extracting null pointer address from PyCObject with ctypes

[Gordon Allott]

Hello :)

The result of various incompatibiliti es has left me needing to somehow
extract the address that a null pointer is pointing to with the null
pointer being exposed to python via PyCObject_FromV oidPtr

the code that creates the PyCObject is as follows:
tmp = PyCObject_FromV oidPtr (info.info.x11. display, NULL);
PyDict_SetItemS tring (dict, "display", tmp);
Py_DECREF (tmp);

which is exposed to python via a dictionary (the 'display' key). python
identifies that its a PyCObject but doesn't give any way to expose the
functionality. Essentially I am after the address that the void pointer
'info.info.x11. display' points to (as a long type)

As far as I can tell ctypes will only expose the pyObject type to me and
not actually let me deal with the data I am after, but being rather new
to ctypes I'm not sure weather this is correct.

--
Gord Allott (gordallott@gma il.com)


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[Aaron \Castironpi\ Brady]

Re: extracting null pointer address from PyCObject with ctypes

On Oct 10, 5:24 am, Gordon Allott <gordall...@gma il.comwrote:

Hello :)
>
The result of various incompatibiliti es has left me needing to somehow
extract the address that a null pointer is pointing to with the null
pointer being exposed to python via PyCObject_FromV oidPtr
>
the code that creates the PyCObject is as follows:
    tmp = PyCObject_FromV oidPtr (info.info.x11. display, NULL);
    PyDict_SetItemS tring (dict, "display", tmp);
    Py_DECREF (tmp);
>

Did you try:

tmp= PyLong_FromLong ( ( long ) info.info.x11.d isplay );
PyDict_SetItemS tring (dict, "display", tmp);
Py_DECREF (tmp);

Or also try:

PyCObject_AsVoi dPtr( tmp );

[Gordon Allott]

Re: extracting null pointer address from PyCObject with ctypes

Aaron "Castironpi " Brady wrote:

Did you try:

tmp= PyLong_FromLong ( ( long ) info.info.x11.d isplay );
PyDict_SetItemS tring (dict, "display", tmp);
Py_DECREF (tmp);

Or also try:

PyCObject_AsVoi dPtr( tmp );
--
http://mail.python.org/mailman/listinfo/python-list

the problem is that I can't edit the C code - well I can and might
submit a patch to the project but I also need a solution that works from
the python side of things.


--
Gord Allott (gordallott@gma il.com)


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[Aaron \Castironpi\ Brady]

Re: extracting null pointer address from PyCObject with ctypes

On Oct 10, 12:04 pm, Gordon Allott <gordall...@gma il.comwrote:

Aaron "Castironpi " Brady wrote:

Did you try:

>

tmp= PyLong_FromLong ( ( long ) info.info.x11.d isplay );
PyDict_SetItemS tring (dict, "display", tmp);
Py_DECREF (tmp);

>

Or also try:

>

PyCObject_AsVoi dPtr( tmp );
--
http://mail.python.org/mailman/listinfo/python-list

>
the problem is that I can't edit the C code - well I can and might
submit a patch to the project but I also need a solution that works from
the python side of things.
>

I see. If I understand, you have a PyCObject in a dictionary.

Look at the 'ctypes' module and try calling PyCObject_AsVoi dPtr. Its
return type should be 'c_void_p', and you can use 'result.value' to
get the original pointer.

[Gordon Allott]

Re: extracting null pointer address from PyCObject with ctypes

Aaron "Castironpi " Brady wrote:

I see. If I understand, you have a PyCObject in a dictionary.

Look at the 'ctypes' module and try calling PyCObject_AsVoi dPtr. Its
return type should be 'c_void_p', and you can use 'result.value' to
get the original pointer.
--
http://mail.python.org/mailman/listinfo/python-list

I have a hard time following that, if using ctypes you used PyDLL to
call PyCObject_AsVoi dPtr on the PyCObject I already have surely it would
give me back a pointer (void for sake of simplicity) but it would be a
pointer to a new PyCObject and thus calling result.value on it would
only return the memory address of the new PyCObject?
--
Gord Allott (gordallott@gma il.com)


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[Aaron \Castironpi\ Brady]

Re: extracting null pointer address from PyCObject with ctypes

On Oct 10, 4:16 pm, Gordon Allott <gordall...@gma il.comwrote:

Aaron "Castironpi " Brady wrote:

I see.  If I understand, you have a PyCObject in a dictionary.

>

Look at the 'ctypes' module and try calling PyCObject_AsVoi dPtr.  Its
return type should be 'c_void_p', and you can use 'result.value' to
get the original pointer.
--
http://mail.python.org/mailman/listinfo/python-list

>
I have a hard time following that, if using ctypes you used PyDLL to
call PyCObject_AsVoi dPtr on the PyCObject I already have surely it would
 give me back a pointer (void for sake of simplicity) but it would be a
pointer to a new PyCObject and thus calling result.value on it would
only return the memory address of the new PyCObject?
--
Gord Allott (gordall...@gma il.com)
>
 signature.asc
< 1KViewDownload

Yes, well said. But no, not true, not necessarily. You can choose/
change return types with your code. If the call is defined already
and you can't change the return, just define a new one that returns
long.

[Gordon Allott]

Re: extracting null pointer address from PyCObject with ctypes

Aaron "Castironpi " Brady wrote:

Yes, well said. But no, not true, not necessarily. You can choose/
change return types with your code. If the call is defined already
and you can't change the return, just define a new one that returns
long.
--
http://mail.python.org/mailman/listinfo/python-list

the problem is that the pointer or long or whatever it is thats returned
won't be the data I am after. the code for PyCObject_FromV oidPtr is as
follows:

PyObject *
PyCObject_FromV oidPtr(void *cobj, void (*destr)(void *))
{
PyCObject *self;

self = PyObject_NEW(Py CObject, &PyCObject_Type );
if (self == NULL)
return NULL;
self->cobject=cobj ;
self->destructor=des tr;
self->desc=NULL;

return (PyObject *)self;
}


it obviously creates a new PyObject and returns that, which has already
happened once (the address I am after is passed to python via
PyCObject_FromV oidPtr(adress_i _am_after, NULL), doing that puts the
address I am after into the .cobject attribute of a new pyobject
structure and passes that to the python script via the 'display' key in
a dictionary.

If I were to then take the pycobject in this display key and pass it via
ctypes into PyCObject_FromV oidPtr it would simply create a new pycobject
and put a pointer to the old pycobject in the new pycobject's .cobject
attribute. it just means that I am getting further and further away from
where I want to be surely? if I were to take the current pointer at this
stage, to get to the address I actually want in C it would have to
follow something along the lines of
long address_i_want = (long)(new_pyco bj->cobject->cobject);

What would be great is if there is some easy simple way of accessing the
.cobject attribute of the first pycobject thats passed via the
dictionary to python.

--
Gord Allott (gordallott@gma il.com)


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[Aaron \Castironpi\ Brady]

Re: extracting null pointer address from PyCObject with ctypes

On Oct 10, 7:59 pm, Gordon Allott <gordall...@gma il.comwrote:

Aaron "Castironpi " Brady wrote:

Yes, well said.  But no, not true, not necessarily.  You can choose/
change return types with your code.  If the call is defined already
and you can't change the return, just define a new one that returns
long.
--
http://mail.python.org/mailman/listinfo/python-list

>
the problem is that the pointer or long or whatever it is thats returned
won't be the data I am after. the code for PyCObject_FromV oidPtr is as
follows:
>
PyObject *
PyCObject_FromV oidPtr(void *cobj, void (*destr)(void *))
{
    PyCObject *self;
>
    self = PyObject_NEW(Py CObject, &PyCObject_Type );
    if (self == NULL)
        return NULL;
    self->cobject=cobj ;
    self->destructor=des tr;
    self->desc=NULL;
>
    return (PyObject *)self;
>
}
>
it obviously creates a new PyObject and returns that, which has already
happened once (the address I am after is passed to python via
PyCObject_FromV oidPtr(adress_i _am_after, NULL), doing that puts the
address I am after into the .cobject attribute of a new pyobject
structure and passes that to the python script via the 'display' key in
a dictionary.
>
If I were to then take the pycobject in this display key and pass it via
ctypes into PyCObject_FromV oidPtr it would simply create a new pycobject
 and put a pointer to the old pycobject in the new pycobject's .cobject
attribute. it just means that I am getting further and further away from
where I want to be surely? if I were to take the current pointer at this
stage, to get to the address I actually want in C it would have to
follow something along the lines of
long address_i_want = (long)(new_pyco bj->cobject->cobject);
>
What would be great is if there is some easy simple way of accessing the
.cobject attribute of the first pycobject thats passed via the
dictionary to python.
>
--
Gord Allott (gordall...@gma il.com)
>
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< 1KViewDownload

You are hard to follow. There is the 'cast' function, which I've had
some success with, even in adding pointers and offsets. It took a
look at the code for it though, and calling an undocumented version of
it. I can post that later if you don't have luck the same. You can
write extension modules to do that as well, and there's always a
Google search which personally I forget half the time too. Last, you
haven't mentioned an attempt with PyCObject_AsVoi dPtr yet:

void* PyCObject_AsVoi dPtr(PyObject* self)
Return the object void * that the PyCObject self was created with.

Where does that get you?

[Gordon Allott]

Re: extracting null pointer address from PyCObject with ctypes

Aaron "Castironpi " Brady wrote:

You are hard to follow. There is the 'cast' function, which I've had
some success with, even in adding pointers and offsets. It took a
look at the code for it though, and calling an undocumented version of
it. I can post that later if you don't have luck the same. You can
write extension modules to do that as well, and there's always a
Google search which personally I forget half the time too. Last, you
haven't mentioned an attempt with PyCObject_AsVoi dPtr yet:

void* PyCObject_AsVoi dPtr(PyObject* self)
Return the object void * that the PyCObject self was created with.

Where does that get you?
--
http://mail.python.org/mailman/listinfo/python-list

sorry yes you were right, I was reading PyCObject_AsVoi dPtr as
PyCObject_FromV oidPtr :)

using AsVoidPtr is a little confusing, this is the code I am using:
display = pygame.display. get_wm_info()['display']
pyobj = py_object(displ ay)
ref = pointer(pyobj)

print pythonapi.PyCOb ject_AsVoidPtr( ref)

it produces the following traceback:
Traceback (most recent call last):
File "pygametest.py" , line 125, in <module>
app = PyGameOGREApp()
File "pygametest.py" , line 33, in __init__
self._createWin dow(width, height, fullscreen)
File "pygametest.py" , line 64, in _createWindow
print pythonapi.PyCOb ject_AsVoidPtr( ref)
TypeError: PyCObject_AsVoi dPtr with non-C-object

- I think that's because its a pointer to the ctypes py_object() rather
than the PyCObject we are dealing with but I have no idea how to create
a pointer to that.

--
Gord Allott (gordallott@gma il.com)


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[Aaron \Castironpi\ Brady]

Re: extracting null pointer address from PyCObject with ctypes

On Oct 10, 10:54 pm, Gordon Allott <gordall...@gma il.comwrote:

Aaron "Castironpi " Brady wrote:
snip

 Last, you
haven't mentioned an attempt with PyCObject_AsVoi dPtr yet:

>

void* PyCObject_AsVoi dPtr(PyObject* self)
    Return the object void * that the PyCObject self was created with.

>

Where does that get you?
--
http://mail.python.org/mailman/listinfo/python-list

>
sorry yes you were right, I was reading PyCObject_AsVoi dPtr as
PyCObject_FromV oidPtr :)
>
using AsVoidPtr is a little confusing, this is the code I am using:
        display = pygame.display. get_wm_info()['display']
        pyobj = py_object(displ ay)
        ref = pointer(pyobj)
>
        print pythonapi.PyCOb ject_AsVoidPtr( ref)
>
it produces the following traceback:
Traceback (most recent call last):
  File "pygametest.py" , line 125, in <module>
    app = PyGameOGREApp()
  File "pygametest.py" , line 33, in __init__
    self._createWin dow(width, height, fullscreen)
  File "pygametest.py" , line 64, in _createWindow
    print pythonapi.PyCOb ject_AsVoidPtr( ref)
TypeError: PyCObject_AsVoi dPtr with non-C-object
>
- I think that's because its a pointer to the ctypes py_object() rather
than the PyCObject we are dealing with but I have no idea how to create
a pointer to that.
>

My pygame install just returns an integer in get_wm_info. Take a
look:

>>pygame.displa y.get_wm_info()

{'window': 1180066, 'hglrc': 0}

>>pygame.displa y.get_wm_info()['window']

1180066

>>ctypes.c_void _p( _ )

c_void_p(118006 6)

You're suggesting yours looks like this:

>>pygame.displa y.get_wm_info()

{ ... 'display': ctypes.py_objec t( 1180066 ), ... }

What does type( display ) give you?

[Gordon Allott]

Re: extracting null pointer address from PyCObject with ctypes

Aaron "Castironpi " Brady wrote:

My pygame install just returns an integer in get_wm_info. Take a
look:

>>>pygame.displ ay.get_wm_info( )

{'window': 1180066, 'hglrc': 0}

>>>pygame.displ ay.get_wm_info( )['window']

1180066

>>>ctypes.c_voi d_p( _ )

c_void_p(118006 6)

You're suggesting yours looks like this:

>>>pygame.displ ay.get_wm_info( )

{ ... 'display': ctypes.py_objec t( 1180066 ), ... }

What does type( display ) give you?
--
http://mail.python.org/mailman/listinfo/python-list

yes its different on windows and linux, windows only has a few items
where linux has many more. 'window' is just the window 'id' at any rate
which is not the data I am after (which is internally an address to an
xlib structure)
this is what pygame.display. get_wm_info() returns on linux:
{'fswindow': 31457283, 'wmwindow': 31457284, 'window': 31457294,
'lock_func': <PyCObject object at 0x89dfa70>, 'unlock_func': <PyCObject
object at 0x89dfa88>, 'display': <PyCObject object at 0x89dfa58>}

note how the display object is a PyCObject, thats got the address I want
inside it.


--
Gord Allott (gordallott@gma il.com)


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[Aaron \Castironpi\ Brady]

Re: extracting null pointer address from PyCObject with ctypes

On Oct 11, 9:45 am, Gordon Allott <gordall...@gma il.comwrote:

Aaron "Castironpi " Brady wrote:
>

My pygame install just returns an integer in get_wm_info.  Take a
look:

>

>>pygame.displa y.get_wm_info()

{'window': 1180066, 'hglrc': 0}

>>pygame.displa y.get_wm_info()['window']

1180066

>>ctypes.c_void _p( _ )

c_void_p(118006 6)

>

You're suggesting yours looks like this:

>

>>pygame.displa y.get_wm_info()

{ ... 'display': ctypes.py_objec t( 1180066 ), ... }

>

What does type( display ) give you?
--
http://mail.python.org/mailman/listinfo/python-list

>
yes its different on windows and linux, windows only has a few items
where linux has many more. 'window' is just the window 'id'  at any rate
which is not the data I am after (which is internally an address to an
xlib structure)
this is what pygame.display. get_wm_info() returns on linux:
{'fswindow': 31457283, 'wmwindow': 31457284, 'window': 31457294,
'lock_func': <PyCObject object at 0x89dfa70>, 'unlock_func': <PyCObject
object at 0x89dfa88>, 'display': <PyCObject object at 0x89dfa58>}
>
note how the display object is a PyCObject, thats got the address I want
 inside it.
>

What does print pythonapi.PyCOb ject_AsVoidPtr( display) give you?

[Gordon Allott]

Re: extracting null pointer address from PyCObject with ctypes

Aaron "Castironpi " Brady wrote:

What does print pythonapi.PyCOb ject_AsVoidPtr( display) give you?
--
http://mail.python.org/mailman/listinfo/python-list

Traceback (most recent call last):
File "pygametest.py" , line 125, in <module>
app = PyGameOGREApp()
File "pygametest.py" , line 33, in __init__
self._createWin dow(width, height, fullscreen)
File "pygametest.py" , line 65, in _createWindow
print pythonapi.PyCOb ject_AsVoidPtr( display)
ctypes.Argument Error: argument 1: <type 'exceptions.Typ eError'>: Don't
know how to convert parameter 1


--
Gord Allott (gordallott@gma il.com)


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[Aaron \Castironpi\ Brady]

Re: extracting null pointer address from PyCObject with ctypes

On Oct 11, 1:59 pm, Gordon Allott <gordall...@gma il.comwrote:

Aaron "Castironpi " Brady wrote:
>

What does print pythonapi.PyCOb ject_AsVoidPtr( display) give you?
--
http://mail.python.org/mailman/listinfo/python-list

>
Traceback (most recent call last):
  File "pygametest.py" , line 125, in <module>
    app = PyGameOGREApp()
  File "pygametest.py" , line 33, in __init__
    self._createWin dow(width, height, fullscreen)
  File "pygametest.py" , line 65, in _createWindow
    print pythonapi.PyCOb ject_AsVoidPtr( display)
ctypes.Argument Error: argument 1: <type 'exceptions.Typ eError'>: Don't
know how to convert parameter 1
>
--
Gord Allott (gordall...@gma il.com)
>
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< 1KViewDownload

If anyone knows this better, feel free to step in.

Put this before the call:

ctypes.pythonap i.PyCObject_AsV oidPtr.restype = ctypes.c_void_p
ctypes.pythonap i.PyCObject_AsV oidPtr.argtypes = [ ctypes.py_objec t ]

The reason is that this is the default signature, which is wrong:

>>ctypes.python api.PyCObject_A sVoidPtr.restyp e

<class 'ctypes.c_long' >

>>ctypes.python api.PyCObject_A sVoidPtr.argtyp es
>>>

There are other ways to prototype it if you like, too.

[Gordon Allott]

Re: extracting null pointer address from PyCObject with ctypes

Aaron "Castironpi " Brady wrote:

>>>ctypes.pytho napi.PyCObject_ AsVoidPtr.resty pe

<class 'ctypes.c_long' >

>>>ctypes.pytho napi.PyCObject_ AsVoidPtr.argty pes
>>>>

thank you so much, this works perfectly :)


--
Gord Allott (gordallott@gma il.com)


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