[pywin32-bugs] [ pywin32-Bugs-2016768 ] issues with 1-based indexed collections

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Bugs item #2016768, was opened at 2008-07-13 04:54
Message generated for change (Comment added) made by mhammond
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Category: com
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Mark Hammond (mhammond)
Assigned to: Nobody/Anonymous (nobody)
Summary: issues with 1-based indexed collections

Initial Comment:
A report from a thread entitled "[python-win32] problem with win32com and one-based indexed collections" in July 2007.  Full details in next comment.

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>Comment By: Mark Hammond (mhammond)
Date: 2008-07-13 04:55

Message:
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>From initial bug report on the python-win32 mailing list:

I have run across what I believe may be a shortcoming with win32com when
trying to call functions that expect one-based indexed arrays as input. 
The function I'm trying to invoke which demonstrates the problem is defined
in my documentation as follows: 

HRESULT SyncRead(
      [in] SHORT Source,
      [in] LONG NumItems, 
      [in] SAFEARRAY(LONG) * ServerHandles,
      [out] SAFEARRAY(VARIANT) * Values,
      [out] SAFEARRAY(LONG) * Errors,
      [out,optional] VARIANT * Qualities,
      [out,optional] VARIANT * TimeStamps);

In Python, this looks like:

server_handles = [16384,16385] 
num_items = 2
values, errors, qualities, timestamps = groups.SyncRead(2, num_items,
server_handles)

The num_items parameter is supposed to tell the function the total number
sever_handles being passed in.  Anyway, the above code always throws a com
exception and fails.  I am assuming this issue is due to the SyncRead
function using one-based indexing for its array collection. 

However, if I append an extra "dummy" argument to the beginning of the
server_handles list, it will always work.

server_handles = [0, 16384,16385]
num_items = 2
values, errors, qualities, timestamps = groups.SyncRead(2, num_items,
server_handles)

The above example is a very poor solution since it appears to produce a
slow memory leak in my application.  Every 10 to 12 times the SyncRead call
is invoked using the exact same server_handles, memory consumption
increases by 4kb.  This memory leak problem does not happen when called
from VB. 

As an amusing test, I tried setting the variables passed to the function
as follows:

server_handles = [0, 16384, 16385, 0, 0, 0, 0, 0, 0, 0, 0, 0]
num_items = 2

This makes an even bigger memory leak, leading me to believe any extra
elements passed in the list beyond the num_items passed will always be
allocated but never freed. 

Does Mark or anyone else know how to correctly pass a collection to a COM
call using one-based indexing that won't cause a mem leak?   I couldn't
find any mention of this issue in the Python Win32 book other than an Excel
example which didn't seem to apply. 

-BB


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