[Zope] replace values in a list or dictionary

[T. C. Huang]

Hi,
  How can I replace the value in a list defined in REQUEST?
  For example, in a DTML Document:
  <!--#call "REQUEST.set('L',['a',2,3,4,5])"-->
  How can I replace the value 'a' in list L with 1 so that L become
[1,2,3,4,5]?
  In Python, it's easy. L[0]=1. How can one do the same thing in Zope
DTML Document?

T.C. Huang