Assing a COM Interface to a Python object for callbacks

[Mikko Ohtamaa]

Hi,

I am quite new to Python, PythonCom and COM generally. As a former
Java programmer, I have found Python's flexible ability to access
native Win32, especially COM, very comfortable. However, there is
quite little on-line documentation and examples available about
PythonCOM. The only good sources I have found were the sample chapter
from Mark Hammond's book and some decades old PowerPoint show.

I have a following problem:

I am trying to do XML Schema validation using MSXML SAX parser through
PythonCOM API.

MSXML offers two different interfaces for SAX: One for VB and one for
C++. C++ one is named ISAXXMLReader and VB one is named
IVBSAXXMLReader . I haven't found what is the basic difference between
these interfaces though I have carefully read MSXML SDK documentation.
I assume IVBSAXXMLReader might have some IDispatch functionality which
is requirement for PythonCom(?).

The problem is that SAX Parser requires COM interface for callback.
You must assign a COM interface as a handler to the parser. When the
parsing begins, the handler calls this interface.

saxReader.error Handler = myErrorHandler <-- COM Interface

I do not know how to turn Python class into COM interface on the fly.

I have managed to open the C++ version ISAXXMLReader of the interface.
I have NOT succeed to do this for VB versioon IVBSAXXMLReader , because
I do not know how it happens. I assume you have to use
CoCreateInstanc e, but it returns "Class not registered", see the
sample below.

After opening ISAXXMLReader I have not been able to pass COM error
handler for it. I have reasons not to go through full process
registering my own error handler as a COM server into Windows registry
and create it using win32com.client .Dispatch("Pyth on.MyErrorHandl er").
Is there a way to create COM server on the fly and get the COM handle
for it? I have been trying to read win32.client and win32.server
Python sources and even PythonCOM C sources, but unfortunately my
skillz are not 1337 enough to see the big picture.

How to assign a COM Interface for a Python object? It goes somehow
through policies and wrapping, right? Unfortunately every approach I
have tried end to an error saying my wrapper IPyDispatch cannot be
used as ISAXErrorHandle r.

Mikko Ohtamaa
Student of Industrial Engineering & Management
Oulu, Finland

Sample code:

class MySaxErrorHandl er:

# Some random stuff in stucked into this class
# hoping it would help policies & wrapping
_reg_progid_ = "Art2ComponentV alidator.SaxErr orHandler"
_reg_clsid_ = "{a60511c4-ccf5-479e-98a3-dc8dc545b7d0}"
_reg_clsctx_ = "INPROC_SER VER"
_com_interfaces = [ "{a60511c4-ccf5-479e-98a3-dc8dc545b7d0}" ]
_query_interfac e_ = "{a60511c4-ccf5-479e-98a3-dc8dc545b7d0}"
_public_methods _ = [ "error", "fatalError ", "ignorableWarni ng" ]

# A piece of VB sample:
#Private Sub IVBSAXErrorHand ler_error(ByVal oLocator As
SXML2.IVBSAXLoc ator,

strErrorMessage As String, ByVal nErrorCode As Long)
# WriteErrorToRes ults "Error", strErrorMessage , _
# nErrorCode, oLocator.lineNu mber, oLocator.column Number
#End Sub

def error(oLocator, strErrorMessage , nErrorCode):
print strErrorMessage

def fatalError(oLoc ator, strErrorMessage , nErrorCode):
print strErrorMessage

def ignorableWarnin g(oLocator, strErrorMessage , nErrorCode):
print strErrorMessage

def saxtest():

# SAXXmlReader MIDL: a4f96ed0-f829-476e-81c0-cdc7bd2a0802
# sax error handler: a60511c4-ccf5-479e-98a3-dc8dc545b7d0
# ivbsaxerrorhand ler: d963d3fe-173c-4862-9095-b92f66995f52
# ivbsaxxmlreader : 8c033caa-6cd6-4f73-b728-4531af74945f

# test path switcher
useISAX = 0

if useISAX:
# Use c++ version ISAXXMLReader
saxReader = win32com.client .Dispatch("Msxm l2.SAXXMLReader .4.0")
errorHandler = MySaxErrorHandl er()

# ISAXErrorHandle r: a60511c4-ccf5-479e-98a3-dc8dc545b7d0

iid = pywintypes.IID( "{a60511c4-ccf5-479e-98a3-dc8dc545b7d0}")

# What I should do instead of this?
saxReader.error Handler =
win32com.server .util.wrap(erro rHandler, iid)

# Following error:
# File "C:\Python22\Li b\site-packages\win32c om\server\util. py",
line 28, in wrap
# ob = ob.QueryInterfa ce(iid) # Ask the PyIDispatch
if it supports it?
# pywintypes.com_ error: (-2147467262, 'No such interface
supported', None, None)

else:
# Use VB version, IVBSAXXMLreader
clsid = pywintypes.IID( "{8c033caa-6cd6-4f73-b728-4531af74945f}")
iid = clsid
create_as = win32com.client .pythoncom.CLSC TX_INPROC_SERVE R
iface = win32com.client .pythoncom.CoCr eateInstance(cl sid,
None, create_as, iid)
# pywintypes.com_ error: (-2147221164, 'Class not registered',
None, None)

[Alan Kennedy]

Re: Assing a COM Interface to a Python object for callbacks

Mikko Ohtamaa wrote:
[color=blue]
> I have a following problem:
> I am trying to do XML Schema validation using MSXML SAX parser through
> PythonCOM API.
>
> MSXML offers two different interfaces for SAX: One for VB and one for
> C++. C++ one is named ISAXXMLReader and VB one is named
> IVBSAXXMLReader . I haven't found what is the basic difference between
> these interfaces though I have carefully read MSXML SDK documentation.
> I assume IVBSAXXMLReader might have some IDispatch functionality which
> is requirement for PythonCom(?).
>
> The problem is that SAX Parser requires COM interface for callback.
> You must assign a COM interface as a handler to the parser. When the
> parsing begins, the handler calls this interface.
>
> saxReader.error Handler = myErrorHandler <-- COM Interface
>
> I do not know how to turn Python class into COM interface on the fly.[/color]

I'm not sure how Mark Hammond's Windows extensions handle this
situation, if at all.

But I do know that Thomas Heller's "ctypes" has a COM framework which
addresses the problem. Only thing is, I don't know how robust the
current support is, given that, in Thomas own words: "Warning: work in
progress".

http://starship.python.net/crew/theller/ctypes/sum_sample.html

HTH,

--
alan kennedy
-----------------------------------------------------
check http headers here: http://xhaus.com/headers
email alan: http://xhaus.com/mailto/alan

[Alan Kennedy]

Re: Assing a COM Interface to a Python object for callbacks

Mikko Ohtamaa wrote:
[color=blue]
> I have a following problem:
> I am trying to do XML Schema validation using MSXML SAX parser through
> PythonCOM API.
>
> MSXML offers two different interfaces for SAX: One for VB and one for
> C++. C++ one is named ISAXXMLReader and VB one is named
> IVBSAXXMLReader . I haven't found what is the basic difference between
> these interfaces though I have carefully read MSXML SDK documentation.
> I assume IVBSAXXMLReader might have some IDispatch functionality which
> is requirement for PythonCom(?).
>
> The problem is that SAX Parser requires COM interface for callback.
> You must assign a COM interface as a handler to the parser. When the
> parsing begins, the handler calls this interface.
>
> saxReader.error Handler = myErrorHandler <-- COM Interface
>
> I do not know how to turn Python class into COM interface on the fly.[/color]

I'm not sure how Mark Hammond's Windows extensions handle this
situation, if at all.

But I do know that Thomas Heller's "ctypes" has a COM framework which
addresses the problem. Only thing is, I don't know how robust the
current support is, given that, in Thomas own words: "Warning: work in
progress".

http://starship.python.net/crew/theller/ctypes/sum_sample.html

HTH,

--
alan kennedy
-----------------------------------------------------
check http headers here: http://xhaus.com/headers
email alan: http://xhaus.com/mailto/alan

[John J. Lee]

Re: Assing a COM Interface to a Python object for callbacks

Alan Kennedy <alanmk@hotmail .com> writes:
[color=blue]
> Mikko Ohtamaa wrote:[/color]
[...][color=blue][color=green]
> > The problem is that SAX Parser requires COM interface for callback.
> > You must assign a COM interface as a handler to the parser. When the
> > parsing begins, the handler calls this interface.[/color][/color]
[...]

See Mark Hammond's examples in the win32com/tests directory (IIRC)
that win32all installs in your Python directory. I can't remember
which example demonstrates this, but I'm pretty sure one does.
There's also been some discussion on c.l.py on this.


John