Quick DSL example for Python

dsl.py

from __future__ import print_function
from contextlib import contextmanager


class DslRunner(object):
    """Runs Python code in the context of a class.

    Public methods will be exposed to the DSL code.
    """

    def __init__(self, contextclass):
        self.contextclass = contextclass


    def make_context(self):
        ctx = self.contextclass()
        ctxmap = {}
        method_names = [fun for fun in ctx.__class__.__dict__ if not fun.startswith('_')]
        methods = ctx.__class__.__dict__

        def method_caller(fun):
            unbound = methods[fun]
            def wrapped(*args, **kw):
                args = (ctx,) + args
                return unbound(*args, **kw)
            return wrapped

        for fun in method_names:
            ctxmap[fun] = method_caller(fun)

        return (ctx, ctxmap)

    def execfile(self, filename):
        ctx, ctxmap = self.make_context()
        execfile(filename, {}, ctxmap)
        return ctx


class MyContext(object):
    """DSL Context class. All methods not starting with an underscore
    are exposed."""


    def __init__(self):
        self.cities = []
        self.bars = []


    def bar(self, name):
        self.bars.append(name)


    @contextmanager
    def city(self, name):
        self.cities.append(name)
        yield
        print("back from city %r" % name)


if __name__ == "__main__":
    import sys
    ctx = DslRunner(MyContext).execfile(sys.argv[1])
    print("cities:", ctx.cities)
    print("bars:", ctx.bars)

example.dslcode

bar("room minibar")
with city("Vienna"):
   bar("Silver Bar")
   bar("D Bar")
   bar("Rosengarten")