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https://github.com/greenbankobservatory/django-settings-diff

A very simple tool to help diff two Django settings modules
https://github.com/greenbankobservatory/django-settings-diff

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A very simple tool to help diff two Django settings modules

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``django-settings-diff``

========================



A very simple tool to help diff two Django settings modules.



Motivation

----------



Let's say that you have done some significant refactoring to your settings module. For example, you have gone from a single settings file to a modular approach, where there is no longer a single ``settings.py``. You want to make sure that your settings are effectively *exactly* the same as before, though! Of course you can't rely on simple file diffing, since there is no longer a single ``settings.py``.



There are some non-intuitive things to account for, which ``django-settings-diff`` handles for you:



1. Even with a single ``settings.py``, there is a (potentially) significant difference between simply importing the file and the "final" settings that are used by Django (see https://docs.djangoproject.com/en/2.1/topics/settings/#using-settings-in-python-code). That is, we want to compare the *actual settings at runtime*!

2. The ``settings`` object cannot be naively treated as a ``dict`` -- it is similar, but different enough to prevent easy diffing (the native settings object thwarts both ``pprint`` and ``deepdiff``).



So, it isn't doing anything crazy, but it removes some overhead.



Installation

------------



Install from pip (recommended):



::



    $ pip install django-settings-diff



Or, install straight from the repo:



::



    $ git clone https://github.com/GreenBankObservatory/django-settings-diff

    $ pip install django-settings-diff



Note that this will install a wrapper script for you: ``diffsettings``



Entry Points

------------



Use the wrapper script (recommended):



::



    $ diffsettings -h



Call the module:



::



    $ python -m django_settings_diff -h



Import as library:



::



    $ python

    >>> from django_settings_diff import diffsettings

    >>> help(diffsettings)



Usage

-----



There are two standard usage patterns.



You should first ensure that you have saved two versions of your settings. For this example we will use ``myapp/settings_old.py`` and ``myapp/settings_new.py``.



Alternatively, you could use the same ``DJANGO_SETTINGS_MODULE`` for both dumps, but swap the settings file itself in between. This is useful in repositories that rely on the settings file being a specific name, for example.



#1: Compare Python objects directly

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



This uses ``deepdiff`` internally to perform the diff.



Dump Settings

^^^^^^^^^^^^^



Pickle the settings modules to disk:



::



    $ DJANGO_SETTINGS_MODULE=myapp.settings_old diffsettings --dump old_settings.pkl

    $ DJANGO_SETTINGS_MODULE=myapp.settings_new diffsettings --dump new_settings.pkl



Diff Settings

^^^^^^^^^^^^^



Now we can diff the two settings objects:



::



    $ diffsettings old_settings.pkl new_settings.pkl 



See the documentation for `deepdiff `_ for help deciphering the output.



#2: Compare via external diff tool

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



In this method the settings are dumped as text files and then compared using a standard diff tool.



Dump Settings

^^^^^^^^^^^^^



Dump the settings modules to disk (internally this uses ``pprint`` to print the settings object):



::



    $ DJANGO_SETTINGS_MODULE=myapp.settings_old diffsettings --dump old_settings.txt

    $ DJANGO_SETTINGS_MODULE=myapp.settings_new diffsettings --dump new_settings.txt



Diff Settings

^^^^^^^^^^^^^



Then, use your favorite diff tool to compare these. This should work quite well, since the object hierarchy has been broken up line by line.



For example:



::



    $ tkdiff {old,new}_settings.txt