Can’t install psycopg2 package through pip install on MacOS

I fixed this by installing Command Line Tools

xcode-select --install

then installing openssl via Homebrew and manually linking my homebrew-installed openssl to pip:

env LDFLAGS="-I/usr/local/opt/openssl/include -L/usr/local/opt/openssl/lib" pip install psycopg2

on macOS Sierra 10.12.1