On Mon, Dec 26, 2011 at 10:48 PM, Fredrik Tolf <fred...@dolda2000.com> wrote: > I'm also a bit confused about __new__. I'd very much appreciate it if > someone could explain the following aspects of it: > > * The manual (<http://docs.python.org/reference/datamodel.html>) says > that __new__ is "a static method (special-cased so you need not declare > it as such)". What does "special-cased" mean? Apparently, for > instance, in OP's case, Python did not automatically detect that it > should not be bound as a method.
It apparently has to do with the class creation. For the special-casing to happen, the __new__ method has to be present when the class is created. If it is, then it automatically gets wrapped in a staticmethod. In the OP's case, he was adding the __new__ method after class creation, so the wrapping did not happen automatically. Compare: >>> def my_new(cls): return object.__new__(cls) ... >>> class Foo(object): ... __new__ = my_new ... >>> class Bar(object): pass ... >>> Bar.__new__ = my_new >>> Foo.__dict__['__new__'] <staticmethod object at 0x0237D6F0> >>> Bar.__dict__['__new__'] <function my_new at 0x02381430> > * Is there any part of the manual that explains, holistically, the > greater context of object instantiation into which __new__ fits? I can > only find small parts of it spread around the documentation for __new__ > and __init__, but no complete explanation of it. There are several > things I'm wondering about, like what it means to call a type object at > all; I don't know of anything that organizes it that way specifically, but I believe the Data Model reference pretty much covers what you're looking for. From the type hierarchy, under "Callable Types": http://docs.python.org/reference/datamodel.html#the-standard-type-hierarchy """ Class Types Class types, or “new-style classes,” are callable. These objects normally act as factories for new instances of themselves, but variations are possible for class types that override __new__(). The arguments of the call are passed to __new__() and, in the typical case, to __init__() to initialize the new instance. """ AFAIK, that's pretty much it. When a type is called, __new__ is called to create the new instance, and then __init__ is called to initialize it (if __new__ returned an instance of the type). > how methods, properties and the like are bound; When they're accessed, using the descriptor protocol, not as part of the instantiation process. See: http://docs.python.org/reference/datamodel.html#invoking-descriptors > how pickle can > instantiate a class without calling __init__; By calling the __new__ method directly instead of calling the type: http://docs.python.org/library/pickle.html#object.__getnewargs__ > when and whether __dict__ > is created and a couple of other things. Under the hood as part of the object creation process, unless the class uses __slots__. -- http://mail.python.org/mailman/listinfo/python-list
