parse an environment file

[Jason Friedman]

$ crontab -l
* * * * * env

This produces mail with the following contents:

HOME=/home/spjsf
LOGNAME=spjsf
PATH=/usr/bin:/bin
PWD=/home/spjsf
SHELL=/bin/sh
SHLVL=1
USER=spjsf
_=/usr/bin/env

On the other hand

$ env

produces about 100 entries, most of which are provided by my .bashrc;
cron provides only a limited number of environment variables.

I want my python 3.2.2 script, called via cron, to know what those
additional variables are.  How?