WindowsError: [Error 126] when loading a DLL with ctypes

Question

This works fine on Windows 7 with Python 2.7:

lib = ctypes.cdll.LoadLibrary(\'prov_means\')
provmeans = lib.provmeans  

The library prov_me

Answer 1

Which compiler did you use to build the library? Maybe some required libraries are missing? You can check what dependencies the library has with Dependency Walker (http://www.dependencywalker.com/)?

Answer 2

Error 126 is what you get when a dependent DLL can not be found. There are two obvious causes for this:

1. Your DLL is not being located.
2. Your DLL depends on other DLLs that cannot be found.

I doubt that option 1 is the problem but in any case I think I would probably be using a full path to that DLL to be sure.

So that leaves option 2 and the most common cause for that is that your target machine does not have the C++ runtime installed. Either install the C++ runtime on your target machine, or use static linking, /MT, when building your DLL so that you do not need to redistribute the runtime.

Probably, on the machine that you developed the DLL, you have installed a C++ compiler and that installed the runtime for you. On your target machine, where the code fails, you have not installed the compiler and so the runtime is not present.