Accessors in Python (getters and setters)

[Bruno Desthuilliers]

mystilleef wrote:
> Bruno Desthuilliers wrote:
> 
>>mystilleef wrote:
>>
>>>Lousy Attribute Name:
>>>	self.tmp
>>>
>>>Accessors:
>>>	set_temporary_buffer
>>>	get_temporary_buffer
>>>
>>>The attribute name I chose, "tmp" sucks.
>>
>>Well, it's surely not as descriptive as 'temporary_buffer'
>>
>>
>>>I have used that name in
>>>dozens of places spanning over 27000 LOC.
>>
>>Too bad for you.
> 
> 
> Thank you, that was helpful.

What am I supposed to say ? You choose a bad name for a public symbol,
used it in 27000 lines of Python code (which certainly took some time to
write), and all of a sudden you realize the name is bad and proceed to
fix the problem. If you know of any other way than a massive
find/replace, please share. But blaming the language for your error
won't help.

> 
>>>There's a chance that other
>>>develops might misinterpret exactly what "tmp" does. Plus I don't want
>>>emails from other developers querying me about what "tmp" is/does.
>>>"tmp" is obvious to me, but not necessarily to others.
>>
>>So why did you name it that way at first ?
>>
> What does it matter? There are 10 million and one reasons from given
> identifiers bad names.

And how many reasons to use a bad name in 27000 LOCs before deciding to
fix the problem ?

> 
>>>Now compare that
>>>to the accessors.
>>
>>But 'tmp' actually *is* an accessor.
> 
> 
> I didn't say it wasn't.

Yes you did. May I quote ?
"""
"tmp" is obvious to me, but not necessarily to others. Now compare that
to the accessors. Not only do they improve readability at the expense
of more code, they actually allow me to change the lousily named
attribute "tmp" to "temporary_buffer" without grepping, seding,
searching, replacing and praying.
"""

This obviously implies that you don't understand 'tmp' as being an accessor.

>>>Not only do they improve readability
>>
>>Err... do you find:
>>
>>obj.set_temporary_buffer(val)
>>val = obj.get_temporary_buffer()
>>
>>really more readable than:
>>
>>obj.temporary_buffer = val
>>val = obj.temporary_buffer
> 
> 
> I didn't name the attribute temporary_buffer, I named it tmp.

You didn't name the *accessor* 'temporary_buffer', you named it 'tmp'.
You are *exactly* in the same situation as if you had used getter/setter
named "get_tmp" and 'set_tmp". And your point about getters/setters
"improving readability" is moot.

> 
>>>at the expense
>>>of more code,
>>
>>Indeed. In both the class and client code.
>>
>>
>>>they actually allow me to change the lousily named
>>>attribute "tmp" to "temporary_buffer" without grepping, seding,
>>>searching, replacing and praying.
>>
>>You still fail to get the point. You actually choose a crappy name for a
>>*public* property. It's *exactly* as if, in Java, you had named your
>>getter/setter 'get_tmp' and 'set_tmp'.
>> 
> 
> No, it isn't. 

May I quote what wou wrote a few lines above in this very same post ?
"""
>>But 'tmp' actually *is* an accessor.
>
>
> I didn't say it wasn't.
"""

Don't you see any contradiction here ?

> In Java there's a clear distinction between attributes
> and methods.

Yes, and that's a big weakness of Java. But that's another point, and
absolutely irrelevant here. Failing to understand a language semantics
gives no right to complain about the language.


>>>Sure, if you are dealing with less
>>>than a 1000LOC you can get away with using "tmp" or renaming it easily.
>>>But if you are dealing with a much larger code base and more
>>>developers, issues like this rapidly become a nuisance.
>>
>>Indeed. But it's *your* responsability to choose good names for the API.>
>  
> I choose good names for most of my APIs. But there cases when you never
> know an attribute will actually be an API before hand.

Then don't make it part of the API. And anyway, 27000 lines of Python
take some time to write, so you had the opportunity to address the
problem long ago - FWIW, you could have fixed it as soon as you noticed
you were accessing this attribute in client code.

> 
>>>Yes, it is possible to name crappy accessors too (e.g set_tmp/get_tmp).
>>
>>or 'tmp'.
>>
>>
>>>But developers tend to pay more attention to given methods/functions
>>>less crappy names, at least when compared to data attributes.
>>
>>s/developpers/you/> 
> 
> Ha, right! I bet you are perfect developer.

Certainly not, but I wouldn't confuse my own problems with a general
rule. Note FWIW that I wouldn't blame a language (or my lack of
understanding of that language) for my own errors.

>>>This
>>>stems from the fact that in many languages data attributes aren't
>>>usually part of the API,
>>
>>Once again, in Python, there is *no* such thing as 'data attributes'.
>>*All* attributes are *objects* - some of them callable.
>>
> I didn't say attributes weren't objects.

Nope, but you constantly bring that false "data/method" dichotomy in
your justifications for having badly named a public symbol.

> 
>>>as well as the whole OO(Encapsulation) blah
>>>blah.
>>
>>Don't confuse encapsulation with data-hiding. 
> 
> I don't see the confusion.

Was just an advice against a very common mistake.

>>>I know I would not name the accessors set_tmp/get_tmp, because my
>>>philosophy is that methods/functions need to have meaningful names and
>>>state their intended purpose.
>>
>>That's true for each and every name in a program.
>>
>>
>>>I don't hold data attributes to such
>>>standards
>>
>>Too bad for you.
>>
> Thank you.

For what ? You "don't hold data attributes to such standard". As a
consequence (and as a result of not having addressed the problem
sooner), you end up fixing 27000 lines of code. Too bad for you then.
Some would haved learned from the mistake, which then would have turned
into experience. Seems more and more obvious that you prefer to come
whining here instead and blaming the language for your own errors. Too
bad for you again.

> 
>>>and I imagine many developers don't either and least based on
>>>other people's code I've read. Plus there are many occassions when
>>>attributes are not intended to be APIs,
>>
>>Then mark them as being implementation (ie : prefix them with a single
>>underscore).
>  
> I thought that too was unpythonic.

It's a well-known convention, as you would have noticed if you had read
some existing python code, read PEP8, or just looked/asked for Python
naming conventions. FWIW, that's one of the first thing I learned with
Python.

>>>but eventually become one.
>>>After all most data attributes are created with the purpose of serving
>>>methods.
>>
>>Nope. You have the class API, and the class implementation. Both made of
>>both callable and non-callable attributes.
>>
> 
> Or objects have state and behavior. Data attributes represent state and
> methods represent behavior.

Is a getter "behaviour" ? If yes, how does this differ from public
"data" attributes from a semantic POV ?


>>Mystilleef, I do share your pain (really - been here, done that,
>>etc...), and I understand that grasping Python requires some mental
>>adjustments when coming from Java and friends (been here, done that,
>>etc...). But you seriously can't blame the language for your own mistakes.
> 
> You don't share my pain.

Are you me to know what I feel ?

> You seem to mock it.

Compassion doesn't imply agreeing on wrong arguments.

> I'm not new to Python
> either.

New enough to not understand how Python's object model, semantic and
overall philosophy strongly differs from Java/C++.

> I've been using it for over 2 years in several capacities. I
> only recently decided to use it for a large project.
> 
>>If you intented 'tmp' to be part of the API, then you're responsible for
>>the bad naming.
> 
> 
> I never intended it to be part of the API. 

So you should not have used it outside the class.

> It evolved to be an
> important part of the system.

Then you had plenty of occasions to address the problem.

> 
>>If you didn't, then you're responsible for breaking the
>>encapsulation - FWIW, following the convention (single leading
>>underscore) could have make it clearer to you.
>>In both cases, you
>>happily used a bad name in 27 KLOC - so you really had a lot of time and
>>occasions to notice something wrong with this.
>>
> 
> That's nonsense.

Your opinion. Facts tell otherwise.

> I only just noticed because I was trying to implement
> a plug-in system and I needed to expose an important class. I would not
> have considered the issue a problem without this requirement. Except
> you are a prophet, you sometimes can't know before hand how certain
> classes will end up being used especially if requirements suddenly
> change.

Yes, that's something I'm well aware of. And that's why I pay attention
to naming and to interface/implementation separation.

> Saying it's my fault to make yourself feel better about your
> favorite language doesn't help solve my problem.

I don't say it's your fault to "make (myself) feel better about (my)
favorite language, but because the problem is entirely and only yours.
Python has it's share of warts, and I'm not denying it.

> I didn't come here to
> be berated. 

Nope, but you came here blaming the language for your own errors, and
constantly refuse to aknowledge that *you* got it wrong.

> I came here to learn the Pythonic way to implementing
> accessors. 

With public attributes when there's no processing to do, with computed
attributes (based on descriptors, property being the most commonly used)
else. But this is totally unrelated to the issue with badly chosen
public names.

> And of course how to deal with issues like the one I have in
> medium size to large scale projects. People make mistakes, we deal with
> an move on. 

When one makes mistake, one can either choose to aknowledge the fact and
learn from it, or to find something/someone else to blame and not learn
anything.


-- 
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb at xiludom.gro'.split('@')])"