string interpolation for python

[mwilson at the-wire.com]

Yingjie Lan wrote:
> Seems you miss understood my notion of dynamic string.
> Dynamic strings are expressions in disguise: the things
> in between $...$ are plain old expressions (with optional
> formatting specifications). They are evaluated
> as if they were outside the dynamic string. 
 In that case you should re-think the delimiters, so that you have something 
that can be nested.  An example (example only, I'm not in love with it as a 
final form):

"A string that gets %(count*spacer%) in the middle"

"A string that gets %(count*%(spacer%)%) in the middle"

	Mel.