Python Programming On Win32

Passing and Obtaining Python Objects from COM

COM supports a variety of argument types, using the VARIANT data structure. The types that can be passed to COM functions include integers and floats of various sizes, strings, date/time values, COM objects, or arrays of any of these types.

In many cases, PythonCOM can translate between Python objects and VARIANT structures seamlessly. When you call a COM object and pass a Python object, PythonCOM automatically creates a VARIANT of the right type and passes the VARIANT to COM. In the absence of any hints, PythonCOM performs the translations as listed in Table 12.1 and Table 12.2. In Table 12.1, for example, you can see that a Python integer is automatically converted to a VARIANT type VT_I4.

Table 12.1. Default Python Object to VARIANT Translation

Python Object Type	VARIANT Type
Integer	VT_I4
Long Integer	VT_I4 if the value is less than 232, or VT_I8 if greater
String/Unicode	VT_BSTR
Float	VT_R8
PyTrue/PyFalse	VT_BOOL
None	VT_NULL
win32com.client.Dispatch instance	VT_DISPATCH
PyIDispatch	VT_DISPATCH
All other PyI* PythonCOM objects	VT_UNKNOWN
Pywintypes PyTIME object	VT_DATE
Any other Python sequence	An array of VARIANTs; each element of the sequence is translated using this table

Table 12.2. Default Python Object to VARIANT Translation

VARIANT Type	Python Object
VT_BOOL VT_I2 VT_I4 VT_ERROR	Integer
VT_R4 VT_R8	Float
VT_DISPATCH	PyIDispatch
VT_UNKNOWN