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DSLs in Python

From: andrew cooke <andrew@...>

Date: Thu, 8 Sep 2011 20:40:38 -0300

DSLs are not that easy in Python - the language isn't as flexible as, say,
Haskell (where function application is "invisible") or Ruby (with blocks).
these are some of the tricks i've used in the past:

 - Method Chaining.  Not that wonderful, but better than nothing.
     http://en.wikipedia.org/wiki/Method_chaining

 - Operators.  This is typically the best approach, but sometimes looks
     artificial.  Operators are translated into method calls on the argument
     to the left.  so something like `foo & bar` is equivalent to
     `foo.__and__(bar)`.

 - With Contexts.  A bit more esoteric.  On the exit from the "with" you
     can access the enclosing scope and use introspection to do various
     things.  See the `with TraceVariables()` here
     http://www.acooke.org/lepl/debugging.html#variable-traces for an example
     - that inspects the scope, find all the variable used, and modifies the
     objects associated with them (sets a flag that enables debugging).

Alternatives that might make more sense could include:

 - A configuration file with a separate syntax.  XML went out of fashion
     just as it the tools were becoming powerful enough to make it fun - Mule
     (the ESB) has an XML configuration language in XML that is very
     expressive,  compact and type safe (or was when i wrote it ;o).

 - Decorators and documentation strings / attributes.  Perhaps not
     relevant here, but these let you stay within python while adding more
     metadata.  See this question for how attributes are used in Django -
     http://stackoverflow.com/questions/7337681/method-attributes-in-django

Andrew

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