Python Simple Settings

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.. _description:

A simple way to manage your project settings.

simple-settings is inspired by Django's settings system but is generic for any python project.

With simple-settings you just need to specify your settings module using the --settings command line arg when invoking your python script (or SIMPLE_SETTINGS environment var) and all settings will be exposed as properties of the simple_settings.settings module.

.. code:: python

>>> from simple_settings import settings
>>> print(settings.FOO)
'some value in foo'

Installation

simple-settings is available on Pypi <https://pypi.python.org/pypi/simple-settings>__.

.. code:: bash

$ pip install simple-settings

..

To install simple-settings with all dependencies use ``pip install simple-settings[all]``

simple-settings is tested with Python 2.7, 3.4, 3.5, 3.6 and PyPy.

How this works

simple-settings reads and stores all variables (or constants if you prefer) of a python module that you specify. To store your settings you need at least one setting file (in any of supported formats).

To specify your settings module you have two approaches: with command line or environment.

For example, imagine that you have a python module for your project settings and this file is in "settings/development.py\ " (a common example). To load settings of this file you can run your project with command line arg --settings:

.. code:: bash

$ python app.py --settings=settings.development

simple-settings accepts --simple-settings command line arg also. Or set the environment variable SIMPLE_SETTINGS:

.. code:: bash

$ export SIMPLE_SETTINGS=settings.development
$ python app.py

..

the ``settings`` environment variable is deprecated

The simple_settings.settings object reads both the command line and environment in this order (but simple-settings takes the first value it encounters), to know which file to load.

Another option is use class LazySettings instead of singleton object settings. With LazySettings class is possible to determine settings files in object create:

.. code:: python

from simple_settings import LazySettings


settings = LazySettings('settings.development')

If you don't pass any value in LazySettings init argument, this class follow the same behavior of settings object.

Example

This is a very dummy example, in real world you would use simple-settings in more complex cases.

project_settings.py

In this example we just store a simple string but any python type is
accepted.

.. code:: python

    SIMPLE_CONF = 'simple'

**app.py**
~~~~~~~~~~

You don't need specify which setting *simple-settings* must load, you
can do this with command line or environment.

.. code:: python

    from simple_settings import settings

    print(settings.SIMPLE_CONF)

**Run**
~~~~~~~

You can specify your settings module with command line:

.. code:: bash

    $ python app.py --settings=project_settings
    simple

Or environment:

.. code:: bash

    $ export SIMPLE_SETTINGS=project_settings
    $ python app.py
    simple

Check
`examples <https://github.com/drgarcia1986/simple-settings/tree/master/examples>`__,
in project repository for more usage samples.

as\_dict()
----------

You can check the loaded settings through method ``settings.as_dict()``

.. code:: python

    >>> settings.as_dict()
    {'SIMPLE_CONF': 'simple'}

configure
---------

You can change any settings (and add new settings) in runtime with
method ``configure``:

.. code:: python

    >>> settings.SOME_CONF
    foo
    >>> settings.configure(SOME_CONF='bar')
    >>> settings.SOME_CONF
    bar


Keep in mind that this only modifies the settings during runtime, and any
modifications using configure will be lost on program exit.

..

    If you're using ``dynamic settings`` the *configure* method will update the setting value in dynamic storage as well.

Types of settings
-----------------

The simple-settings is prepared to play with the following files types:

-  python modules.
-  cfg files (simple ``key=value`` files).
-  yaml files.
-  json files.
-  toml files.

..

    To simple-settings load settings of yaml files is necessary to install with extra require *yaml*, e.g.: ``pip install simple-settings[yaml]``

..

    For toml files is necessary to install with extras require *toml*, e.g.: ``pip install simple-settings[toml]``


Loading settings from environment variables
-------------------------------------------

simple-settings can load all environment variables, e.g. ``python app.py --settings=.environ`` or only environment variables that start with a certain prefix, e.g. ``python app.py --settings=MYPREFIX_.environ``.


Load multiple settings modules
------------------------------

simple-settings can load more than one setting module without use import
approach, just specify yours settings modules separated by comma. For
example:

.. code:: bash

    $ python app.py --settings=production,amazon,new_relic,PREFIX_.environ

simple-setting will load all settings modules in order that was
specified (``production``-> ``amazon`` -> ``new_relic`` -> ``PREFIX_.environ``) overriding
possibles conflicts.

This also works with *LazySettings* class:

.. code:: python

    from simple_settings import LazySettings


    settings = LazySettings('production', 'amazon', 'new_relic', 'PREFIX_.environ')

You can combine any type of settings (*python modules*, *yaml*, etc.).

Ignored settings
----------------

-  Python modules:

   -  Variables starting with ``_``.

-  Cfg files:

   -  Keys starting with ``#``.

Special Settings
----------------

simple-settings has a list of *special settings* that change how
simple-settings will load settings. This *special settings* are specified using
a ``SIMPLE_SETTINGS`` dict in the settings module.

.. code:: python

    SIMPLE_SETTINGS = {
        'OVERRIDE_BY_ENV': True,
        'CONFIGURE_LOGGING': True,
        'REQUIRED_SETTINGS': ('API_TOKEN', 'DB_USER'),
        'DYNAMIC_SETTINGS': {
            'backend': 'redis',
            'pattern': 'DYNAMIC_*',
            'auto_casting': True,
            'prefix': 'MYAPP_'
        }
    }

Configure logging
~~~~~~~~~~~~~~~~~

If you set the *special setting* ``CONFIGURE_LOGGING`` with ``True``,
*simple-settings* will configure the python logging to you. You just need
to define your logging configuration with
`Python dictConfig format <https://docs.python.org/3.5/library/logging.config.html#configuration-dictionary-schema>`__
and place in ``LOGGING`` setting, e.g.

.. code:: python

    LOGGING = {
        'version': 1,
        'disable_existing_loggers': False,
        'formatters': {
            'default': {
                'format': '%(asctime)s %(levelname)s %(name)s %(message)s'
            },
        },
        'handlers': {
            'logfile': {
                'level': 'DEBUG',
                'class': 'logging.handlers.RotatingFileHandler',
                'filename': 'my_log.log',
                'maxBytes': 50 * 1024 * 1024,
                'backupCount': 10,
                'formatter': 'default'
            },
        },
        'loggers': {
            '': {
                'handlers': ['logfile'],
                'level': 'ERROR'
            },
            'my_project': {
                'level': 'INFO',
                'propagate': True,
            },
        }
    }

To use just get logger with ``logging.getLogger()``, e.g.

.. code:: python

    import logging
    logger = logging.getLogger('my_project')


    logger.info('Hello')

..

    Don't forget, *simple-settings* is lazy and it only configures logging after runs ``setup()`` method or after reads some setting.

Override settings value
~~~~~~~~~~~~~~~~~~~~~~~

You can override the values of your settings module with environment
variables. You just need set the *special setting* ``OVERRIDE_BY_ENV``
with ``True`` as value.

.. code:: bash

    $ export SIMPLE_CONF="simple from env"
    $ python app.py --settings=project_settings
    simple from env

..

    This is not a dynamic behavior, because settings are only overriden at
    *"settings setup"* time; see ``dynamic settings`` for a real dynamic
    behavior.

Required Settings
~~~~~~~~~~~~~~~~~

You can determine a list of mandatory settings, i.e. settings that
require a valid value. For this, set the *special setting*
``REQUIRED_SETTINGS`` to a list (or any iterable) of your required
settings. If any setting in this list has an invalid value (or is not
present in setting file) then a ``ValueError`` is raised with a list of
required settings not satified in the settings file.

Required Not None Settings

You can also determine a list of settings that must have a not none value, i.e. settings that cannot be set as none. For this, set the special setting REQUIRED_NOT_NONE_SETTINGS to a list (or any iterable) of the settings that you require to not be none. If any setting in this list has a value of none, then a ValueError is raised with a list of settings that must be set to not none.

Required Settings Types

You can enforce that settings must have a particular type. For this, set the
*special setting* ``REQUIRED_SETTINGS_TYPES`` to a dictionary with the keys
being the name of the setting and the value being the type of the setting (see
list below for supported values).

If any of these settings has a value that is not of the type specified, or is a
string that cannot be parsed to the type specified, a ``ValueError`` is raised
with a list of settings that are of the wrong type. If there are no errors, the
setting value will be converted into that type. If any of the values are none,
their type is not evaluated.

The supported types are listed below. If you attempt to set a type that is not
one of these types, then a ``ValueError`` will be raised with any unsupported
types.

    - ``"bool"`` - python's native boolean type, True values are ``y``, ``yes``, ``t``, ``true``, ``on`` and ``1``; false values are ``n``, ``no``, ``f``, ``false``, ``off`` and ``0``
    - ``"int"`` - python's native integer type, parsed from a string using ``int(value)``
    - ``"float"`` - python's native float type, parsed from a string using ``float(value)``
    - ``"str"`` - python's native string type, not parsed from a string
    - ``"json.loads"`` - Can be some types resulted of python's ``json.loads(value)`` function (e.g. dict: '{"foo": "bar"} -> {'foo': 'bar'}, int: '1' -> 1, bool: 'true' -> True, list: '[1, 2]' -> [1, 2], etc.)

Dynamic Settings
~~~~~~~~~~~~~~~~

simple-settings has a list of *dynamic settings* mechanisms that change
a value of setting dynamically. If dynamic setting is activate, for all
setting the dynamic reader is called. The current dynamic mechanisms
suported is:

Default Dynamic Settings Configuration
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

For all *dynamic settings* backends *simple-settings* accept this
optional parameters:

-  ``pattern``: if you set some regex pattern the dynamic settings
   reader only get settings that match with this pattern. (Note that the
   pattern will be applied to key as entered, ignoring any configured
   ``prefix`` setting.)
-  ``auto_casting``: if you set this conf to ``True`` (default is
   ``False``) *simple settings* use
   `jsonpickle <https://github.com/jsonpickle/jsonpickle>`__ to encode
   settings value before save in dynamic storage and decode after read
   from dynamic storage. With this bahavior you can use complex types
   (like *dict* and *list*) in dynamic settings.
-  ``prefix``: if you set a prefix this value will be prepended to the
   keys when looked up on the backend. The value is prepended without
   any interpretation, so the key
   ``key="MYKEY" and prefix="my/namespace/"`` would resolve to
   ``key="my/namespace/MYKEY"`` and
   ``key="MYKEY" and prefix="MY_NAMESPACE_"`` would resolve to
   ``key="MY_NAMESPACE_MYKEY"``.

Redis
^^^^^

You can read your settings dynamically in redis if you activate the
``DYNAMIC_SETTINGS`` special setting with ``redis`` backend:

.. code:: python

    SIMPLE_SETTINGS = {
        'DYNAMIC_SETTINGS': {
            'backend': 'redis',
            'host': 'locahost',
            'port': 6379,
        }
    }

..

    for ``redis`` backend ``localhost`` is default value for ``host`` and ``6379`` is the default value for ``port``.

In redis dynamic reader the binary types is automatically decoded.

    To install with redis dependencies use:
    ``pip install simple-settings[redis]``

Consul
^^^^^^

You can read your settings dynamically from a consul server if you
activate the ``DYNAMIC_SETTINGS`` special setting with the ``consul``
backend (uses `consulate <https://github.com/gmr/consulate>`__ library):

.. code:: python

    SIMPLE_SETTINGS = {
        'DYNAMIC_SETTINGS': {
            'backend': 'consul',
            'host': 'locahost',
            'port': 8500,
            'prefix': 'mynamespace/'
        }
    }

..

    for ``consul`` backend ``localhost`` is default value for ``host`` and ``8500`` is the default value for ``port``.

Additional attributes for consul backend: ``datacenter``, ``token``,
``scheme``.

    To install with consul dependencies use:
    ``pip install simple-settings[consul]``

DATABASE
^^^^^^^^

You can read your settings dynamically form a database if you activate
the ``DYNAMIC_SETTINGS`` special setting with the ``database`` backend
(uses `sqlalchemy <http://docs.sqlalchemy.org/>`__ library)

.. code:: python

    SIMPLE_SETTINGS = {
        'DYNAMIC_SETTINGS': {
            'backend': 'database',
            'sqlalchemy.url': 'sqlite:///:memory:',
            ...
        }
    }

..

    To install with database dependencies use: ``pip install simple-settings[database]``


AWS S3
^^^^^^

You can read your settings dynamically form a AWS S3 bucket if you activate
the ``DYNAMIC_SETTINGS`` special setting with the ``s3`` backend
(uses `boto3 <http://boto3.readthedocs.io/en/latest/>`__ library)

.. code:: python

    SIMPLE_SETTINGS = {
        'DYNAMIC_SETTINGS': {
            'backend': 's3',
            'bucket_name': 'simple-settings',
            'region': 'us-east-1'
            ...
        }
    }

..

    To install with s3 dependencies use: ``pip install simple-settings[s3]``


Memcached
^^^^^^^^^

You can read your settings dynamically with memcached if you activate
the ``DYNAMIC_SETTINGS`` special setting with the ``memcached`` backend
(uses `pymemcached <https://pymemcache.readthedocs.io/en/latest/index.html>`__ library)

.. code:: python

    SIMPLE_SETTINGS = {
        'DYNAMIC_SETTINGS': {
            'backend': 'memcached',
            'host': 'localhost',
            'port': 11211
            ...
        }
    }

..

    To install with memcached dependencies use: ``pip install simple-settings[memcached]``


Utils
-----

Settings Stub
~~~~~~~~~~~~~

A simple context manager (and decorator) class useful in tests which is
necessary to change some setting in the safe way.

Context Manager example
^^^^^^^^^^^^^^^^^^^^^^^

.. code:: python

    from simple_settings import settings
    from simple_settings.utils import settings_stub


    with settings_stub(SOME_SETTING='foo'):
        assert settings.SOME_SETTING == 'foo'
    assert settings.SOME_SETTING == 'bar'

Decorator example
^^^^^^^^^^^^^^^^^

.. code:: python

    from simple_settings import settings
    from simple_settings.utils import settings_stub


    @settings_stub(SOME_SETTING='foo')
    def get_some_setting():
        return settings.SOME_SETTING

    assert get_some_setting() == 'foo'
    assert settings.SOME_SETTING == 'bar'


Advanced Usage
--------------

Custom Strategy
~~~~~~~~~~~~~~~

To implement a custom strategy:

.. code:: python

    from simple_settings import settings

    class SettingsCustomStrategy:
        """
        See `/simple_settings/strategies` for sample strategies (e.g. python, json, cfg)
        """

    settings.add_strategy(SettingsCustomStrategy)


Custom Dynamic Settings Reader

You can easily create your own dynamic settings reader. To do that you need to create a class than inherit from simple_settings.dynamic_settings.base.BaseReader and implement _get and _set methods, f.ex:

.. code:: python

from simple_settings.dynamic_settings.base import BaseReader

class Reader(BaseReader):

   def __init__(self, conf):
       super(Reader, self).__init__(conf)
       self._dict = {}

   def _get(self, key):
       return self._dict.get(key)

   def _set(self, key, value):
       self._dict[key] = value

..

To use it, just configure SIMPLE_SETINGS special setting with the full path of the reader, f.ex:

.. code:: python

'SIMPLE_SETTINGS': { 'DYNAMIC_SETTINGS': { 'backend': 'path.of.module.ClassName' } } ..

Any other config of dynamic settings will be pass to reader backend on argument conf

Changelog

[1.0.0] - 2020-09-29

- Drop support to python < 3.6.
- Update dependencies.


[0.19.1] - 2019-10-21

• Load dynamic settings reader with both ways, full class path and module path (assuming the reader class is called Reader)

[0.19.0] - 2019-10-18

- Change import dynamic reader mechanism to using full class path with dot notation
- Update several dependencies
- ``json.loads`` of ``REQUIRED_SETTINGS_TYPES`` now converts and validate lists

[0.18.0] - 2019-07-14

• Fix TypeError on jsonpickle.decode when auto_casting is True and dynamic backend returns None.
• Raise exception containing settings_file information when an error occurs in strategy.load_settings_file call from _load_settings_pipeline.
• If dynamic settings is enabled, query first the dynamic backend before raising an AttributeError.

[0.17.0] - 2019-07-10

- Allow settings to be loaded from environment variables via ``.environ`` or ``PREFIX_.environ``
- Allow ``LazySettings.strategies`` to be easily overridden.
- Using ``strtobool`` from standard library on ``Required Settings Type`` feature.

[0.16.0] - 2019-02-23

• json.loads as new REQUIRED_SETTINGS_TYPES

[0.15.0] - 2019-02-23

- Enforce ordering of special settings being applied
- Dynamic settings behaviors with ``memcached``.
- Fix ``TypeError`` on load settings by YAML file with a relative path

[0.14.0] - 2019-01-31

• Required not none special setting
• Required types special setting and type conversion

[0.13.0] - 2018-03-28

- Dynamic settings behaviors with ``AWS S3``.

[0.12.1] - 2017-10-27

• Fix dynamic settings read behavior to ignore only None values and not zeros values ( #68 <https://github.com/drgarcia1986/simple-settings/issues/68>__)

[0.12.0] - 2017-03-07

-  Load settings from *toml* files.

[0.11.0] - 2017-02-17

• Autoconfigure python logging with CONFIGURE_LOGGING special setting.

[0.10.0] - 2016-10-28

-  Support configuring dynamic backends with an optional *prefix*.

[0.9.1] - 2016-09-15
~~~~~~~~~~~~~~~~~~~~

-  ``configure`` method now works even called before the LazySettings
   setup.

[0.9.0] - 2016-08-12
~~~~~~~~~~~~~~~~~~~~

-  ``configure`` method now update settings in dynamic settings.
-  On get setting value in dynamic setting update local settings with
   this value.
-  Auto casting value in dynamic storage to using complex types.

[0.8.1] - 2016-06-04
~~~~~~~~~~~~~~~~~~~~

-  Fix instalation with ``database`` extra requires.

[0.8.0] - 2016-06-04
~~~~~~~~~~~~~~~~~~~~

-  Better ``ImportError`` message if using a dynamic reader without your
   lib dependencies.
-  Refactor in Settings Stub.
-  Dynamic settings behaviors with ``SQLAlchemy`` (``database``
   backend).
-  Load settings of *json* files.

[0.7.0] - 2016-06-02
~~~~~~~~~~~~~~~~~~~~

-  Nice python *REPR* for *LazySettings* objects.
-  Dynamic settings behaviors with ``Redis``.
-  Dynamic settings behaviors with ``Consul``.
-  Generate package with python wheel.

[0.6.0] - 2016-05-17
~~~~~~~~~~~~~~~~~~~~

-  Some refactors.
-  Determine settings files and modules directly in LazySettings object
   (to avoid use env or command line argument).
-  ``configure`` method to update settings.
-  Use ``safe_load`` instead ``load`` in yaml strategy.

[0.5.0] - 2016-02-03
~~~~~~~~~~~~~~~~~~~~

-  Some refactors.
-  Load settings of *yaml* files.
-  New ``SIMPLE_SETTINGS`` environment variable.
-  New ``--simple-settings`` command line arg.

[0.4.0] - 2016-01-03
~~~~~~~~~~~~~~~~~~~~

-  Lazy settings load.

[0.3.1] - 2015-07-23
~~~~~~~~~~~~~~~~~~~~

-  Avoid to load python modules (as settings) in python files (with
   this, fix ``deepcopy`` bug in ``as_dict()`` method).

[0.3.0] - 2015-07-19
~~~~~~~~~~~~~~~~~~~~

-  Deepcopy in ``as_dict`` method to anticipate unexpected changes.
-  Special Settings Behaviors.

   -  Override settings values by environment.
   -  Required settings validation.

-  Remove default behavior of override settings values by environment
   (now it's a special settings).
-  Settings Stub (useful for tests)
-  Change bahavior of settings ``__getattr__`` (before may raise
   ``KeyError`` if simple-settings do not locate the setting, now raise
   ``AttributeError``)

[0.2.0] - 2015-06-19
~~~~~~~~~~~~~~~~~~~~

-  Load multiple settings separated by comma (like a pipeline).
-  Load settings of *cfg* files.
-  Filter python module attributes to read only user settings.

[0.1.1] - 2015-05-19
~~~~~~~~~~~~~~~~~~~~

-  Fix parser\_args error if using simple-settings with others command
   line arguments.

[0.1.0] - 2015-05-14
~~~~~~~~~~~~~~~~~~~~

-  First release.