Calling a DLL function from Python

Question

I want to call a function inside a DLL from Python. But I'm getting this error:

"Attribute Error function not found"

This is my code:

import os
import ctypes


os.chdir("C:\\Program Files\\Compact Automated Testing System V2.0")    

# Load DLL into memory. 
CATSDll = ctypes.WinDLL ("CATS.dll")

# Set up prototype and parameters for the desired function call. 
CATSDllApiProto = ctypes.WINFUNCTYPE (ctypes.c_uint8,ctypes.c_double) 

CATSDllApiParams = (1, "p1", 0), (1, "p2", 0), 

# Actually map the call (setDACValue) to a Python name.
CATSDllApi = CATSDllApiProto (("setDACValue", CATSDll), CATSDllApiParams)

# Set up the variables and call the Python name with them. 
p1 = ctypes.c_uint8 (1)
p2 = ctypes.c_double (4)

CATSDllApi(p1,p2)

But the DLL documentation shows a function setDACValue with ChannelId & DAC Voltage as the inputs.

The above is based on a piece of code available from StackOverflow.

I've also tried the simple method of using cdll.LoadLibrary & then calling the function, but that also gives the same error.

Can anyone suggest me what is wrong? Thanks.

Full Traceback:

Traceback (most recent call last):
  File "C:\Users\AEC_FULL\Softwares\eclipse\plugins\org.python.pydev_3.9.2.201502050007\pysrc\pydevd.py", line 2235, in <module>
    globals = debugger.run(setup['file'], None, None)
  File "C:\Users\AEC_FULL\Softwares\eclipse\plugins\org.python.pydev_3.9.2.201502050007\pysrc\pydevd.py", line 1661, in run
    pydev_imports.execfile(file, globals, locals)  # execute the script
  File "C:\Users\AEC_FULL\Saravanan\Workspace\CATS\CATS.py", line 18, in <module>
    CATSDllApi = CATSDllApiProto (("setDACValue", CATSDll), CATSDllApiParams)
AttributeError: function 'setDACValue' not found

Signature of the setDACValue

Could you provide signature of function setDACValue?

kvorobiev
– kvorobiev

2015-04-23 13:44:29 +00:00
Commented Apr 23, 2015 at 13:44 — kvorobiev
– kvorobiev, Commented Apr 23, 2015 at 13:44
Hi kvorobiev ..added the signature..

user3561075
– user3561075

2015-04-23 13:56:58 +00:00
Commented Apr 23, 2015 at 13:56 — user3561075
– user3561075, Commented Apr 23, 2015 at 13:56

kvorobiev · Accepted Answer · 2015-04-23 14:05:18Z

2

When you specifiy prototype of function you should specify not only the types of arguments, but the return type as first arg to WINFUNCTYPE. Therefore, the line

CATSDllApiProto = ctypes.WINFUNCTYPE (ctypes.c_uint8,ctypes.c_double)

should be replaced with

CATSDllApiProto = ctypes.WINFUNCTYPE (ctypes.c_uint8, ctypes.c_uint8,ctypes.c_double)

answered Apr 23, 2015 at 14:05

kvorobiev

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6 Comments

user3561075 Over a year ago

Hi @kvorobiev thanks for your input...But even after adding that 'm getting the same error.

kvorobiev Over a year ago

@user3561075 Try to use CFUNCTYPE instead of WINFUNCTYPE

kvorobiev Over a year ago

@user3561075 Could you attach your DLL file, so that I was able to check it?

user3561075 Over a year ago

I could attach the DLL file but the problem is it is dependent on some additional file which is part of a SW installation. I can share that SW, DLL as well as the documentation if we have some file sharing option.

kvorobiev Over a year ago

@user3561075 To begin with I only need DLL file. You can use any file-sharing services

|

Mark Tolonen · Accepted Answer · 2015-04-25 15:27:26Z

0

Try this. You may need to use WinDLL, but CDLL is more likely:

from ctypes import *

cats = CDLL('CATS')
cats.setDACValue.argtypes = [c_uint8,c_double]
cats.setDACValue.restype = c_uint8

cats.setDACValue(1,4)

If it still can't find setDACValue, the Microsoft tool dumpbin can be used to list the exported functions names in the DLL:

dumpbin /exports CATS.dll

It comes with Visual Studio installs in the VC\bin directory under the installation.

answered Apr 25, 2015 at 15:27

Mark Tolonen

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1 Comment

user3561075 Over a year ago

Hi @Mark Tolonen : I tried to to export the functions inside the DLL using DLL Export tool & PE Explorer. I'm not able to get the functions in neither of those tools.

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