Ned Batchelder <n...@nedbatchelder.com> writes: > On 1/31/14 2:33 PM, Mark Lawrence wrote: > > From http://docs.python.org/3/reference/datamodel.html#object.__init__ > > […] > > Should the wording of the above be changed to clearly reflect that > > we have an initialiser here and that __new__ is the constructor? > > I'm torn about that. The fact is, that for 95% of the reasons you want > to say "constructor", the thing you're describing is __init__.
I assume the “95%” figure is made up. Whose wants are you divining, here? > Most classes have __init__, only very very few have __new__. Yes, this is true, and I agree it is a major factor in the confusion: the term “constructor” is commonly encountered in discussion of classes, and in Python, the method “__init__” is commonly encountered. It is a natural mistake to think Python names its constructor “__init__”, since most classes don't define “__new__”. > The sense that __new__ is the constructor is the one borrowed from C++ > and Java: you don't have an instance of your type until the > constructor has returned. This is why __init__ is not a constructor: > the self passed into __init__ is already an object of your class. A more salient reason, I think, is that “constructor” entails that the function will return the instance. This is another important reason why “__init__” is not a constructor: it does not return the instance. > But that distinction isn't useful in most programs. The thing most > people mean by "constructor" is "the method that gets invoked right at > the beginning of the object's lifetime, where you can add code to > initialize it properly." That describes __init__. Here we disagree. I think the meaning “… and that returns the new instance” is entailed in the meaning of “constructor”. > Why can't we call __init__ the constructor and __new__ the allocator? Because those terms already have meanings, and “__new__” fits the meaning of “constructor” better. -- \ “This world in arms is not spending money alone. It is spending | `\ the sweat of its laborers, the genius of its scientists, the | _o__) hopes of its children.” —Dwight Eisenhower, 1953-04-16 | Ben Finney -- https://mail.python.org/mailman/listinfo/python-list
