CODEWITHSUNDEEP
pythondllimportctypes
Sam
Sam

Reputation: 565

How can I use a DLL from Python

I am trying to load a DLL in Python, I want to use its eConnect() function using ctypes

What I know from the source code of the DLL:

I tried to access the eConnect from two ways myfunction and myfunction2, but I probably get it wrong. Here is my code:

from ctypes import *

def main():

IP = c_char_p('127.0.0.1')
port = c_uint(7496)
client_id = c_int(0)

myfunction = getattr(cdll.TwsSocketClient, "?eConnect@EClientSocket@@UAE_NPBDIH@Z")
myfunction2= cdll.TwsSocketClient[6]

print myfunction
print myfunction2

print myfunction(IP, port, client_id,IP)

if __name__ == "__main__":
main()

I get the below error:

"WindowsError: exception: access violation reading 0x0000002D"

I would badly need some help here (I do not know c++). Thanks!

Upvotes: 0

Views: 2252

Answers (5)

Sam
Sam

Reputation: 565

Thanks for your answers everyone. I took Adam's advise and reconsidered my approached. As I do not know know c++, it was a bad idea from the start.

There is an alternative API in R (not official) which is built on top of the official Java API. It is then quite easy to link R and Python using rPy2.

Upvotes: 0

Adam Rosenfield
Adam Rosenfield

Reputation: 400642

The function being exported is a class member function of the class EClientSocket. You're attempting to call that function from Python without passing in an EClientSocket pointer as the this parameter; furthermore, ctypes doesn't know anything about the __thiscall calling convention, so even if you did pass in an EClientSocket instance, it would be on the stack instead of in the ECX register.

The only real solution to this would be to export a C wrapper from your DLL that forwards the call to eConnect. For example:

extern "C" DLLEXPORT
bool EClientSocket_eConnect(EClientSocket *This, const char *host, UINT port, int clientId)
{
    return This->eConnect(host, port, clientId);
}

However, even in that case, you have to be extra-careful on the Python side to construct an appropriate EClientSocket instance. I'd strongly recommend reconsidering your approach here.

Upvotes: 1

Fábio Diniz
Fábio Diniz

Reputation: 10363

There is also Boost::Python

Upvotes: 0

inspectorG4dget
inspectorG4dget

Reputation: 114035

Consider looking into IronPython. It makes it easier to call on DLL files.

Upvotes: 0

Jeremy Whitlock
Jeremy Whitlock

Reputation: 3818

To make things easier, more Pythonic, you might want to look into ctypesgen:

http://code.google.com/p/ctypesgen/

It will generate proper wrapper functions, data types and such for you. If you just want to know how to use ctypes, might as well start with the tutorial:

http://docs.python.org/library/ctypes.html

Anything more specific and I'll have to read the API for the DLL you're attempting to use.

Upvotes: 4

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