On 13/12/2012 11:36 AM, Dave Calkins wrote:
I'd like to be able to call an OLE Automation (IDispatch) server from
python to automate an existing application. I'm not at liberty to
change the existing automation interface provided by the application so
I need to get it to work with what the app currently exposes.
The interface I'm attempting to work with makes use of "out params".
Here's an excerpt from the IDL for a small sample app I created to
reproduce the issue.
==========
dispinterface IMyApp
{
properties:
methods:
[id(1)] void ShowMessage(BSTR msg);
[id(2)] void SetSettingValue(BSTR settingName, BSTR
settingValue);
[id(3)] void GetSettingValue(BSTR settingName, BSTR*
settingValue);
};
==========
The first two methods are straightforward and I had no problem calling
them from python. The problem is the third one, GetSettingValue, since
it requires you to pass in a reference to a variable which it then fills
in for you.
I read through CH12 of "Python Programming on Win32" by Hammond/Robinson
as a guide. Based on that I installed pywin32 and then tried running
MakePy. Here's an excerpt of the code generated by MakePy.
==========
def GetSettingValue(self, settingName=defaultNamedNotOptArg,
settingValue=defaultNamedNotOptArg):
return self._oleobj_.InvokeTypes(3, LCID, 1, (24, 0), ((8, 0),
(16392, 0)),settingName
, settingValue)
def SetSettingValue(self, settingName=defaultNamedNotOptArg,
settingValue=defaultNamedNotOptArg):
return self._oleobj_.InvokeTypes(2, LCID, 1, (24, 0), ((8, 0),
(8, 0)),settingName
, settingValue)
def ShowMessage(self, msg=defaultNamedNotOptArg):
return self._oleobj_.InvokeTypes(1, LCID, 1, (24, 0), ((8,
0),),msg
)
==========
Comparing what it generated for GetSettingValue vs. SetSettingValue I
noted the difference of 16392 vs. 8. Looking up those in the windows
headers it appears those numeric constants correspond to
VT_BYREF|VT_BSTR vs. VT_BSTR. So MakePy is generating something
different for the "out param" and it seems to even be noticing that its
by reference.
I haven't figured out how to actually call this, though. In CH12 of the
book I mentioned, it is noted that for such methods the params are
converted to return values instead. The example given in the book is:
==========
ok = GetSize( &left, &right, &top, &bottom);
becomes
left, right, top, bottom = GetSize()
==========
It doesn't appear that this is happening with the MakePy results I'm
getting. But clearly MakePy is detecting the "by reference" parameter.
Here's the output I get when attempting to call this method. I just
sort of guessed at how I might call that method.
==========
Python 2.7.3 (default, Apr 10 2012, 23:31:26) [MSC v.1500 32 bit
(Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import win32com.client
>>> x = win32com.client.Dispatch("MyApp.Application")
>>> x.ShowMessage("Hello, world")
>>> x.SetSettingValue("sName","sValue")
>>> sValue = ""
>>> x.GetSettingValue("sName",sValue)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<COMObject MyApp.Application>", line 2, in GetSettingValue
pywintypes.com_error: (-2147352571, 'Type mismatch.', None, 2)
>>> sValue = x.GetSettingName("sName")
This is the form you should use, but the method name you are trying to
call is "GetSettingValue", not "GetSettingName", hence the AttributeError.
Mark
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File
"C:\Users\dave\apps\Python273\lib\site-packages\win32com\client\dynamic.py",
line 522, in __getattr__
raise AttributeError("%s.%s" % (self._username_, attr))
AttributeError: MyApp.Application.GetSettingName
>>>
==========
Any advice on how I can make use of this method, which takes "out
params", from python?
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