[Chicago] Install problems with numpy via pip on Snow Leopard (Mac OS X 10.6.x)

[Skip Montanaro]

I'm having no luck getting numpy to build and install properly on my
Mac.  I'm doing this in a Django virtualenv.  I've tried both of these
commands to install it:

    pip install numpy

and

    ARCHFLAGS="-arch x86_64" pip install numpy

Both -- after emitting a rather amazing number of warning messages --
manage to install numpy, but import attempts fail with the following
error:

    ImportError:
dlopen(/Users/skip/django/mysite/venv/lib/python2.7/site-packages/numpy/core/multiarray.so,
2): no suitable image found.  Did find:
	/Users/skip/django/mysite/venv/lib/python2.7/site-packages/numpy/core/multiarray.so:
mach-o, but wrong architecture

Python is 2.7.2+ (yes, I should update):

    % python
    Python 2.7.2+ (2.7:527c40add91d, Jun 12 2011, 15:36:59)
    [GCC 4.0.1 (Apple Inc. build 5493)] on darwin
    Type "help", "copyright", "credits" or "license" for more information.

and comes from my venv environment.

Gcc is in /usr/bin and reports as

   % gcc -version
   i686-apple-darwin10-gcc-4.2.1: no input files

I have this vague recollection that gcc 4.2 was problematic.

Anybody encounter and solve this problem already?  Google was no help,
though if you have a LMGTFY link, I'd be happy to be chastised for
feeble Google-fu.

Thx,

Skip Montanaro