(Requirement: homebrew should already be installed) This will install opencv3 on a mac for use with python2
$ brew tap homebrew/science
$ brew install opencv3 --with-python3
$ mkdir -p /Users/rushi/Library/Python/2.7/lib/python/site-packages
$ echo 'import sys; sys.path.insert(1, "/usr/local/lib/python2.7/site-packages")' >> /Users/rushi/Library/Python/2.7/lib/python/site-packages/homebrew.pth
$ echo 'import site; site.addsitedir("/usr/local/lib/python2.7/site-packages")' >> /Users/rushi/Library/Python/2.7/lib/python/site-packages/homebrew.pth