Nevermind, I was able to solve it using _midlSAFEARRAY, and am posting
my solution below in case anyone else is having similar difficulty
(since the mailing lists are indexed by search engines).
import comtypes
import ctypes
class ScanData(ctypes.Structure):
_fields_ = [('mass_width', ctypes.c_double),
('mass', ctypes.c_double),
('charge', ctypes.c_long),
('scan', ctypes.c_long)]
def to_struct(variant, struct):
'''
Convert variant array of structs to tuple of structs.
Args:
variant (VARIANT): filled VARIANT
struct (Structure): struct with _fields_
'''
safe_array = comtypes.safearray._midlSAFEARRAY(struct)
return ctypes.cast(variant._.pparray, safe_array).unpack()
scandata = comtypes.automation.VARIANT()
size = ctypes.c_long()
handle.GetDataFromScan(scandata, size)
items = to_struct(scandata, ScanData)
print(items[0].mass_width)
Thanks for the excellent library,
Alex
On 03/24/2016 10:34 AM, Alex Huszagh wrote:
> Hi,
>
> I'm working with a well-documented, but proprietary DLL I would like to
> call from Python, meaning I have no ability to edit the DLL.
>
> The method documentation itself follows something similar to the
> following:
>
> GetDataFromScan(long nScanNumber,
> LPVARIANT pvarScanData,
> LPLONG pnArraySize)
>
>
> Where pvarScanData is filled with ScanData structs of the similar format:
>
> struct ScanData
> {
> double dMassWidth;
> double dMass;
> long nCharge;
> long nScan;
> };
>
> So far, to try to extract data from the DLL, I have tried using various
> parameters with comtypes.automation.VARIANT, with no success.
>
>
> import comtypes
> import ctypes
>
> CLSID = '{........-....-....-....-............}'
> handle = comtypes.client.CreateObject(CLSID)
>
>
> scandata = comtypes.automation.VARIANT()
> size = ctypes.c_long()
>
> # response is 0 for success, > 0 for error
> response = handle.GetDataFromScan(scandata, size)
>
>
> Now, this works when no data is returned, however, for size > 1, an
> error is returned and no data fills the variant. So I therefore looked
> to initialize the variant. I also tried throwing various parameters,
> such as `comtypes.automation.VARIANT(comtypes.automation.VT_ARRAY)`,
> however, the few I tried (VT_ARRAY, VT_UNKNOWN) all caused the method to
> fail (produce a response > 0) even when no data was returned.
>
> I'm wondering if there's any method to initialize the Variant with a
> method like VariantInit, and then copy the data to a numpy array using
> the comtypes safearray. Any insight would be wonderful.
>
> Thank you,
> Alex
>
--
Alex Huszagh
Lan Huang Laboratory
Department of Physiology and Biophysics
University of California, Irvine
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