Usage¶
Declaring your settings¶
To declare your application settings, create a settings class inheriting from
appsettings.AppSettings
:
import appsettings
class MySettings(appsettings.AppSettings):
boolean_setting = appsettings.BooleanSetting(default=False)
required_setting = appsettings.StringSetting(required=True)
named_setting = appsettings.IntegerSetting(name='integer_setting')
prefixed_setting = appsettings.ListSetting(prefix='my_app_')
nested_setting = appsettings.NestedSetting(settings=dict(
foo_setting=appsettings.BooleanSetting(prefix='inner_'),
))
class Meta:
setting_prefix = 'app_'
In this example, we declared six different settings in our class:
boolean_setting
, required_setting
, named_setting
,
prefixed_setting
, nested_setting
and foo_setting
(which is inner setting of nested_setting
).
The corresponding variable names in a Django project’s settings file will be:
boolean_setting
:APP_BOOLEAN_SETTING
, because no name was given.required_setting
:APP_REQUIRED_SETTING
, because no name was given.named_setting
:APP_INTEGER_SETTING
, because a name was given.prefixed_setting
:MY_APP_PREFIXED_SETTING
, because we overrode the class prefix.nested_setting
:APP_NESTED_SETTING
, because no name was given. The corresponding value is a dictionary.foo_setting
:APP_NESTED_SETTING['INNER_FOO_SETTING']
, becausefoo_setting
is inner setting ofnested_setting
and prefix was given.
We could as well give both name and prefix to customize entirely the corresponding variable name in the settings file.
Using a callable as default value¶
Sometimes you may want to pass a callable as a default value. To ensure that the
callable is called, or to prevent it, use the call_default
parameter:
from datetime import datetime
import appsettings
class MySettings(appsettings.AppSettings):
# expect a datetime value, allow calling
first_access = appsettings.Setting(default=datetime.now, call_default=True)
# expect a function returning current time, prevent calling
now_function = appsettings.Setting(default=datetime.now, call_default=False)
call_default
is True by default on every setting class except ObjectSetting
.
Important
Note that call_default
is only used when the related setting is missing
from the project settings!
Checking the settings¶
The best place to check your application settings is in your application configuration class:
import django
import appsettings
class AppSettings(appsettings.AppSettings):
string_list = appsettings.ListSetting(item_type=str,
empty=False,
required=True,
max_length=4)
class Meta:
setting_prefix = 'my_app_'
class AppConfig(django.apps.AppConfig):
name = 'my_app'
verbose_name = 'My Application'
def ready(self):
# check every settings at startup, raise one exception
# with all errors as one message
AppSettings.check()
In the above example, if MY_APP_STRING_LIST
is not defined, or if it is not
a list object, or if it’s empty, or if it has more than 4 elements,
AppSettings.check()
will raise a ImproperlyConfigured
exception.
If you had more settings declared in your settings class, then the
ImproperlyConfigured
exception would be raised with a message being a
concatenation of the first exception for each setting checked.
You can also check each setting individually, for example:
for setting in AppSettings.settings.values():
setting.check()
If the setting’s value is invalid, it will raise an exception
(usually ValueError
).
Using the settings in your code¶
Once your settings class is ready, you will be able to instantiate it to benefit from its simplicity of use and its caching feature:
# let say you declared your Settings class in apps.py
from .apps import Settings
settings = Settings()
print(settings.string_list[0])
print(settings.now_function())
print(settings.first_access.day)
Nested settings¶
If you want to define nested settings, such as django setting DATABASES
,
you may utilize NestedSetting
. Those are a little bit complicated, so
we’ll explain them using simple example:
import appsettings
class MySettings(appsettings.AppSettings):
api = appsettings.NestedSetting(
prefix='our_'
settings=dict(
server=appsettings.StringSetting(prefix='my_', required=True),
port=appsettings.IntegerSetting(default=80, name='magic'),
)
)
class Meta:
setting_prefix = 'app_'
Attributes of the parent does not affect the attributes of the child and vice versa. Child settings ignore the metaclass prefix. Lets see, what happens with different configurations:
Empty configuration would be valid, because
api
setting is not required. In this case,api
default value would be used, which is empty dictionary.Configuration
OUR_API={}
would be invalid, because required itemMY_SERVER
representing subsettingserver
is ommited.Configuration
OUR_API={'MY_SERVER': 'localhost', 'MAGIC': 42}
would be valid:settings = MySettings() print(settings.api) # {'server': 'localhost', 'port': 80} print(setting.api['server']) # 'localhost' print(setting.api['port']) # 42
As you can see, value of nested setting is represented as a dictionary with values of all the subsettings included. If you define other items in the dictionary corresponding to nested setting, those other items are ignored.
Testing the settings¶
When you instantiate your settings class with settings = Settings()
,
the invalidate_cache
method of the instance is automatically connected
to the setting_changed
signal sent by Django. It means that you can test
different values for your settings without worrying about invalidating the
cache each time.
from django.test import SimpleTestCase, override_settings
from my_app.apps import Settings
class MainTestCase(TestCase):
def setUp(self):
self.settings = Settings()
def test_some_settings(self):
# first fetch
assert self.settings.string_list[0] == 'hello'
# django will send setting_changed signal, cache will be cleaned
with override_settings(MY_APP_STRING_LIST=['hello world!']):
assert len(self.settings.string_list) == 1
# signal sent again
with override_settings(MY_APP_STRING_LIST=['good morning', 'world', '!']):
assert len(self.settings.string_list) == 3
# signal is also sent when with clause ends
assert self.settings.string_list[0] == 'hello'
# it works the same way with decorator
@override_settings(MY_APP_STRING_LIST=['bye'])
def test_string_list(self):
assert 'bye' in self.settings.string_list
Customize setting validation¶
Note
New in version 0.4.
You may need to customize the setting validation.
Individual Settings
use validation similar to Django form fields.
The easiest way is to pass additional validators when defining a setting.
import appsettings
from django.core.validators import EmailValidator
setting = appsettings.StringSetting(validators=(EmailValidator(), ))
A more robust method is to create a subclass and define a default_validators
.
import appsettings
from django.core.validators import EmailValidator
class EmailSetting(StringSetting):
default_validators = (EmailValidator(), )
The finest-grained customization can be obtained by overriding the validate()
method.
import re
import appsettings
class RegexSetting(appsettings.Setting):
def validate(self, value):
re_type = type(re.compile(r'^$'))
if not isinstance(value, (re_type, str)):
# Raise ValidationError
raise ValidationError('%(value)s is not a string or a compiled regex (use re.compile)',
params={'value': value})
setting = RegexSetting()
Writing your own type checker¶
Warning
Checkers are deprecated, use validators instead.
The third way to customize how the setting is checked is to create
a new TypeChecker
class:
import re
import appsettings
# option 1: passing a specific base_type (can be a tuple with several types)
class RegexTypeChecker1(appsettings.TypeChecker):
def __init__(self):
re_type = type(re.compile(r'^$'))
super(BooleanTypeChecker, self).__init__(base_type=(str, re_type))
setting1 = appsettings.Setting(checker=RegexTypeChecker1())
# option 2: completely overriding the __call__ method
class RegexTypeChecker2(appsettings.TypeChecker):
def __call__(self, name, value):
re_type = type(re.compile(r'^$'))
if not isinstance(value, (re_type, str)):
# raise whatever exception
raise ValueError('%s must be a a string or a compiled regex '
'(use re.compile)' % name)
setting2 = appsettings.Setting(checker=RegexTypeChecker2())
# option 3: combining both type checker and setting class
class RegexSetting(appsettings.Setting):
def __init__(
self, name='', default=re.compile(r'^$'), required=False,
prefix='', call_default=True, transform_default=False):
super(RegexSetting, self).__init__(
name=name, default=default, required=required, prefix=prefix,
call_default=call_default, transform_default=transform_default,
checker=RegexTypeChecker1())
setting3 = RegexSetting()
Extending type checker and setting classes¶
Warning
Checkers are deprecated, use validators instead.
In the previous example, we combined our own type checker to our own setting class. But we can extend it furthermore by adding parameters to the type checker, or by inheriting from previous type checkers.
from datetime import datetime
import re
import appsettings
class DateTimeTupleTypeChecker(appsettings.TupleTypeChecker):
def __init__(
self, min_length=None, max_length=None, empty=True,
maximum=None):
# here we restrict the parent TupleTypeChecker parameters
# by hard-coding item_type=datetime
super(DateTimeTupleTypeChecker, self).__init__(
item_type=datetime, min_length=min_length,
max_length=max_length, empty=empty)
# and here we add our custom parameters
self.maximum = maximum
# now we are able to extend the check
def __call__(self, name, value):
super(DateTimeTupleTypeChecker, self).__call__(name, value)
if isinstance(self.maximum, datetime):
for i, item in enumerate(value):
if item > self.maximum:
raise ValueError(
'item %d (%s) in setting %s '
'is above maximum %s' % (
i, item, name, self.maximum))
class DateTimeTupleSetting(appsettings.Setting):
def __init__(
self, name='', default=lambda: tuple(), prefix='',
required=False, call_default=True, transform_default=False,
**checker_kwargs):
# we simply hook our type checker into our setting class
super(DateTimeTupleSetting, self).__init__(
name=name, default=default, required=required, prefix=prefix,
call_default=call_default, transform_default=transform_default,
checker=DateTimeTupleTypeChecker(**checker_kwargs))
setting = DateTimeTupleSetting(
name='dates_to_remember', default=lambda: (datetime.now(), ),
min_length=1, maximum=datetime(year=2030, month=1, day=1)
# and the related setting would be
DATES_TO_REMEMBER = (
datetime(year=2017, month=11, day=30), # the day I wrote this line
)
Transforming setting values¶
You may want your setting to be less strict about types, but make sure it always return the same type of object. This is what the transform method is here for:
import re
import appsettings
# our type checker
class RegexTypeChecker(appsettings.TypeChecker):
def __init__(self, **kwargs):
re_type = type(re.compile(r'^$'))
# allow both str and re_type types
super(BooleanTypeChecker, self).__init__(base_type=(str, re_type))
# our setting class
class RegexSetting(appsettings.Setting):
def __init__(
self, name='', default=re.compile(r'^$'), required=False,
prefix='', call_default=True, transform_default=False,
**checker_kwargs):
super(RegexSetting, self).__init__(
name=name, default=default, required=required, prefix=prefix,
call_default=call_default, transform_default=transform_default,
checker=RegexTypeChecker(**checker_kwargs))
def transform(self, value):
# ensure it always returns a compiled regex
if isinstance(value, str):
value = re.compile(value)
return value
setting = RegexSetting()
You can also control whether the default value has to be transformed or not
with the transform_default
parameter. Using the above example, you could
then instantiate your setting like this:
setting = RegexSetting(default=r'^my (regular)? expression$',
transform_default=True)
You can as well combine call_default
and transform_default
:
def regex_string_generator():
return r'^my (regular)? expression$'
setting = RegexSetting(default=regex_string_generator,
call_default=True,
transform_default=True)
Important
Transformation is always done after calling the default value.