Can Python call Delphi functions in a DLL?

Question

I am trying to call functions from a DLL which seems to be created in Delphi. An example of a some functions supported by the DLL are:

function oziDeleteWpByName(var name:pansichar):integer;stdcall

The Python code I have written to access the above functions is not working.

from ctypes import *
libc = cdll.OziAPI
name ='test'

pi = pointer(name)

delname = libc.oziDeleteWpByName

delname(name)

It seems I am passing the wrong data type to the function. Any ideas on how to do it right?

Thanks it worked. Now please help with this function:

function oziGetOziVersion(var Version:pansichar;var DataLength:integer):integer;stdcall; The version of OziExplorer is returned in the Version variable.

Now how do I pass 'var version' when it the one which will also be returned.

var name:pansichar implies that the name parameter can be modified and returned to the caller. Does the function really do that? Are you planning to read the contents of name after the function returns? — David Heffernan
– David Heffernan, Commented Jan 9, 2012 at 15:03
Also, which version of Python are you using? Can make a difference to string encodings. — David Heffernan
– David Heffernan, Commented Jan 9, 2012 at 15:06
yeah, that var declaration is fishy. If you, user 1138... wrote that DLL, why did you do that? — Warren P
– Warren P, Commented Jan 9, 2012 at 15:07

David Heffernan · Accepted Answer · 2012-01-09 15:15:17Z

13

from ctypes import *

# Not strictly needed but it's good to be explicit.
windll.OziAPI.oziDeleteWpByName.argtypes = [POINTER(c_char_p)]
windll.OziAPI.oziDeleteWpByName.restype = c_int

p = c_char_p('test')
retval = windll.OziAPI.oziDeleteWpByName(byref(p))

edited Jan 9, 2012 at 15:15

David Heffernan

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answered Jan 9, 2012 at 15:01

yak

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2 Comments

yak Over a year ago

Updated with argtypes and restype.

ABM Over a year ago

My python isn't able to find windll.OziAPI - stackoverflow.com/questions/27910191/…

Mason Wheeler · Accepted Answer · 2012-01-09 14:54:58Z

1

In Delphi, a var parameter is passed by reference. So what you have there is a pointer to a PAnsiChar (aka C-style string pointer). If you're passing it a string pointer, instead of a pointer to a string pointer, it won't work.

answered Jan 9, 2012 at 14:54

Mason Wheeler

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5 Comments

LaKraven Over a year ago

I also don't see in that Python code anything which suggests you're specifying the stdcall calling convention. Doesn't cdll in Python default to cdecl? If so, this will also cause you problems!

Warren P Over a year ago

I'm pretty sure that anything you invoke via a dll and which the python runtime library loads and invokes, will always use the windows standard calling conventions.

David Heffernan Over a year ago

@Warren No, LaKraven is right. cdll vs windll is the way to specify calling conventions. Also, there is no Windows standard for calling convention, at least on x86. Some libraries use stdcall and some use cdecl. Think of msvcrt for example. It's all cdecl.

Warren P Over a year ago

Oh right. My bad. I am so Delphi centric that I think of stdcall as a Windows standard but it isn't. It's kind of the usual thing for "visual basic and delphi guys".

LaKraven Over a year ago

@DavidHeffernan That's the first time you and I have agreed today :)

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