COM / Variants / VT_BOOL

Mark Hammond MarkH at
Thu Dec 28 07:23:14 EST 2000

Alex Martelli wrote:

> *Almost* right... but not *quite*, and we hit this specific problem
> quite recently (we weren't driving with Python, but I think that
> would have made no difference).

Quite possibly it would.  If win32com had type information, it would 
have dont the right thing.

> Setting the property .ValidateOnParse of the Xerces XML parser
> (originally from IBM, now, I believe, from Apache), in its COM
> setting, to 0 *or* 1, still keeps the parser non-validating; you

Without type info, the parser should call VariantChangeType() to get a 
valid VT_BOOL back.  So really the parser is at fault (or the client for 
ignoring it)

> *Most* COM servers will happily accept 'server.BoolProp = 1'
> as setting the property to 'true', but, I suggest, don't count
> on that; use 'server.BoolProp = -1' and you might be safer.

Also, a feature of the pythoncom type conversion means that you can say:

true = 1==1
false = 1==0

And passing these variables (or the expression as a literal) _will_ 
force a VT_BOOL of the correct type.


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