ctypes FAQ - frequently asked questions

overview :: tutorial :: reference :: faq

( Work in progress: COM :: COM sample )

Windows topics

How do I pass a win32all PyHandle to a dll function?

win32all functions often return a PyHandle object, for example the CreateFile function. ctypes has it's own protocol to convert Python objects into C parameters when it calls functions loaded from a dll, so it does not know how to pass the PyHandle object to the C function.

PyHandle objects have a .handle attribute which is an integer, and this can be passed to a function by ctypes :

           h = win32file.CreateFile(....)
           windll.kernel32.DeviceIoControl(h.handle, ...)

Another possibility is to convert the PyHandle object into an integer by writing the call in this way:

           h = win32file.CreateFile(....)
           windll.kernel32.DeviceIoControl(int(h), ...)

How can I call functions in a dll written in Delphi?

Delphi uses the PASCAL calling convention as default, and this expects the parameters in reverse order. Write the arguments in reverse order in the call, and it should work when using the __stdcall calling convention (load the Delphi dll with windll).

General topics

How can I access a value (an integer, a pointer) in a shared library?

New in 0.6.1: ctypes types now have a .in_dll class method, which accepts a dll/shared library instance and a symbol name as parameters. See the tutorial for details.

How can I load a dll named gpib-32.dll?

ctypes loads dlls by retrieving them as attributes from windll or cdll, like windll.gdi32 which loads gdi32.dll. This approach cannot work when the filename contains characters not allowed in Python identifiers, or when the dll is not on the default Windows search path. In these cases you should call the CDLL or WinDLL classes directly with the filename:

           gpib32 = CDLL("c:\\gpib\\gpib-32.dll")

How can I call functions written in "C++" ?

Jimmy Retzlaff explains how the C++ compiler mangles function names and how it can be avoided in this post to the ctypes-users mailing list.

How can I help to improve this FAQ?

Send new questions, better answers, or other comments to the ctypes-users mailing list.