Tool to implement ruby-inspired DSLs in python

This weekend, I created library to aid developers in creating neat little embedded DSLs when using python, without having to do any complex parsing or anything like that. The resulting DSLs look a bit more like english than python does.

The idea for this was inspired by some ruby stuff that I’ve been using lately. I’ve been using ruby quite a bit lately, and while I am still not a huge fan of the language, I do like the idea of easy to code up DSLs that I can use to populate objects without too much effort. Since I wanted a DSL for a python project I was working on, I played with a few ideas and ended up with this tool.First, create some very basic python objects, and a file with the DSL to pass to dsltool. Here’s a sample recipe DSL for baking yummy cookies.

    author = 'Mom'
    level = 'Easy'

    with Instructions('Yummy cookies'):

        preheat_oven = '375F'

        with Ingredients:
            add += '2 1/4 cups', 'flour'
            add += '1 tsp', 'baking soda'
            add += '1 tsp', 'salt'
            add += '1 cup', 'butter'
            add += '3/4 cup', 'sugar'
            add += '3/4 cup', 'brown sugar'
            add += '1 tsp', 'vanilla extract'
            add += '2', 'eggs'
            add += '2 cups', 'chocolate chips'
            add += '1 cup', 'nuts'

And the implementation to parse that dsl is super simple:

    import dsltool

    class Ingredients(object):

        def __init__(self):
            self._items = []

        @property
        def add(self):
            return dsltool.add_to_list(self._items)

        @add.setter
        def add(self, value):
            self._items = value

    class Instructions(object):
        preheat_oven = None

        ingredients = Ingredients
        steps = Steps

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

    class Recipe(object):

        author = None
        level = None

        def __init__(self):
            self.instructions = Instructions

    if __name__ == '__main__':
        obj = dsltool.parse_dsl_file('cookies.pydsl', Recipe)

The source distribution comes with an example recipe DSL that you can play with to make tasty cookies. Submit bug reports/pull requests on github, or you can download it from pypi, or even via pip:

pip install pydsltool

Let me know if you find it useful!

One Response to “Tool to implement ruby-inspired DSLs in python”

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