== Using Python to test system behavior

One of the things I like about the Python interpreter is that
it is just about right for doing little system behavior tests,
like how various systems handled a [[TCP port binding issue
../programming/WhyPortBindingRestriction]]. This is because Python is
low level enough to be relatively close to the actual system, so you can
be pretty sure that what you're seeing isn't Python-specific behavior,
while at the same time being high level enough that you can do the tests
in a couple of lines.

Strictly speaking you don't need an interpreter for this, just a
language at the right level, but having an interpreter avoids the whole
drag of editing and running and re-editing and re-running and so on.

(And theoretically you can write this stuff directly in C, but I'm
certainly not familiar enough with things like the C socket API that I
can toss off test programs for this in ten minutes or less. In Python
I can bind a socket in three statements, and one of them is '_import
socket_'.)

So today when I wanted to see how _bind()_ behaved on Solaris 9,
I fired up two interpreters in two windows, and in the first I
typed:

> _>>> import socket \\
> >>> s = socket.socket(); s.bind[[(('', 4000))|]]_

and in the other I typed:

> _>>> import socket \\
> >>> s = socket.socket(); s.bind[[(('127.0.0.1', 4000))|]]_

And the Solaris 9 machine promptly spewed a traceback complaining about
'_socket.error: (125, 'Address already in use')_', just as I expected.
(Yeah, I could have done it all in one Python interpreter; I didn't feel
like seeing if Solaris did something funny if the same process was doing
both _bind()_s. (It turns out it doesn't.))