DTML Methods are standard Zope objects usually used as dynamic templates; similar to ASP and PHP. See also DTML, DTMLDocument, Page Templates.
DTML is still useful for templating plain text such as emails or ZSQL Methods s, or when speed is a concern. Otherwise it should generally be avoided for structural markup in favor of Page Templates.
From a python script one can add a DTML Method by the following command:
context.manage_addDTMLMethod(Id, title)
Is there a possibility to change the contents of a DTML-Method by a python script? Certainly, check the source or API documentation.