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Tim
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      09-10-2007
How do I memcpy from a pointer to an array of floats in python?

I get errors: NameError: global name 'row' is not defined

I want to be able to get the row[i] array element. In C I would
normally place the address of row as the first argument.

cdll.msvcrt.memcpy( row, pData, 256 )


If I define row as the following I also get the following error:

row = ones( TOTAL_PARAMETER_ENTRIES, dtype=float )

ArgumentError: argument 1: <type 'exceptions.TypeError'>: Don't know
how to convert parameter 1

Thanks

 
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Marc 'BlackJack' Rintsch
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      09-10-2007
On Mon, 10 Sep 2007 11:38:50 -0700, Tim wrote:

> How do I memcpy from a pointer to an array of floats in python?
>
> I get errors: NameError: global name 'row' is not defined


Well than the (global) name `row` is not defined. Quite clear message,
isn't it?

> I want to be able to get the row[i] array element. In C I would
> normally place the address of row as the first argument.
>
> cdll.msvcrt.memcpy( row, pData, 256 )
>
>
> If I define row as the following I also get the following error:
>
> row = ones( TOTAL_PARAMETER_ENTRIES, dtype=float )
>
> ArgumentError: argument 1: <type 'exceptions.TypeError'>: Don't know
> how to convert parameter 1


You don't give enough information so we have to guess. For example I
guess the `ones()` function comes from one of the packages `numeric`,
`numarray` or `numpy`!?

This function returns a Python object. You can't use arbitrary Python
objects with `ctypes`. `memcpy` expects a pointer not an object.

Ciao,
Marc 'BlackJack' Rintsch
 
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Tim
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      09-11-2007
On Sep 10, 3:31 pm, Marc 'BlackJack' Rintsch <(E-Mail Removed)> wrote:
> On Mon, 10 Sep 2007 11:38:50 -0700, Tim wrote:
> > How do I memcpy from a pointer to an array of floats in python?

>
> > I get errors: NameError: global name 'row' is not defined

>
> Well than the (global) name `row` is not defined. Quite clear message,
> isn't it?
>
> > I want to be able to get the row[i] array element. In C I would
> > normally place the address of row as the first argument.

>
> > cdll.msvcrt.memcpy( row, pData, 256 )

>
> > If I define row as the following I also get the following error:

>
> > row = ones( TOTAL_PARAMETER_ENTRIES, dtype=float )

>
> > ArgumentError: argument 1: <type 'exceptions.TypeError'>: Don't know
> > how to convert parameter 1

>
> You don't give enough information so we have to guess. For example I
> guess the `ones()` function comes from one of the packages `numeric`,
> `numarray` or `numpy`!?
>
> This function returns a Python object. You can't use arbitrary Python
> objects with `ctypes`. `memcpy` expects a pointer not an object.
>
> Ciao,
> Marc 'BlackJack' Rintsch


Can I initialize something in Python that I can get access to it's
pointer?
How about:

self.data =
TOTAL_OUTPUT_PARMETERS*[TOTAL_PARAMETER_ENTRIES*[c_float()]

or

self.data = TOTAL_OUTPUT_PARMETERS*[c_char_p("temp")]

or

self.data = [TOTAL_OUTPUT_PARMETERS*1.0]*TOTAL_PARAMETER_ENTRIES

I need to be able to copy the contents of a pointer to shared memory
into an array of floats so I can index into that array and see my
data. I have a pointer to shared meory but I don't know how to access
it.

Here is what I would like to write:

shared_memory_pointer = windll.kernel32.MapViewOfFile(hMapObject,
FILE_MAP_ALL_ACCESS,
0, 0, TABLE_SHMEMSIZE)

memcpy( self.data, shared_memory_pointer, my_size )

Thanks

 
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Laurent Pointal
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      09-11-2007
Tim a écrit :
<zip>
> Can I initialize something in Python that I can get access to it's
> pointer?


No, there is no pointer in Python semantic (they exist behind the scene
in C-Python).

> How about:
>
> self.data =
> TOTAL_OUTPUT_PARMETERS*[TOTAL_PARAMETER_ENTRIES*[c_float()]
>
> or
>
> self.data = TOTAL_OUTPUT_PARMETERS*[c_char_p("temp")]
>
> or
>
> self.data = [TOTAL_OUTPUT_PARMETERS*1.0]*TOTAL_PARAMETER_ENTRIES
>
> I need to be able to copy the contents of a pointer to shared memory
> into an array of floats so I can index into that array and see my
> data. I have a pointer to shared meory but I don't know how to access
> it.


See module ctypes (14.14 in library reference manual).

A+

Laurent.
 
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Marc 'BlackJack' Rintsch
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      09-11-2007
On Tue, 11 Sep 2007 05:09:58 -0700, Tim wrote:

> On Sep 10, 3:31 pm, Marc 'BlackJack' Rintsch <(E-Mail Removed)> wrote:
>> On Mon, 10 Sep 2007 11:38:50 -0700, Tim wrote:
>> > How do I memcpy from a pointer to an array of floats in python?

>>
>> > I get errors: NameError: global name 'row' is not defined

>>
>> Well than the (global) name `row` is not defined. Quite clear message,
>> isn't it?
>>
>> > I want to be able to get the row[i] array element. In C I would
>> > normally place the address of row as the first argument.

>>
>> > cdll.msvcrt.memcpy( row, pData, 256 )

>>
>> > If I define row as the following I also get the following error:

>>
>> > row = ones( TOTAL_PARAMETER_ENTRIES, dtype=float )

>>
>> > ArgumentError: argument 1: <type 'exceptions.TypeError'>: Don't know
>> > how to convert parameter 1

>>
>> You don't give enough information so we have to guess. For example I
>> guess the `ones()` function comes from one of the packages `numeric`,
>> `numarray` or `numpy`!?
>>
>> This function returns a Python object. You can't use arbitrary Python
>> objects with `ctypes`. `memcpy` expects a pointer not an object.

>
> Can I initialize something in Python that I can get access to it's
> pointer?


"It's pointer"? Then you have a pointer to a structure that represents
the Python object but still no idea what data is at that pointer. This is
an implementation detail of the Python version and of the particular
object.

> Here is what I would like to write:
>
> shared_memory_pointer = windll.kernel32.MapViewOfFile(hMapObject,
> FILE_MAP_ALL_ACCESS,
> 0, 0, TABLE_SHMEMSIZE)
>
> memcpy( self.data, shared_memory_pointer, my_size )


I haven't tested but it should be possible to declare the return type of
`windll.kernel32.MapViewOfFile()` as ``ctypes.POINTER(ctypes.c_double *
256)`` and then do:

test_data = numpy.ones(1000)
shared_memory_pointer.contents[0:256] = test_data[0:256]

Ciao,
Marc 'BlackJack' Rintsch
 
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Tim
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Posts: n/a
 
      09-11-2007
On Sep 11, 8:01 am, Marc 'BlackJack' Rintsch <(E-Mail Removed)> wrote:
> On Tue, 11 Sep 2007 05:09:58 -0700, Tim wrote:
> > On Sep 10, 3:31 pm, Marc 'BlackJack' Rintsch <(E-Mail Removed)> wrote:
> >> On Mon, 10 Sep 2007 11:38:50 -0700, Tim wrote:
> >> > How do I memcpy from a pointer to an array of floats in python?

>
> >> > I get errors: NameError: global name 'row' is not defined

>
> >> Well than the (global) name `row` is not defined. Quite clear message,
> >> isn't it?

>
> >> > I want to be able to get the row[i] array element. In C I would
> >> > normally place the address of row as the first argument.

>
> >> > cdll.msvcrt.memcpy( row, pData, 256 )

>
> >> > If I define row as the following I also get the following error:

>
> >> > row = ones( TOTAL_PARAMETER_ENTRIES, dtype=float )

>
> >> > ArgumentError: argument 1: <type 'exceptions.TypeError'>: Don't know
> >> > how to convert parameter 1

>
> >> You don't give enough information so we have to guess. For example I
> >> guess the `ones()` function comes from one of the packages `numeric`,
> >> `numarray` or `numpy`!?

>
> >> This function returns a Python object. You can't use arbitrary Python
> >> objects with `ctypes`. `memcpy` expects a pointer not an object.

>
> > Can I initialize something in Python that I can get access to it's
> > pointer?

>
> "It's pointer"? Then you have a pointer to a structure that represents
> the Python object but still no idea what data is at that pointer. This is
> an implementation detail of the Python version and of the particular
> object.
>
> > Here is what I would like to write:

>
> > shared_memory_pointer = windll.kernel32.MapViewOfFile(hMapObject,
> > FILE_MAP_ALL_ACCESS,
> > 0, 0, TABLE_SHMEMSIZE)

>
> > memcpy( self.data, shared_memory_pointer, my_size )

>
> I haven't tested but it should be possible to declare the return type of
> `windll.kernel32.MapViewOfFile()` as ``ctypes.POINTER(ctypes.c_double *
> 256)`` and then do:
>
> test_data = numpy.ones(1000)
> shared_memory_pointer.contents[0:256] = test_data[0:256]
>
> Ciao,
> Marc 'BlackJack' Rintsch- Hide quoted text -
>
> - Show quoted text -


Is this what you mean? Python did not like the word c_types in front
of POINTER. Do you know why? How can I re-declare a function's return
type if it is declared somewhere else?

test_data = numpy.ones(1000)
shared_memory_pointer = POINTER(c_float*256)
shared_memory_pointer =
windll.kernel32.MapViewOfFile(hMapObject, FILE_MAP_ALL_ACCESS,
0, 0, TABLE_SHMEMSIZE)
test_data[0:256]= shared_memory_pointer.contents[0:256]

print 'data:', test_data[0]




 
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Marc 'BlackJack' Rintsch
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Posts: n/a
 
      09-11-2007
On Tue, 11 Sep 2007 06:22:19 -0700, Tim wrote:

> Is this what you mean? Python did not like the word c_types in front
> of POINTER. Do you know why?


Yes I know. Read up how importing works.

> How can I re-declare a function's return type if it is declared
> somewhere else?


The return type of C functions wrapped by `ctypes` is always `int` until
you say otherwise. How to do that is covered in the `ctypes`
tutorial/dicumentation.

> test_data = numpy.ones(1000)
> shared_memory_pointer = POINTER(c_float*256)


This binds the resulting "pointer" object to the name
`shared_memory_pointer`.

> shared_memory_pointer =
> windll.kernel32.MapViewOfFile(hMapObject, FILE_MAP_ALL_ACCESS,
> 0, 0, TABLE_SHMEMSIZE)


And here you bind a different object to that name, so the first binding
has no effect.

Ciao,
Marc 'BlackJack' Rintsch
 
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