Middleware for Python

Copyright (c) 2016 David Betz

Installation

pip install middleware

Compatibility

Python 2 and 3

Purpose

Most everyone needs a concept of middleware.

Following are examples of using this, see test_middleware.py for full examples.

class AdditionMiddleware1(Middleware):
    def create(self):
        def func(mwa, context):
            try:
                counter = context['counter']
            except:
                counter = 0
            context['counter'] = counter + 1

            return next(mwa)

        return func

When using a class, add a create function which returns a function. This inner fuction accepts the middleware array and the data context and returns next(mwa) to create a middleware chain.

For this example, I'll add two more:

class AdditionMiddleware2(AdditionMiddleware1):
    pass


class AdditionMiddleware3(AdditionMiddleware2):
    pass

Now to run it. Use set to set an array of middleware and add to add one to the array. set overwrites everything. That's just what set means.

    handler = Handler()
    handler.set([AdditionMiddleware1, AdditionMiddleware2])
    handler.add(AdditionMiddleware3)
    handler.execute()

    # handler['counter'] == 3

In this case, there is no initial context and each of the three middleware increment a counter ending with handler['counter'] == 3.

You can skip the entire class stuff too:

handler = Handler()
def inline(wma, context):
    context['myvalue'] = 12
handler.add(inline)
handler.execute()
# handler['myvalue'] == 12

Use the following to send initial context:

handler = Handler(counter=1)

It's actually kwargs, so you can load it up:

handler = Handler(**{'a': 1, 'b': 2})
def inline(wma, context):
    context['a'] = context['a'] + context['b']
handler.add(inline)
handler.execute()