The dll created by Boost.Python cannot be imported (following Boost Python's QuickStart)

Question

I'm trying to follow the instructions here to use the Boost.Python. The source code is in that webpage. I can compile, link this simple sample code but I cannot import the resulting module in python command line. It always error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named hello_ext

I have no idea what the matter is because that page just says: "That's it. We're done. We can now build this as a shared library. The resulting DLL is now visible to Python." This is my building environment:

• Windows 7 64 bit, I am the Administrator and run cmd as Administrator
• boost version is 1.64.0 (precompiled binary boost_1_64_0-msvc-14.0-64.exe downloaded from here)
• python version is 2.7.13, 64 bit
• Visual studio 2015, Update 3
• The target is a DLL
• The project name is ConsoleApplication1, so the output is ConsoleApplication1.dll. I have changed the filename to hello_ext.dll but same error.
• I built with x64 configuration and I have verified with dumpbin that the output ConsoleApplication1.dll is really 64 bit
• I have added the path ......\ConsoleApplication1\x64\Release which contains ConsoleApplication1.dll into sys.path inside python command line.

So, could you please tell me how to import the module in python? Thanks a lot.

Answer 1

I solved the problem myself. Thank jagerman for his useful suggestions.

(1) Just change the output filename from ConsoleApplication1.dll to hello_ext.pyd. You can automate this rename by setting Pages->General->Target Extension to ".pyd". Make sure the file hello_ext.pyd is in python's search path. You can just throw it to C:\Python27\DLLs which is one of python's built-in search paths.

(2) Now you will got a different import error: DLL load failed: The specified module could not be found. If you look closely at the file size of hello_ext.pyd, you'll likely notice something wired -- it's only 19KB. That means it doesn't contain everything needed to import into python, so python has to find the missing part to properly import it. Yes, you may guess that -- the only possible missing stuff is Boost.Python libraries, so add path to it into PATH environment variable -- for me, it is C:\local\boost_1_64_0\lib64-msvc-14.0.

Then the problem is solved. Note: some answers in other related questions may suggest build as a static library, That way, you will got another import error: DLL load failed: %1 is not a valid Win32 application. So just build as DLL. PS: you don't need to specify boost_python-vc140-mt-1_64.lib or boost_python-vc140-mt-gd-1_64.lib in Property Pages->Linker->Input->Additional Dependencies as some comments suggested.