[Zope] Typecasting in DTML (or is this Python?)

[Julian Clark]

Hello again list...

I need to typecast [amount] as a string - but only within the history string.
in my attempt below, history finished up as....

Advertising authority number 25020030718 For $['amount']

Where I need amount to show up as the specific amount.

<dtml-call "REQUEST.set('amount',_['amount'])">
<dtml-call "REQUEST.set('history',_['history1'] + REQUEST['authority'] + ' For $' + _.str(['amount']))">

I've tried a few variants, but not had much joy.

Any help would be fantastic... thanks in advance

Julian