You can download the latest OpenCV 3.2.0 for Python 3.6 on Windows 32-bit or 64-bit machine, look for file starts withopencv_python‑3.2.0‑cp36‑cp36m, from this unofficial site. Then type below command to install it:
pip install opencv_python‑3.2.0‑cp36‑cp36m‑win32.whl (32-bit version)
pip install opencv_python‑3.2.0‑cp36‑cp36m‑win_amd64.whl (64-bit version)
I think it would be easier.
Update on 2017-09-15:
OpenCV 3.3.0 wheel files are now available in the unofficial site and replaced OpenCV 3.2.0.
Update on 2018-02-15:
OpenCV 3.4.0 wheel files are now available in the unofficial site and replaced OpenCV 3.3.0.
Update on 2018-06-19:
OpenCV 3.4.1 wheel files are now available in the unofficial site with CPython 3.5/3.6/3.7 support, and replaced OpenCV 3.4.0.
Update on 2018-10-03:
OpenCV 3.4.3 wheel files are now available in the unofficial site with CPython 3.5/3.6/3.7 support, and replaced OpenCV 3.4.1.
Update on 2019-01-30:
OpenCV 4.0.1 wheel files are now available in the unofficial site with CPython 3.5/3.6/3.7 support.
Update on 2019-06-10:
OpenCV 3.4.6 and OpenCV 4.1.0 wheel files are now available in the unofficial site with CPython 3.5/3.6/3.7 support.
src : https://stackoverflow.com/a/43190144/13319197