How can I use a DLL file from Python?

Question

What is the easiest way to use a DLL file from within Python?

Specifically, how can this be done without writing any additional wr

Answer 1

Building a DLL and linking it under Python using ctypes

I present a fully worked example on how building a shared library and using it under Python by means of ctypes. I consider the Windows case and deal with DLLs. Two steps are needed:

1. Build the DLL using Visual Studio's compiler either from the command line or from the IDE;
2. Link the DLL under Python using ctypes.

The shared library

The shared library I consider is the following and is contained in the testDLL.cpp file. The only function testDLL just receives an int and prints it.

#include 
​
extern "C" {
​
__declspec(dllexport)
​
void testDLL(const int i) {
    printf("%d\n", i);
}
​
} // extern "C"

Building the DLL from the command line

To build a DLL with Visual Studio from the command line run

"C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\Tools\vsdevcmd"

to set the include path and then run

cl.exe /D_USRDLL /D_WINDLL testDLL.cpp /MT /link /DLL /OUT:testDLL.dll

to build the DLL.

Building the DLL from the IDE

Alternatively, the DLL can be build using Visual Studio as follows:

1. File -> New -> Project;
2. Installed -> Templates -> Visual C++ -> Windows -> Win32 -> Win32Project;
3. Next;
4. Application type -> DLL;
5. Additional options -> Empty project (select);
6. Additional options -> Precompiled header (unselect);
7. Project -> Properties -> Configuration Manager -> Active solution platform: x64;
8. Project -> Properties -> Configuration Manager -> Active solution configuration: Release.

Linking the DLL under Python

Under Python, do the following

import os
import sys
from ctypes import *

lib = cdll.LoadLibrary('testDLL.dll')

lib.testDLL(3)