How to implement setitem to set attributes of a class?

Question

my classes

class Base:

    #has no attributes of its own



    def __init__(self, params):

        for key in params:

            if hasattr(self, key):

                self[key] = params[key]



    def __setitem__(self, key, value):

        self[key] = value







class Child(Base):

    prop1 = None

    prop2 = None

This however, goes into endless recursion as

self[key] = value

recursively calls

self.__setitem__

My goal is to be able to pass a a dictionary into a

Child()

constructor like this

params = dict(

    prop1 = "one",

    prop2 = "two"

)

c = Child(params)



c.prop1     #"one"

c.prop2     #"two"

There are many different classes like Child but with different fields.

params

is a dict from a json blob. I want to use

Base

as a generic populator for the different classes like

Child

I have seen methods that use an internal

dict

to accomplish what I am asking but it is my understand (I am brand new to Python) that this would prevent accessing the methods via dot notation (which I would rather avoid).

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Answer 1

Just update the __dict__ of the instance in your __init__:

class Base:
    def __init__(self, params):
        for key in params:
            if hasattr(type(self), key):
                self.__dict__[key] = params[key]

Then:

class Child(Base):
    field1 = None
    field2 = None

c = Child(dict(field1="one", field2="two", field3="three"))

print(c.field1)     # "one"
print(c.field2)     # "two"
print(c.field3)     # => attr error

Grandchildren will behave:

class GrandChild(Child):
    field3 = None

gc = GrandChild(dict(field1="one", field2="two", field3="three"))

print(gc.field1)     # "one"
print(gc.field2)     # "two"
print(gc.field3)     # "three"

How to implement __setitem__ to set attributes of a class?

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How to implement setitem to set attributes of a class?