pValue is now a PyList - i've even verified this with:
int a = PyList_Check(pValue); printf("%d\n", a);
However, I want to send this PyList to another python module, but I don't know how to do this. Initially I though I could just do like above, only swapping NULL with pValue, but that is not working.
pValue2 is now False! So i guess i cannot pass pValue as an argument to PyObject_CallObject when i want to pass an python list as an argument. But how must a go about to make this work?
Get?? Do you want Set? Is buff a Python function? Or is it the destination of the "sending"? Any good reason for not checking the return value for an error? [Rhetorical question; answer == "No"]
> pValue2 = PyObject_CallObject(pFunc2,pValue);
CallObject?? You used this before because you had a function and wanted to call it because it returned you a value .... now you want to do one of (in Python terms)
value = amodule.anattr value = getattr(amodule, "anattr")
or
amodule.anattr = value setattr(amodule, "anattr", value)
> pValue2 is now False!
False?? Do you mean the C NULL?
> So i guess i cannot pass pValue as an argument > to PyObject_CallObject when i want to pass an python list as an > argument. But how must a go about to make this work?
It's mainly just a matter of (1) knowing what you want to do (2) picking the API that does what you want (3) checking the returned value for error after every call.
> > pValue is now a PyList - i've even verified this with:
> > int a = PyList_Check(pValue); > > printf("%d\n", a);
> > However, I want to send this PyList to another python module,
> Please explain "send" ... do you mean the C equivalent of the Python > statement C_embedding.buff = the_pylist ?
> BTW C-embedding would trigger a syntax error in Python source; best to > avoid ...
I'm sorry I'm not using the proper terms when trying to describe this - i've never really learnt those terms, I guess i should do that one day.
Imagine that the python function C-embedding.buff looks like this:
def buff(a): if isinstance(a,list): print "success"
I want to send, pass, call, whatever a list argument from the C code onto this function. As simple as this - how can you call a function in python from C, and providing a python list as an argument?
As I wrote earlier - I already have a PyList, called pValue. But I have not been able to use this as an argument for C-embedding.buff using the code I described last time.
> Get?? Do you want Set? Is buff a Python function? Or is it the > destination of the "sending"? Any good reason for not checking the > return value for an error? [Rhetorical question; answer == "No"]
> > pValue2 = PyObject_CallObject(pFunc2,pValue);
> CallObject?? You used this before because you had a function and > wanted to call it because it returned you a value .... now you want to > do one of (in Python terms)
> value = amodule.anattr > value = getattr(amodule, "anattr")
> or
> amodule.anattr = value > setattr(amodule, "anattr", value)
> > pValue2 is now False!
> False?? Do you mean the C NULL?
> > So i guess i cannot pass pValue as an argument > > to PyObject_CallObject when i want to pass an python list as an > > argument. But how must a go about to make this work?
> It's mainly just a matter of (1) knowing what you want to do (2) > picking the API that does what you want (3) checking the returned > value for error after every call.
> Imagine that the python function C-embedding.buff looks like this:
> def buff(a): > if isinstance(a,list): > print "success"
> I want to send, pass, call, whatever a list argument from the C code > onto this function. As simple as this - how can you call a function in > python from C, and providing a python list as an argument?
> As I wrote earlier - I already have a PyList, called pValue. But I > have not been able to use this as an argument for C-embedding.buff > using the code I described last time.
> > > but I > > > don't know how to do this. Initially I though I could just do like > > > above, only swapping NULL with pValue, but that is not working.
> > > pName2 = PyString_FromString("C-embedding"); > > > pModule2 = PyImport_Import(pName2); > > > pFunc2 = PyObject_GetAttrString(pModule2,"buff"); > > Any good reason for not checking the > > return value for an error? [Rhetorical question; answer == "No"]
Your problem is here, in the second arg of PyObject_CallObject. It should be either NULL if no args are being supplied, or a tuple containing the args if 1 or more args are being supplied. pValue is the arg itself; you need to wrap it in a tuple.
It contains a very thorough example of calling a Python function from C, with all the reference-counting and error-checking stuff and it's quite runnable -- I've just now compiled it and run it (1) as-is (2) changed to pass a list instead of multiple ints (3) changed again to emulate you trying to pass the list directly instead of wrapped in a tuple ... here's the result:
TypeError: argument list must be a tuple Call failed
Oh by the way, you can get away with C-embedding as a module name if you are importing it from C, but importing it from Python [so that you could test it independently of your C program] presents a difficulty (syntax error) ... better to change it to c_embedding.
> > It's mainly just a matter of (1) knowing what you want to do (2) > > picking the API that does what you want (3) checking the returned > > value for error after every call.
> On Jul 14, 7:22 pm, hartley <hartle...@gmail.com> wrote:> > > I'm very new at wrapping Python/C, and I have run into some problems.
> [snip]
> > > > pValue = PyObject_CallObject(pFunc,NULL);
> > > > pValue is now a PyList - i've even verified this with:
> > > > int a = PyList_Check(pValue); > > > > printf("%d\n", a);
> > > > However, I want to send this PyList to another python module,
> > > Please explain "send" ... do you mean the C equivalent of the Python > > > statement C_embedding.buff = the_pylist ?
> > > BTW C-embedding would trigger a syntax error in Python source; best to > > > avoid ...
> > I'm sorry I'm not using the proper terms when trying to describe this > > - i've never really learnt those terms, I guess i should do that one > > day.
> Today would be a good day to start :-)
> > Imagine that the python function C-embedding.buff looks like this:
> > I want to send, pass, call, whatever a list argument from the C code > > onto this function. As simple as this - how can you call a function in > > python from C, and providing a python list as an argument?
> > As I wrote earlier - I already have a PyList, called pValue. But I > > have not been able to use this as an argument for C-embedding.buff > > using the code I described last time.
> > > > but I > > > > don't know how to do this. Initially I though I could just do like > > > > above, only swapping NULL with pValue, but that is not working.
> > > > pName2 = PyString_FromString("C-embedding"); > > > > pModule2 = PyImport_Import(pName2); > > > > pFunc2 = PyObject_GetAttrString(pModule2,"buff"); > > > Any good reason for not checking the > > > return value for an error? [Rhetorical question; answer == "No"]
> Your problem is here, in the second arg of PyObject_CallObject. It > should be either NULL if no args are being supplied, or a tuple > containing the args if 1 or more args are being supplied. pValue is > the arg itself; you need to wrap it in a tuple.
> It contains a very thorough example of calling a Python function from > C, with all the reference-counting and error-checking stuff and it's > quite runnable -- I've just now compiled it and run it (1) as-is (2) > changed to pass a list instead of multiple ints (3) changed again to > emulate you trying to pass the list directly instead of wrapped in a > tuple ... here's the result:
> TypeError: argument list must be a tuple > Call failed
> Oh by the way, you can get away with C-embedding as a module name if > you are importing it from C, but importing it from Python [so that you > could test it independently of your C program] presents a difficulty > (syntax error) ... better to change it to c_embedding.
> > > It's mainly just a matter of (1) knowing what you want to do (2) > > > picking the API that does what you want (3) checking the returned > > > value for error after every call.
but i still find it hard to read this and find the proper API. The Python/C API reference is 162 pages!
I have a second issue that I've also struggled with, namely using class object (don't shoot me if my terminology is off again). With the little toy class below, i want to instansiate it, boost it, and return it, similar to:
s = ObjectTest() s.boostList() return s.dispList()
printf("Callable\n"); } pObj = PyObject_CallObject(pFunc,NULL); if (pObj != NULL) { printf("WAS NOT NULL!\n");
}
At least this seems to work. However, as to how to actually instantiate and use this class the way I described, I have no idea which API to use. Even though I've spent lots of time reading it! Do you have any clue here, as well?
On Jul 15, 7:54 pm, hartley <hartle...@gmail.com> wrote:
> On Jul 14, 2:21 pm, John Machin <sjmac...@lexicon.net> wrote: > > On Jul 14, 7:22 pm, hartley <hartle...@gmail.com> wrote:> > > I'm very new at wrapping Python/C, and I have run into some problems.
[snip]
/* the first telling */
> > > > statement C_embedding.buff = the_pylist ?
> > > > BTW C-embedding would trigger a syntax error in Python source; best to > > > > avoid ...
/* the second telling */
> > Oh by the way, you can get away with C-embedding as a module name if > > you are importing it from C, but importing it from Python [so that you > > could test it independently of your C program] presents a difficulty > > (syntax error) ... better to change it to c_embedding.
You must have a very strange definition of familiarity! That section has as I pointed out a complete working example of a C program that calls a Python function with 1 or more arguments, complete with error checking and reference counting. To me, familiarity would include reading that program, understanding what it is doing (there are copious explanations), compiling it, running it, then start making changes (like I did) to do things like what you want to do.
> but i still find it hard to read this and find the proper API. The > Python/C API reference is 162 pages!
It's a reference, not a novel. You needed no API that was not in the sample program. What you should do is when you are going through the example programs, look up each API in the reference manual to see what the arguments are supposed to be, what other possibilities there are (e.g. PyObject_CallObject 2nd arg is NULL or a tuple of your args), what the return value is, what if anything is said about reference counts, what similar APIs are there (e.g. a few called PyObject_Callxxxxxxx)
> I have a second issue that I've also struggled with, namely using > class object (don't shoot me if my terminology is off again). With the > little toy class below, i want to instansiate it, boost it, and return > it, similar to:
> s = ObjectTest() > s.boostList() > return s.dispList()
Let's break that down:
alist = s.dispList() return alist
s.dispList (despite its name indicating "display") returns a reference to a list. Your C program is going to return that to whom? The shell?
> but in C, of course.
> so far I have:
> pName = PyString_FromString("ob-test");
/* the third telling */ s/-/_/
"What I tell you three times is true". Just do it.
> pModule = PyImport_Import(pName);
You've imported the module. So far, I'm making the charitable assumption that the lack of error checking is for brevity in your posting, but is there in your actual code.
And if there's a problem, you'll fall through and use the dud reference to the class??
Get into the habit NOW of doing the error checking properly, after each API call; otherwise debugging will become a nightmare. Follow the examples in the sample program. In this case, it is necessary only to test for NULL, and get the correct error message displayed for that. Checking if the returned object is callable in the same if-test clouds the issue. Checking for callability separately is quite unnecessary -- just call the object and you'll find out then if it's not callable.
> pObj = PyObject_CallObject(pFunc,NULL); > if (pObj != NULL) { > printf("WAS NOT NULL!\n");
Again instead of printing congratulatory messages on success, put in proper checking for failure, get the error message printed and bale out.
> }
> At least this seems to work. However, as to how to actually > instantiate and use this class the way I described, I have no idea > which API to use.
You don't know how to instantiate the class? What do you think was the purpose of the PyObject_CallObject() that you just did??
> Even though I've spent lots of time reading it! Do > you have any clue here, as well?
Let's trawl through the Python equivalent of what you want to do:
s = amodule.ObjectTest() (1) import the module (2) get the "objectTest" attribute of the module (3) call it, park the result in s
s.boostList() (1) get the "boostList" attribute of s (2) call it ... but it's a method, maybe we need to use a different PyObject_Callxxxxxx ... no result to park.
x = s.dispList() (1) get the "displist" attribute of s (2) call it (see above), park result in x (3) do something sensible with x
/* the first telling */ (...) /* the second telling */ (...) /* the third telling */
- If you had loosened up on the sarcasm I would probably have read what you wrote more thoroughly instead of just skimming through it. Thanks for the help, but you should seriously consider doing something with your patronizing attitude.
On Jul 16, 11:13 pm, hartley <hartle...@gmail.com> wrote:
> /* the first telling */ > (...) > /* the second telling */ > (...) > /* the third telling */
> - > If you had loosened up on the sarcasm
That wasn't sarcasm, it was an attempt at humourous watering-down the expression of exasperation at continued ignoring of advice and wonder that I was continuing to bother ...
>If you had loosened up on the sarcasm I would probably have read what >you wrote more thoroughly instead of just skimming through it. Thanks >for the help, but you should seriously consider doing something with >your patronizing attitude.
> >If you had loosened up on the sarcasm I would probably have read what > >you wrote more thoroughly instead of just skimming through it. Thanks > >for the help, but you should seriously consider doing something with > >your patronizing attitude.
How To Ask Questions The Smart Way is pretty condescending, especially if you already feel insulted by somebody telling you that you need help asking questions. If you're pointed at a guide with a filename of smart-questions, that means this person thinks you have stupid questions, and who needs that?
>>>If you had loosened up on the sarcasm I would probably have read what >>>you wrote more thoroughly instead of just skimming through it. Thanks >>>for the help, but you should seriously consider doing something with >>>your patronizing attitude.
>How To Ask Questions The Smart Way is pretty condescending, especially >if you already feel insulted by somebody telling you that you need >help asking questions. If you're pointed at a guide with a filename of >smart-questions, that means this person thinks you have stupid >questions, and who needs that?
>Cheers mate :)
Not really. Feel free to chide people trying to help you, eventually people won't care. <shrug> -- Aahz (a...@pythoncraft.com) <*> http://www.pythoncraft.com/
"If you think it's expensive to hire a professional to do the job, wait until you hire an amateur." --Red Adair
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