[Zope] python script trouble?

[Kate Legere]

I am calling a python script 'addToFile' from a dtml method:
<dtml-call expr="addToFile()">

the script is meant to open a pre-existing file and write to it:

   f=open('file1', 'wt',1)
   f.write('hello')
   f.close

At the moment I am just writing a test to see if it works and, it doesn't.
I get, when I view the calling dtml method,

    Error Type: NameError
    Error Value: global name 'open' is not defined

I have looked through the Python bible and am at a loss to think where I
have erred.

Kate