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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