Inferior process mystery

[Dave Abrahams]

Any of the following will launch /opt/local/bin/python, which is in my
PATH:

 * `M-! python RET'
 * `M-! python& RET'
 * `M-x shell RET python RET'
 * `C-u M-x run-python RET env python RET'

However, although the variable `python-command' has the value "python",
either of these will launch /usr/bin/python:

 * `M-x run-python'
 * `C-u M-x run-python RET python RET'

I'm at a loss to explain why python-command is not selecting the same
Python that's in my PATH and run by env.  Can someone explain why this
is happening?

Many thanks in advance,

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com