CODEWITHSUNDEEP
pythonobjectbuilt-in
abcd
abcd

Reputation: 10761

Understanding Python's `property` and `__init__`

Consider the following class:

class HotDog():

    def __init__(self):
        self.v_th = 10

    def _new_property(obj_hierarchy, attr_name):
        def set(self, value):
            obj = reduce(getattr, [self] + obj_hierarchy.split('.'))
            setattr(obj, attr_name, value)
        def get(self):
            obj = reduce(getattr, [self] + obj_hierarchy.split('.'))
            return getattr(obj, attr_name)
        return property(fset=set, fget=get)

    x.vthresh = 77

    v_th = _new_property('x', 'vthresh')

If I were to create an instance of this class -- say, x = HotDog() -- I would find that x.v_th == 10. Why is this the case? It seems to me that the value should be set to 10 initially, but then overwritten when self.v_th is rededfined to be _new_property('x', 'vthresh'). Is the code in __init__ executed after this other code when x is initialized?

Upvotes: 1

Views: 33

Answers (1)

Ignacio Vazquez-Abrams
Ignacio Vazquez-Abrams

Reputation: 798814

All code at class scope is executed when the class is created. The __init__() method is called when the object is created. Therefore all class scope code is run before the __init__() method is.

Upvotes: 3

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