = c_uint()
> > avg_f = c_short(0)
> > avg_d = c_short(0)
> > n = lib.get_hash(filename,rate,ch,hash,byref(hash_size),byref
> > (avg_f),byref(avg_d))
> > hash = None
>
> > def main():
> > for filename in os.listdir(MY_DIR):
> > print filename
> > my_func(filename,100,10)
> > print
> > ""
>
> > if __name__ == "__main__":
> > main()
>
> > == END OF PYTHON CODE ==
>
> > Thank you in advance,
> > sanket
>
> You don't show how the C function make use of parameters hash,
> hash_size, avg_f, avg_d. Since you pass them by address,
> I guess that are output parameters, but how do they get written? In
> particular,make sure you don't write into hash more
> than the 424 bytes you allocated for it in the calling python
> code ...
>
> Ciao
>
> FB
Yes, I am making sure that hash wouldn't be written more that 424
bytes in to it.
This is something really weird. I can call this function from C as
many times as I want but not from python
I tracked down the problem and came to know that call to
my_fp_calculate causes the seg fault.
I will debug it and let you guys know.
Thank you all so much for the help. I appreciate it.
sanket
--
http://mail.python.org/mailman/listinfo/python-list
SimpleJson is slow .... is there any C Compiled version ?
Hello All, I have created an API which fetches some data from the database. I am using simplejson to encode it and return it back. Now the problem is that, this API is being called for millions of times in a sequence. I ran a profiler and saw that most of the time is consumed in encoding my database results in to json. So I was just wondering is there any C compiled version of simplejson is available? or any help regarding this issue would be appreciated. Thank you, Sanket -- http://mail.python.org/mailman/listinfo/python-list
Re: SimpleJson is slow .... is there any C Compiled version ?
On Jul 25, 5:52 pm, Matt Nordhoff <[EMAIL PROTECTED]> wrote: > sanket wrote: > > Hello All, > > > I have created an API which fetches some data from the database. > > I am using simplejson to encode it and return it back. > > > Now the problem is that, this API is being called for millions of > > times in a sequence. > > I ran a profiler and saw that most of the time is consumed in encoding > > my database results in to json. > > So I was just wondering is there any C compiled version of simplejson > > is available? > > or any help regarding this issue would be appreciated. > > > Thank you, > > Sanket > > simplejson is not the only JSON library out there. For example, there's > python-cjson, which is written entirely in C: > > <http://pypi.python.org/pypi/python-cjson> > > There's also an enhanced version of it: > > <http://python.cx.hu/python-cjson/> > > I think simplejson has some small, optional C bits that will improve > performance if you compile them. > > Also, be aware that I think simplejson is being integrated into the > stdlib in Python 2.6. > > Also, simplejson and python-cjson might not be entirely compatible: > there's one character that one escapes and the other doesn't, or something. > -- Thanks Matt. I used cjson and it appears to be 5-6 times faster. Thank you, Sanket -- http://mail.python.org/mailman/listinfo/python-list
how to spawn a process under different user
Hello All, I am trying to use python's subprocess module to launch a process. but in order to do that I have to change the user. I am not getting any clue how to do that? so can anyone please tell me How can I spawn a process under different user than currently I am logging in as. Thank you, sanket -- http://mail.python.org/mailman/listinfo/python-list
Re: how to spawn a process under different user
On Jul 2, 1:58 pm, Tim Golden wrote: > sanket wrote: > > Hello All, > > > I am trying to use python's subprocess module to launch a process. > > but in order to do that I have to change the user. > > > I am not getting any clue how to do that? > > so can anyone please tell me How can I spawn a process under different > > user than currently I am logging in as. > > What platform are you on? If you are on Windows, > there was a thread on this subject some time in > the last month. (Short answer: switching user before > launching subprocess won't work; switching within > the subprocess will...) > > TJG Hi TJG, Thanks for the reply. I am using python 2.4 on centos. Thanks, sanket -- http://mail.python.org/mailman/listinfo/python-list
