I still cannot get PyDev and eclipse on MacOS to reliably import modules.
import csv generates an “Unresolved import:” error within PyDev; however, when I open Terminal and run the script from the interpreter it works fine.
PyDev is using the interpreter found at /usr/bin/python, which is pointing to Python 2.7.
The relevant files (csv.pyc and csv.pyo) are in /System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7, which is in PYTHONPATH.
Actually, for the standard library, PyDev needs the .py files (from your description you only have the .pyc/.pyo files) — it should give you a big warning when you try to configure an interpreter where the .py files are not available.
So, the recommended solution would be using a python distribution from http://python.org (instead of the default which comes with Mac OS) or grab the standard library from elsewhere and copy it over to where you have the standard library in Mac OS.
See the “IMPORTANT for Mac users” note at: http://pydev.org/manual_101_interpreter.html