Register Reference Guide

Appregister comes with two different build in Registries, Register and NamedRegister.

Register

The Register class is the simplest registry, for storing a set of unique subclasses. A Register can be defined like so:

from appregister import Register

class QuestionRegister(Register):
    base = 'myproject.Question'
    discovermodule = 'questions'

questions = QuestionRegister()

Reference

The Register class implements the Sized and Iterable ABC’s from the collections module and adds the following methods.

all

Accepts no arguements and returns a set containing all of the registered subclases.

autodiscover

Accepts no arguements and checks each of the INSTALLED_APPS for a module with the same named as discovermodule to find any registered subclasses.

clear

Accepts no arguements and resets the registry and removes any previously registered classes.

regsiter

Accepts a class object that must extend base. This class is added to the registry.

The exception appregister.base.AlreadyRegistered is raised if the class has already been registered.

The exception appregister.base.InvalidOperation is raised if the class is not a subclass of base.

unregister

Accepts a class, and removes it from the registry. If the class is not registered a KeyError is raised.

Usage Example

The following example assumes that the QuestionRegister that is defined above is added to the file registry.py in your myproject package:

from myproject import registry

@registry.questions.register
class MultipleChoiceQuestion(Question):
    pass
    # ...

# If you are using a Python version older than 2.6, rather than using the
# function as a class based decorator you will nee to use

Class MultipleChoiceQuestion(Question):
    pass
    # ...

registry.questions.registered(MultipleChoiceQuestion)

NamedRegister

The named register includes all of the functionality of the Register class but extended to require a name (or key) for each registered subclass. The NamedRegister also doesn’t require registered classes to be unique, other than a key can only be registered once.

The NamedRegister does not require any further steps than Register when defining your class register, so it can be defined like so:

from appregister import NamedRegister

class NamedQuestionRegister(NamedRegister):
    base = 'myproject.Question'
    discovermodule = 'questions'

named_questions = NamedQuestionRegister()

Reference

The Register class implements the Mapping ABC from the collections module, so it can be used like a dict and it also adds/changes the following methods.

all

Accepts no arguements and returns a dict containing all of the registered subclases.

regsiter

Accepts a key and a class object that must extend base. This class is added to the registry under the given key.

The exception appregister.base.AlreadyRegistered is raised if the key has already been registered.

The exception appregister.base.InvalidOperation is raised if the class is not a subclass of base.

unregister

Accepts a key, and removes it from the registry. If the key is not registered a KeyError is raised.

names

Accepts no arguements and returns a list of all the registered names.

Usage Example

The following example like with the Register example assumes that the NamedQuestionRegister is added to the file registry.py in your myproject package:

from myproject import registry

@registry.named_questions.register("Multiple Choice")
class MultipleChoiceQuestion(Question):
    pass
    # ...

# If you are using a Python version older than 2.6, rather than using the
# function as a class based decorator you will nee to use

Class MultipleChoiceQuestion(Question):
    pass
    # ...

registry.questions.registered("Multiple Choice", MultipleChoiceQuestion)