Registry

essentials includes a base class for classes that can be instantiated from configuration dictionaries. This is to handle configurable objects whose concrete type is not known before hand.

from essentials.registry import Registry


class Rule(Registry):
    pass

class OneRule(Rule):
    def __init__(self, a, b):
        self.a = a
        self.b = b

class TwoRule(Rule):
    def __init__(self, c, d):
        self.c = c
        self.d = d

x = Rule.from_configuration({
    'type': 'one',
    'a': 10,
    'b': 20
})

assert isinstance(x, OneRule)
assert x.a == 10
assert x.b == 20

x = Rule.from_configuration({
    'type': 'two',
    'c': 100,
    'd': 200
})

assert isinstance(x, TwoRule)
assert x.c == 100
assert x.d == 200

Or, by explicit type name:

# for example, imagine a class to store some output, that can be configured to use different implementations

class OutputStore(Registry):
    pass

class FileSystemOutputStore(OutputStore):

    type_name = 'fs'

    def __init__(self, file_name):
        self.file_name = file_name


class MySqlOutputStore(OutputStore):
    
    type_name = 'mysql'

    def __init__(self, connection_string):
        self.connection_string = connection_string