Accessors in Python (getters and setters)

[mystilleef]

Bruno Desthuilliers wrote:
> mystilleef wrote:
> > Bruno Desthuilliers wrote:
> >
> >>mystilleef wrote:
> >>
> >>>Bruno Desthuilliers wrote:
> >>>
> >>>
> >>>>mystilleef wrote:
> >>
> >>(snip)
> >>
> >>>>>>>Of course using setters for the sake of just using them is pointless.
> >>>>>>
> >>>>>>Indeed.
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>>>The reason to use them is if pre-conditions or post-conditions need to
> >>>>>>>be met. Or to control access to an objects states.
> >>>>>>
> >>>>>>Then why advocate *systematic* use of them ?
> >>>>>>
> >>>>>>(snip)
> >>>>>
> >>>>>I never advocated anything.
> >>>>
> >>>>You advocated
> >>>>"""
> >>>>1). Make all attributes of a class private/protected .
> >>>>2). If a "non-callable" attribute is going to be used outside a class,
> >>>>think about making it a property and name the property well, because
> >>>>you never know...
> >>>>"""
> >>>>
> >>>
> >>>
> >>>You use accessors when you need to control access to a data attribute.
> >>
> >>Indeed. And when you don't need too ? (the second 'o' is not a typo)
> >>
> >
> >
> > You make the attribute private/protected.
>
> doh :(
>
> Let's talk about psychorigid mindset...
>

Thanks, I'm insane.

> >
> >>>That's not advocacy, that's common sense.
> >>
> >>I'm afraid we don't use the same definition of "common sense". Writing
> >>useless code is not part of my definition of "common sense".
> >>
> >>(snip)
> >>
> >>>>>I agree. And I already told you I think in terms of state and behavior
> >>>>>and not language dependent semantics.
> >>>>
> >>>>Then why do you advise "(making) all attributes of a class
> >>>>private/protected" and systematically using properties ?
> >>>>
> >>>
> >>>
> >>>Because you don't want third parties illegimately tampering with an
> >>>object's internal data and thus crashing your system?
> >>
> >>Let's try again...
> >>
> >>point 1 : there's *no* language-inforced access restriction in Python.
> >>Just a *convention*.
> >>
> >
> >
> > Huh? What are properties for then?
>
> To allow attribute syntax when you really have computation behind. Which
>  1/ let you start with the simplest case (a simple attribute) and change
> your mind latter
> 2/ offer the possibility to use an attribute syntax (instead of a method
> call syntax) when it seems more natural.
>

Right, and what I'm I trying to do again?

> >
> >>point 2 : so anyone *can* "illegimately tampering with an object's
> >>internal data" at will.
> >>
> >
> > And this is robust how?
> >
>
> You can do just the same in Java or C++.
>

OMG!

> >>point 3 : anyway it's not *my* system that will then crash - but the
> >>system of the one who "illegimately" played with my package's objects
> >>internals. And as far as I'm concerned, it's none of my problem - they
> >>were marked as implementation, so anyone playing with them is on it's
> >>own. FWIW, I suspect that if someone want to muck with implementation,
> >>he certainly has a good legitimate reason to do so, and will do her best
> >>to not break anything. Else he's a complete idiot and there's no cure
> >>for this.
> >>
> >
> >
> > You can't be serious. Please tell me you are joking.
>
> I'm deadly serious and definitively not joking. There's no cure for
> idiocy, and there's definitively nothing like an idiot-proof system.
>

Sure, but calling users idiots for as result of your laziness or poor
design or lack of robustness is equally idiotic.

> >
> >>point 4 : since we have computed attributes, turning a "public data
> >>attribute" (to use your idiom) into a "private/protected data attribute
> >>with accessors" *without breaking the interface* is not even a non-brainer.
> >>
> >>Now, please, can you explain the difference between :
> >>
> >>class Complicated(object):
> >>  def __init__(self, data):
> >>    self.data = data
> >>  def _get_data(self):
> >>    return self._data
> >>  def _set_data(self, data):
> >>    self._data = data
> >>
> >>and
> >>
> >>class Pragmatic(object):
> >>  def __init__(self, data)
> >>    self.data = data
> >>
> >>
> >>and find any *valid* reason to use the first solution instead of the
> >>second ? ('that's what the book says' not being a valid reason).
> >>
> >
> >
> > I don't know it's your code not mine.
>
> IOW : you're unable to find any valid reason to use the second solution
> instead of the first (of course : there's none), but refuse to admit it.
>

Hey, I didn't write that code. You did! You deal with it. My input on
__your__ code at this point is irrelevant.

> >
> > class Robust(object):
> >
> > 	def __init__(self):
> > 		# Arbitrarily changing this state to False will crash app or will
> > 		# corrupt the whole event system.
> > 		self.__is_active = True
> >
> > 	def get_is_active(self):
> > 		return self.__is_active
> >
> > 	buffer_is_active = property(get_is_active, doc="True if buffer is
> > editable")
> >
> > 	def monitor_events(self):
> > 		# Only methods of this class can change __is_active.
> > 		# Add code to change __is_active here.
> > 		return
>
> Yuck.
>
> > See! I'm controlling access.
>
> You are not controlling *anything*
>
> r = Robust()
> r._Robust__is_active = True
>

*sighs*

You keep coming up with these unrealistic and impractically delusional
theories to make yourself feel happy. Sure Python lets your do that,
but that's an implementation detail almost all Python developers could
give a damn about. How many times do I have to tell you I don't care
for latent semantic implementation details of Python? Anybody who does
what you just did should be laughed at derisively and ignored.  But I
don't have time to deal with fantasy and unreleastic theories.

> As I told you, there's no cure for idiocy.
>
> > Whee! And if one sober morning I want to
> > change the name __is_active to __buffer_is_active, I won't have to hunt
> > down 27000 lines of code to do it.
>
> And what if you want to change 'buffer_is_active' to 'is_active' ?
>

But I don't want to. I wanna change implementation not interface.

> > Also a naive third party won't crash
> > my system by changing Robust's state arbitrarily.
>
> Lol. cf above. And, may I repeat : you're getting the "my/3rd part"
> stuff the wrong way. If someone uses your code in it's app, then it's
> *her* system, and *your* code is the '3rd part'. Whether someone wants
> to do idiotic things with your code that will result in a crash is none
> of *your* concern. Just like if someone buy a hammer and bangs his head
> with, it's not the concern of the guy who made the hammer.
>

That's just silly. If a third party plugin is crashing your app, guess
who's gonna get the emails and bug reports? That's right you! And that
is after hours of trying to reproduce the bug on your system
unsuccessfully because you don't have the bloody plug-in installed and
they user doesn't know a random plug-in he downloaded is the root of
the problem. Welcome to reality.

> > Because in the real
> > world when your program is buggy, you get bug reports, nasty emails
> > among other forms of ridicule.
>
> So you see receiving a bug report as a form of ridicule ?
>

Yes, it can be.

> Now FWIW, I have lot of python apps in production, very few bug reports
> [1], and none of them being the result of the problem you seems to fear
> that much.

Good for you! I'm sure you are brilliant programmer.

>
> [1] The very first release of one of them is in production for more than
> 6 monthes now, is daily used by a dozen non-computer-savy users, and not
> a *single* bug report - actually, the only return we had is "it's
> perfect, it works like a charm, and we have some other stuff for you guys"
>

My users are not just end users they are also developers. Again, I'm
glad you are seeing success in __your__ projects.

>
> > And your supposed solution to my problem
> > is me saying, "but...but...I told you not change is_active."
>
> In my example (which was not intended as a "solution to a problem"),
> is_active is clearly part of the API. So your argument is moot.
>
> OTOH, if I need to control access to is_active, I can easily change it's
> implementation - ie by using a property (or any custom descriptor). So
> my "solution to the problem" is functionally equivalent to yours, and
> requires much less code - which contributes to making it more robust.
>

Your example actually requires more code, is looks complex and it's
ugly (no offense, my opinion).

> > Ha! And if
> > you can't figure out why anyone would do this,
>
> Oh yes, I can :
> - too much exposure to B&D languages
> - lack of ability to criticize "what's in the Book"
> - confusion between state/behaviour concepts and the (mostly inexisting
> in most hi-level languages) data/function dichotomy
> - control-freak mindset
>

Lets stick to the arguments please. No need to attack me.

> > then I'm not wasting my
> > time here anymore.
>
> You're wasting your time because you refuse to escape from your "what's
> in the book" mindest and insist on writing Java in Python. I had the
> same problem when I came from Java to Python, then I had the "aha"
> moment where I realized I was overdoing it, writing uselessly
> complicated code to do simple things that would just have worked without
> all this mumbo/jumbo control freak stuff. But it seems you prefer to
> stick to your masochistic approach for no other reason than
> misunderstood concepts, so we can't help you here.
>

Fantastically, I have never used Java for any public project. I don't
understand how you reach your faulty assumptions. You don't know my
background with any language so quit this "Java is the reason you think
like this" banter.

> > Someday you'll learn the hard way.
>
> Lol. I actually did *un*learn the hard way.
>
> Mystilleef, I've started programing 17 years ago, and have done it
> professionnaly for almost 10 years now. I do not pretend to be a good
> programmer, but please believe that I do know my job. I've read the Book
> too, I've tried applying it blindly, then I used my brain. Once you
> understand the real reasons behind a "rule", you also understand when
> and how to apply or not apply it.
>

What book are we talking about again? I made these rules from my
experience writing programs in Python, not from any book. There's only
so much books can do when it comes to designing robust software in
practice. But for a lot of people over here who claim they've been
programming for X number of years, some of them certainly do need to
hit the books again. I don't believe I spent an inordinate amount of
time explaining state and behavior or the benefits or techniques for
reducing coupling or why anyone would need accessors, among other
things.

> > Thanks to the people who exposed me to Python's properties.
>
> The problem is that you definitively *failed* to understand how to use
> them (or actually how to *not* use them when not needed).
> 

Sure, if it makes you feel better.