Command lookup is slow

[jlisee]

While looking to use plumbum to replace shell scripts at my organization everything was looking great until I noticed the slow execution speed. This simple one line command takes 650ms to execute on my machine:

time python -c "from plumbum.cmd import grep, wc, cat, head, ls, touch, mkdir, rm, echo, dd"

One of the biggest offenders appears to be slow "which" speed. You can see this in the results from this benchmark program I made:

# cmds: grep, wc, cat, head, ls, touch, mkdir, rm, echo, dd
from plumbum import local: 0.01800
twisted.python.procutils.which: 0.00042
plumbum local.which: 0.33167
from plumbum.cmd import: 0.62665

Here is the program: https://gist.github.com/jlisee/7443118

Platform details: Python 2.7.3, Ubuntu 12.04, 32 bit, Core i7 @ 2.4GHz

Any ideas how to fix this?