__init__ not a "constructor" ?

Tim Hammerquist tim at vegeta.ath.cx
Tue Aug 14 02:11:56 CEST 2001


Me parece que Kirby Urner <urner at alumni.princeton.edu> dijo:
> 
> I notice the author of the Dive Into Python tutorial cautions
> that __init__ is not trully a class constructor, as by the time
> it's invoked, an instance already exists (hence the argument
> 'self', hence the fact that classes don't need an __init__
> method).

I'm not sure what the author means, but:

class A:
    def __init__(self, *args):
        # do stuff

... is roughly analogous to C++'s constructors, if you don't count C++'s
implicit passing of the object.

...both of which are drastically different from Perl's OO constructor
syntax, requiring a constuctor of any name to "bless" this object (a
string ref, an array ref, a hash ref, a filehandle ref) into the given
"class" (ie, package name).  This is no doubt convoluted, but simplifies
certain processes, such as a wrapper object for an array;
$obj->[0] then refers directly to the first element, rather than having
to call, say, $obj->return_element(0). OTOH, doing this in Python
requires a lot of extra __*__ methods in the class.  You can see there
are dozens of arguments this way, but I much prefer OO in Python. <wink>

> I'm wondering if it's therefore considered faux pax to refer to
> the constructor of a Python user-defined class, meaning __init__,
> or if there's some tacit liberalizing of "constructor" (it's meaning)
> going on, such that this usage is acceptable.

For as much as OO is talked about, there are sooooooo many different
words for the same thing.

    object == instance
    data member == attribute ( ~ instance variable )
    inheritance == derivation
    interface == behavior
    interface (Java) == 'mix-in' class
    method call == message
    instantiation == creation
    super class == base class
    * and many, many more *

As such, words are bound to have their meanings confused; but I don't
think people ever agreed on terminology in the first place. <wink>

IMNERHO[1], the purpose of OO is abstraction of data to make it
easier to use and extend.  If you're accomplishing this, it's OO.

IMNERHO = In My Never Even Remotely Humble Opinion

<dons flame-proof armor> <wink!>

HTH
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