Install libpq-dev on Mac OS X

I'm trying to run Django with a Postgresql backend on my local Mac OS X. I've installed Django using pip:

sudo pip install Django

I've installed Postgresql with one of the binary installers here.

But when I try to install psycopg2 I get an error (pasted below) that it can't find pg_config.

From this question it seems like I should install libpq-dev but I'm not sure how.

I've tried installing libpqxx with MacPorts, but that hasn't done anything.

How do I get libpg-dev installed? Or is there something else I'm missing?

henrietta:~ $ pip install psycopg2
Downloading/unpacking psycopg2
  Downloading psycopg2-2.4.5.tar.gz (719Kb): 719Kb downloaded
  Running setup.py egg_info for package psycopg2
    Error: pg_config executable not found.

    Please add the directory containing pg_config to the PATH
    or specify the full executable path with the option:

        python setup.py build_ext --pg-config /path/to/pg_config build ...

    or with the pg_config option in 'setup.cfg'.
    Complete output from command python setup.py egg_info:
    running egg_info

creating pip-egg-info/psycopg2.egg-info

writing pip-egg-info/psycopg2.egg-info/PKG-INFO

writing top-level names to pip-egg-info/psycopg2.egg-info/top_level.txt

writing dependency_links to pip-egg-info/psycopg2.egg-info/dependency_links.txt

writing manifest file 'pip-egg-info/psycopg2.egg-info/SOURCES.txt'

warning: manifest_maker: standard file '-c' not found

Error: pg_config executable not found.



Please add the directory containing pg_config to the PATH

or specify the full executable path with the option:



    python setup.py build_ext --pg-config /path/to/pg_config build ...



or with the pg_config option in 'setup.c