Andrej Viktorovich <viktorovichand...@gmail.com> writes:
> For my understanding both - __init__() and __new__() works like
> constructors.
Not true, they work quite differently and have very different jobs.
> And __new__() looks is closer to constructor. __init__() is more for
> variable initialization.
That's right.
The class's ‘__new__’ method – note that it is a class method, it takes
the class as its first parameter – is the constructor. It constructs a
new instance, and its return value is that instance.
The instance's ‘__init__’ method – note that it is an instance method,
it takes the already-constructed instance as its first parameter – is
the initialiser. It acts on the existing instance, setting it up for its
initial state, and its return value is None.
> Why I can't just initialize in __init__() ?
You can. You should.
What leads you to believe otherwise?
> class ExampleClass(object):
> def __new__(cls,value):
> print("creating new instance with val %s" % (value,) )
> instance = super(ExampleClass,cls).__new__(cls)
> return instance
> def __init__(self, value):
> print("Initialising instance... with val %s" % (value,))
> self.payload = value
Yes, those look fine (but for new code you should be using Python 3,
which allows you to write ‘instance = super().__new__()’).
--
\ “Our urge to trust our senses overpowers what our measuring |
`\ devices tell us about the actual nature of reality.” —Ann |
_o__) Druyan, _Cosmos_, 2014 |
Ben Finney
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