opencv-python: DLL load fails on Anaconda/Windows install (python3.dll)

After doing a simple pip install opencv-python or pip install opencv-contrib-python and trying to import the library, I ran into this issue:

λ python
Python 3.5.2 |Anaconda 4.2.0 (64-bit)| (default, Jul  5 2016, 11:41:13) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import cv2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Anaconda3\lib\site-packages\cv2\__init__.py", line 7, in <module>
    from . import cv2
ImportError: DLL load failed: The specified module could not be found.

The readme suggests installing the Visual C++ Redistributable for Visual Studio 2015 but I already had it installed (actually had Visual Studio itself installed as well).

Checking the dependencies of the pyd binary in this package (using dumpbin which comes with Visual Studio):

λ dumpbin.exe C:\Anaconda3\Lib\site-packages\cv2\cv2.cp35-win_amd64.pyd /IMPORTS | grep dll
    python3.dll
    python35.dll
    MSVFW32.dll
    AVIFIL32.dll
    AVICAP32.dll
    KERNEL32.dll
    USER32.dll
    GDI32.dll
    ole32.dll
    OLEAUT32.dll
    COMDLG32.dll
    ADVAPI32.dll

After checking if these were in the PATH I was surprised to find that python3.dll was the only one that wasn’t!

Although python3.dll comes with the standard CPython install, it’s not packaged with Anaconda for some reason. ContinuumIO/anaconda-issues#1394 references this and it seems like it’s just not supported(?).

As a workaround suggested in that thread, I solved this by just copying python3.dll from the official CPython 3.5.2 binaries (specifically from the Windows x86-64 embeddable zip file) into C:\Anaconda3, although I imagine it would work being anywhere in your PATH.

I thought I’d share this bit of troubleshooting since Anaconda is a popular distribution among academics and so is OpenCV, so I figure I might not be the only one running into this issue. Maybe a note in the readme might help others until Anaconda resolves this?

Alternatively, the menpo/opencv3 Anaconda package would also work but I don’t think it supports ffmpeg nor opencv-contrib.

For reference, I’m running on Python 3.5.2 which came with Anaconda 4.2.0 (official installer), although conda info reports a slightly newer version:

λ conda info
Current conda install:

               platform : win-64
          conda version : 4.3.16
       conda is private : False
      conda-env version : 4.3.16
    conda-build version : 2.0.2
         python version : 3.5.2.final.0
       requests version : 2.12.4
       root environment : C:\Anaconda3  (writable)
    default environment : C:\Anaconda3
       envs directories : C:\Anaconda3\envs
                          C:\Users\Talmo\AppData\Local\conda\conda\envs
                          C:\Users\Talmo\.conda\envs
          package cache : C:\Anaconda3\pkgs
                          C:\Users\Talmo\AppData\Local\conda\conda\pkgs
           channel URLs : https://repo.continuum.io/pkgs/free/win-64
                          https://repo.continuum.io/pkgs/free/noarch
                          https://repo.continuum.io/pkgs/r/win-64
                          https://repo.continuum.io/pkgs/r/noarch
                          https://repo.continuum.io/pkgs/pro/win-64
                          https://repo.continuum.io/pkgs/pro/noarch
                          https://repo.continuum.io/pkgs/msys2/win-64
                          https://repo.continuum.io/pkgs/msys2/noarch
            config file : None
           offline mode : False
             user-agent : conda/4.3.16 requests/2.12.4 CPython/3.5.2 Windows/10 Windows/10.0.15063

Cheers and thanks for all the work you put into this repo!