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Before a Django TemplateResponse is rendered, modify the context data in-place with context-processor like functionality

Project description

Author: Keryn Knight
Version: 0.1.1
Release Status
stable (0.1.1) travis_stable
master travis_master

What it does

Ever used Django and wished you could have a context processor which received the existing context, along with the request, so that it could do different things depending on the values the view provided? This does that, as long as you’re using TemplateResponse objects and not render() or render_to_response().

Installation

You can use pip to install the 0.1.1 version from PyPI:

pip install django-contextaware-processors==0.1.1

Or you can grab it from GitHub like this:

pip install -e git+https://github.com/kezabelle/django-contextaware-processors.git#egg=django-contextaware-processors

Usage

Add a new CONTEXTAWARE_PROCESSORS setting to your project configuration. It should be an iterable of strings representing the dotted paths to your processors, just the same as the Django context processors are configured:

CONTEXTAWARE_PROCESSORS = ('path.to.my_processor', 'another_processor.lives.here')

Processors are executed in the order in which they are declared, and update the original context data. The new context is given to subsequent processors, such that the last processor above (another_processor.lives.here) will see any changes made by path.to.my_processor.

Using the middleware

In most cases, if you’re using TemplateResponse objects (or any Class Based View which uses them for you), you want to use the provided middleware:

MIDDLEWARE_CLASSES = (
    # ...
    'contextaware_processors.middleware.ContextawareProcessors',
    # ...
)

As this makes use of process_response(request, response) you probably want it somewhere near the bottom, so that it modifies the context on the way out as soon as possible. The middleware will automatically apply any processors defined in CONTEXTAWARE_PROCESSORS

Using the TemplateResponse subclass

For custom situations, there is context_processors.response.ContextawareTemplateResponse class which exposes an add_context_callback(callback_function) which can be used to apply view-specific context modifiers, though why you’d need to is not immeidiately obvious to me ;) If the ContextawareProcessors middleware notices a ContextawareTemplateResponse it will add those defined in CONTEXTAWARE_PROCESSORS after any previously registered custom modifiers.

Writing a context-aware processor

The API contract for a processor is the same as a normal context processor, but with the addition of a context parameter, sent as a named-kwarg.

A normal context processor looks like:

def my_processor(request):
    return {'MY_VALUE': 1}

While a context-aware processor looks like:

def my_processor(request, context):
    if 'MY_KEY' in context:
        return {'MY_VALUE': 2}
    return {'MY_VALUE': None}

Return values

A context-aware processor must return one of 3 things: - A dictionary to .update(...) the existing context with, - NotImplemented may be used to mark it as irrelevant for the request - For convienience, None may also be used to skip updating the context.

Supported Django versions

The tests are run against Django 1.8 through 1.10, and Python 2.7, 3.3, 3.4 and 3.5.

Running the tests

If you have a cloned copy, you can do:

python setup.py test

If you have tox, you can just do:

tox

Contributing

Please do!

The project is hosted on GitHub in the kezabelle/django-contextaware-processors repository.

Bug reports and feature requests can be filed on the repository’s issue tracker.

If something can be discussed in 140 character chunks, there’s also my Twitter account.

The license

It’s FreeBSD. There’s should be a LICENSE file in the root of the repository, and in any archives.


Copyright (c) 2017, Keryn Knight All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
  2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


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