[Numpy-discussion] NumPy int32 array to Excel through COM server is failing

Raul Cota raul@virtualmaterials....
Sat Jan 26 11:56:34 CST 2013


We came across a problem trying to get an array across COM when wrapped 
as a COM server using the win32com extension.

What caught our attention is that arrays of type float64 work fine but 
do not work for any other array.

Does anyone know if there is something we could do at the NumPy level to 
make it work ?

Arrays are mapped onto Variant/SafeArray and the conversion to a Variant 
seems to be failing for anything that is not a float64.

It is not a huge deal for us to workaround the problem but it is kind of 
ugly and I just wanted to make sure there was not something simple that 
could be done (particularly if something like this would be considered a 

I include working sample code below that reproduces the problem where 
Excel instantiates a com server and requests an array of size and dtype. 
On the Python side, the code sets up the com server and exposes the 
function that just returns an array of ones.

Code in Excel to get an array:
Public Sub NumPyVariantTest()
     Dim npcom As Object
     Dim arr

     '... instantiate com object
     Set npcom = CreateObject("NPTest.COM")
     size = 7

     '... test float64. Works !
     arr = npcom.GetNPArray(size, "float64")

     '... test int32. Fails !
     arr = npcom.GetNPArray(size, "int32")

End Sub

Code in Python to set up com server and expose the GetNPArray function
import win32com.server.util
import win32com.client

import sys, os
import numpy
from numpy import zeros, ones, array

class NPTestCOM(object):
     """COM accessible version of CommandInterface"""

     _reg_clsid_ = "{A0E551F5-2F22-4FB4-B28E-FF1B6809D21C}"
     _reg_desc_  = "NumPy COM Test"
     _reg_progid_ = "NPTest.COM"
     _reg_clsctx_ = CLSCTX_INPROC
     _public_methods_ = ['GetNPArray']

     _public_attrs_ = []
     _readonly_attrs_ = []

     def GetNPArray(self, size, dtype):
         """ Return an arbitrary NumPy array of type dtype to check
         conversion to Variant"""
         return ones(size, dtype=dtype)

if __name__ == '__main__':
     import win32com.server.register
     import _winreg

     dllkey = 'nptestdll'

     if len(sys.argv) > 1 and sys.argv[1] == 'unregister':
         software_key = _winreg.OpenKey(_winreg.HKEY_LOCAL_MACHINE, 
         vmg_key = _winreg.OpenKey(software_key, 'VMG')
         _winreg.DeleteKey(vmg_key, dllkey)
         software_key = _winreg.OpenKey(_winreg.HKEY_LOCAL_MACHINE, 
         vmg_key = _winreg.CreateKey(software_key, 'VMG')
         _winreg.SetValue(vmg_key, dllkey, _winreg.REG_SZ, 



Raul Cota (P.Eng., Ph.D. Chemical Engineering)
Research & Development Manager
Phone: (403) 457 4598
Fax:   (403) 457 4637
Virtual Materials Group - Canada

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