memcpy

[Tim]

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 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

 

[Marc 'BlackJack' Rintsch]

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 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

 

[Tim]

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 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

 

[Laurent Pointal]

Tim a écrit :

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.

 

[Marc 'BlackJack' Rintsch]

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 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

 

[Tim]

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 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]

 

[Marc 'BlackJack' Rintsch]

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