Check for existence?

[Gerrie Roos]

I'm very new to Python and got a very basic question:

How do I check to see if a variable exists/is available in the current
namespace?

I need to do this since I'm writing a script that gets called from Zope
and I'm not sure the vars I need are in the namespace...I might
misunderstand the whole issue, though, in which case I'll seek
assistance from the Zope list.

I've been through 'Diving into Python', the lang and lib refs, FAQ
etc...