Good Handlers

Method and function handlers that implement common behaviors without writing the entire function

Handlers

Handlers are objects that act as methods in a class. They are good for configurable, predefined functions which will otherwise be redundant to implement. Handler functionality is implemented in standard python's __call__ method, which otherwise treats the handler like a function.

from good_handlers import InstanceHandler

class MyHandler(InstanceHandler):
    def __init__(self, scale):
        self._scale = scale

    def __call__(self, instance, arg1, arg2):
        instance.result = scale*(arg1+arg2)

The class InstanceHandler binds to an instance. This requires the extra instance parameter, which will become the bound instance of the handler

from good_handlers import InstanceHandler

class MyHandler(InstanceHandler):
    def __init__(self, scale, save='last_result'):
        self._scale = scale
        self._save = save

    def __call__(self, instance, arg1, arg2):
        setattr(instance, self._save, scale*(arg1+arg2))

class MyClass:
    def __init__(self):
        self.last_result = None

    handler = MyHandler(3)

The class ClassHandler binds to a class and passes the bound class to the extra klass parameter.

from good_handlers import ClassHandler

class DefaultAgePersonMaker(ClassHandler):
    def __init__(self, defage):
        self._defage = defage

    def __call__(self, klass, name):
        return klass(name=name, age=self._defage)

class Person:
    make_twenty_year_old = DefaultAgePersonMaker(20)

    def __init__(self, name, age):
        self._name = name
        self._age = age

jim = Person.make_twenty_year_old('Jim Shim') # Makes Person('Jim Shim', 20)

Init Handlers

A special case of redundant programming is the __init__ method. Often times, the __init__ is only used to set a series of member variables. Thus, they will often contain a lot of boilerplate code. The Good Library offers a few __init__ handlers, which simplify creating __init__ methods. NamedInitHandler sets member variables according to a tuple of names provided in the names parameter.

from good_handlers.init import NameInitHandler

class Person:
    __init__ = NameInitHandler(
        names=('name', 'age', 'apparel', 'thoughts')
    )

Default values for these can be provided as a dict in the defaults parameter.

from good_handlers.init import NameInitHandler

class Person:
    __init__ = NameInitHandler(
        names=('name', 'age', 'apparel', 'thoughts'),
        defaults={
            'apparel': 'Pajamas',
            'thoughts': 'Nothing at the moment...'
        }
    )

UnderscoreInitHandler is a type of NamedInitHandler that appends an underscore _ to each name before setting it in the instance. DunderInitHandler adds a dunder, or a double-underscore __ before each name

String Handlers

Another case of redundant programming is string representations. The Good Library provides ValueStringHandler, which prints the object name and the values of the given keys to show, and KeyValueStringHandler, which is like ValueStringHandler, but displays key=value pairs instead of just values

from good_handlers.string import ValueStringHandler, KeyValueStringHandler

class Person1:
    """
    Docstring for Person
    """
    def __init__(self, name, age):
        """
        Initializes instance
        """
        self.name = name
        self.age = age

    __repr__ = ValueStringHandler(('name', 'age'))

class Person2:
    """
    Docstring for Person2
    """
    def __init__(self, name, age):
        """
        Initializes instance
        """
        self.name = name
        self.age = age

    __repr__ = KeyValueStringHandler(('name', 'age'))

john1 = Person1('John Numberone', 21)
john2 = Person2('John Numbertwo', 28)

print(john1) # prints 'Person1(\'John Numberone\', 21)'
print(john2) # prints 'Person2(name=\'John Numbertwo\', age=28)'