Re: Basic inheritance question

Please stop taking my words to its letters.

So we're supposed to actually guess what you really mean ???

That's what human does, otherwise you'll "Fail the Turing Test".

Personally, I've seen many C++ programs with complex class designs
where it definitely helps to consistently use "this->". I cannot
remember all local (and global) variables in bigger methods.

In that case, you have the _option_ to do it.

Make no sens when maintaining code wrote by someone that didn't use this
'option'.

(snip)



it's the first argument of the function - which usually happens to be
the current instance when the function is used as a method.
And that's the point, self (or anything you name it) is almost always
the current instance
# this is a plain function. In this function,
# 'obj' can be whatever that happens to have a (numeric)
# 'stuff' attribute
def func(obj, arg):
   return (obj.stuff + arg) / 2.0

# this is a class with an instance attribute 'stuff'
class Foo(object):
    def __init__(self, bar):
      self.stuff = bar + 42

# this is another (mostly unrelated) class
# with a class attribute 'stuff'
class Bar(object):
   stuff = 42

# this is a dummy container class:
class Dummy(object): pass

# now let's play:
import new

d = Dummy()
d.stuff = 84
print func(d, 1)

d.baaz = new.instancemethod(func, d, type(d))
print d.baaz(2)

f = Foo(33)
print func(f, 3)
Foo.baaz = func
f.baaz(4)

print func(Bar, 5)
Bar.baaz = classmethod(func)
Bar.baaz(6)

 and that makes it functionally the same as Me and
this in VB and Java.
Depends on the context, cf above !-)

Please again, stop taking letters to the words, I don't meant them to
be exactly the same, rather the same would meant that they generally
can be considered equal,

If you still think that way after having read the above code, then I
can't help. We obviously don't share the same mental model here.

I don't get what you're trying to meant, in that piece of code self is
used in the regular way, in a regular context.

exceptions exists of course. And btw, I don't
understand what you meant by your example, they seemed to be a
completely OK program for me,

Indeed it's ok (even if totally useless by itself). The point is that
'self' (or whatever you name it) is just and only the first argument of
a function, period.

And it is... but I still don't get what you meant

even though it's a bit confusing to
follow[2].

Nothing in it should be confusing to anyone having a decent knowledge of
Python's object model IMHO.

[2] btw, the reason it's a bit confusing to follow is one of my
points: It is a Bad Thing(tm) to use the same name for different
variables

Where do I "use the same name for different variables" here ?

It's not confusing in the way of object model, but in the way that you
used meaningless names in overloaded manner.

even in a language like Python that enforce explicit naming
of classes

Python doesn't "enforce" explicit name of classes - IIRC, there are ways
to instanciate anonymous class objects. But I definitively don't see how
this relate to this discussion.

We're not talking about anonymous class objects here, and I'm sure you
actually understand what I meant by "naming the class" from previous
discussions.

Yes, I know, "please guess what I mean" !-) but sorry, there's no sens
discussing a technical point without using accurate and appropriate
technical naming of technical concepts invlved.

Well, it's not my fault for being born as a non-native speaker of
English, sometimes what I meant might goes a bit off from what I
write. Anyway, human languages aren't designed to be fully
unambiguous, so it is natural for human to provide a margin of errors
when speaking to each other, well unless you're not a human...

Most other languages
1) automatically assign the containing class' object
s/containing class' object/current instance/
in a keyword
(Java: this, VB: Me) behind the screen,
That's not very far from what a Python method object does -
automatically assign the current instance to something. The difference
is that Python uses functions to implement methods (instead of having
two distinct contructs), so the only reliable way to "inject" the
reference to the current instance is to pass it as an argument to the
function (instead of making it pop from pure air).
It isn't very far, but Python makes it obvious about the assignment
(not behind the screen).
Exactly. And given both the simplicity of the solution and what it let
you do, that's a *very* GoodThing(tm) IMHO.

I agree, it's a Good Thing but it doesn't make the point less pointy,
the difference between Me/this and self is just the explicit
assignment. Other things that is possible because of the explicit
assignment is just a "coincidence" of design choice.

Are you sure ? As far as I'm concerned, I think that the design choice
somehow results from what it makes possible.

It's correct, IF you see it traversing from the past, when many design
choice is being made for any possible features that is required. If
you dumped the past for a while, it is just a "coincidence" of design
choice.

And it is always a Bad Thing(tm) to use the same name for two
variable in the class and in function (which is the main and only
source of possible ambiguity) in ANY language, even in Python.
Ho, yes.... Like, this would be bad ?

class Person(object):
   def __init__(self, firstname, lastname, birthdate, gender):
     self.firstname = firstname
     self.lastname = lastname
     self.birthdate = birthdate
     self.gender = gender

C'mon, be serious. It's often hard enough to come with sensible names,
why would one have to find synonyms too ? Try to come with something
more readable than the above, and let us know. Seriously, this braindead
rule about  "not using the same name for an attribute and a local var"
obviously comes from languages where the "this" ref is optional, and
FWIW it's obviously the wrong solution to a real problem (the good
solution being, of course, to use the fully qualified name for
attributes so there's no possible ambiguity).

The code fragment you've given way above (about the Foo, Bar, bazz,
and func) also suffers from the bad habits of using the same name for
different variables.

Where ? And how does this answer the question above ?



And it's not a "braindead" rule

The way you express it, and as far as i'm concerned, it is, definitively.

Perhaps I forgot to say that always might still have exceptions.

The example you've given IS the most readable form since the function
is _simple_, consider a function that have complex codes, possibly
calculations instead of simply assigning initial values I'm sure you'd
slip up between the self.* variables and the * variables once or
twice,

*you* would perhaps have this problem. And you would indeed have this
problem in Java or C++. In Python, this problem just don't exist.

No it exists in any language, the way to avoid it is by good class
design.

possibly becoming the source of hard-to-find bugs.

Consistant and intelligible naming is quite another problem. And it's
too much dependant on the context, language, domain and whatnot for any
rule like your one above to be universally applyable.

It is universally applicable, with some exceptions of course, such as
in a field where there is no agreed naming convention yet.


And in languages that doesn't enforce explicit naming of classes,

I still don't understand how all this relates to the naming of class
objects ?

Oops, sorry: you meant "in languages that has implicit instance
reference available in methods" ? Python doesn't have it, so any rule
deriving from this "feature" is out of scope here.

 when
there is the two or more same names, the one with the smallest scope
is picked, so in _simple_ functions, the trick of using full qualified
names and overloaded local names is still possible and feasible. In
complex functions, the trick fails even in Python, because even if
Python and our full-concentration-brain is aware of the difference
between self.* and *, our spreaded-concentration-brain that is
scanning the code for the source of bugs might get stumbled on the
confusing use of self.* and *.

Here again, *you* may have this problem. I don't, since I always used
explicit instance reference.

I don't have that much of a problem, I only pointed out that it is
possible to miss the names overloading in quick scanning. The reason
why you never get stumbled is possibly because your brain memorizes
the names and doesn't even understand what a name actually meant. This
halved the reason of spending some time to find a meaningful name.
With your brainset, it is just possible to create a program fully with
names like foo and bar and never get stumbled. In this case, it
excels, but it's a poor man's way of trying to be smart.

Anyway, I actually know 3 languages (4 if C# works the same) that has
this implicit 'this' (or whatever the name) 'feature', and at least 5
that don't. So I'm not sure that the "most other languages" qualifier
really applies to point 2 !-)
What's this 5 languages?
Smalltalk, Python, PHP, javascript, Ruby. I don't remember how Scheme,
CLOS and OCaml handle the case.

Among all them, only Javascript is considerably mainstream.

Is that a joke ? PHP is probably the most used language for web apps
(server side of course). And Python is certainly not an obscure unknown
geek-only language no more. But anyway: you were talking about "most
other languages" - not "most mainstream languages".

Yes, I'm aware that Python and PHP indeed have larger user base than
perhaps smalltalk and Ruby, but nevertheless they're middle sized.
What's I'm talking about mainstream is large as in large, not medium.
PHP's domain has lots of competition, ASP, JSP, CGI, etc and this
market is very fragmented, even though server-side scripting plays
important role in the Internet, the role of each language is lessened
because of the fragmentation making none of them mainstream enough.
Python is shaded by Java in the market for ultra portable (VM)
language. And I'm not talking about Smalltalk and Ruby here.

Are they a mainstream, high-level languages
or lesser known, low-level languages? C-family, Java, and Basic are
the Big Three of high-level programming language.
None of C, C++, Java nor Basic qualify as "hi-level". C is the lowest
possible level above assembly, C++ is often refered to as an "object
oriented assembler", Java is way too static, crippled, verbose an
unexpressive to qualify as "hi-level" (even if it suffers from some
problems usually associated with higher level languages). I won't even
comment on basic (is that really a language at all ?).

Your criteria on being high-level is simply just odd.


My criteria on being hi-level seems quite common: automatic memory
management, portability, "rich" builtin data types, functions as first
class citizens, lexical closures, strong introspection features, strong
metaprogramming support, etc...

We're talking language-wise here, not the implementation, and those
criteria are for implementations. It is the case where we blindfold
our eyes against "the things behind" and see only the language from
the front. Yeah, perhaps "the things behind" would have some effect to
the front side, like it is possible to create C with automatic memory
management with little change in the language itself, it's possible to
have more built-in datatypes than the standard set without major
change in language itself. These are the criteria for language-wise
comparison.

The rest of the
world recognizes C-family, Java, and Basic as high-level languages.

C was "hi-level" wrt/ assembler, indeed. And Java is "hi-level" wrt/
C++. Ho, and _please_ don't get me started on basic !-)

And the world is content with that. C is probably the lowest shade a
high level language could be, but it is still a high-level.

If I have to say it, Python is actually lower level than Basic.

Language-wise, indeed it is. Implementation-wise, Python might be
higher than Basic.

While
Java is just below Python and C and C++ is just below Java. Why do I
consider Basic the highest-level? Because it is the cleanest to scan
(no confusing symbols, i.e. no curly braces, no confusing use of
parens (Python uses (), [], and {}, VB only use ()[3]),

Basic != VB. There are quite a few other basics here.

I'm aware of that, but VB is the one with the largest user base, and I
think it could be used to represent the language as a whole. And
VB.NET is one with possibly the highest shade of level among other
Basics.

Now if you choose this criteria, you may want to learn some Lisp dialect.

In what way C++ resembles an assembler?

C++ is some OO stuff bolted on a very close-to-the-metal language itself
designed to write operating systems, drivers and other low-level stuff.

In what way is C++ close to the metal? It's very far actually, C-
family don't have a one-to-one relationship with assembly or plain
executable binary.

Have you ever programmed in
assembly?

I did.

And surely you'd realize that the level of C and assembly is very far,
perhaps the furthest leap in programming language level.

How hard is it to create a simple program in assembly? And
how hard is it to create a complex program in C++

Roughly the same, thanks to scoping rules, dependencies hell, lack of
automatic memory management and overcomplex features.

By saying that you've revealed that you missed my point too far. There
is no point to continue talking about A when you're talking about B.

(which AFAIK is used
by hundreds of mega projects including CPython)?

CPython - as the name implies - is written in C.

And by saying that I'm sure you agree that even C, which is lower
level than C++ is high-level enough to be used in large projects like
CPython. I'm interested in seeing Python implemented in pure assembly,
perhaps asmPython?

And have you ever used Basic at all?

I did. And not only VB.

Some programmers would instantly frown upon Basic, simply because they
don't know that Basic is "just another language".

I've used at least four different variants of Basic.

Then with such experience in Basic you should realize that Basic isn't
much off from other languages.

In VB, Me is extremely rarely used,
I used to systematically use it - like I've always systematically used
'this' in C++ and Java.
And that is what reduces readability. A proficient VB/C/Java
programmer
There are quite a few proficient C/C++/Java programmers here. As far as
I'm concerned, I would not pretend being one - I just have a good enough
knowledge of C, Java and (alas) VB to be able to get up to speed in a
reasonnable time frame.
As a side note, the problem just doesn't exists in C, which has
absolutely no support for OO.
When I said C, it might mean C and C-family,
When you say "C", it means "C" to everyone reading you.

Depending on the context, it's easy to rule out which means what.

so please stop
misunderstanding me.

Please learn to express yourself clearly. If you say "X" when you mean
"Y", *you* are the one responsible for misunderstandings. This is human
communication 101 skill.

Even computers are designed to tolerate errors in data transfer, then
human is less intelligent than computers you say?

would frown upon the extra, unneeded garbage as they
thought it was clear already that the variable refers to a class-level
variable.
In C++, the canonical way to make this "clear" is to use the m_name
convention. There must be some reason C++ programmers feel a need for
this "extra, unneeded garbage" ?-)

In some cases, an extremely complex class that can't be fragmented any
further, the m_ convention is surely useful, but in most cases you
could skip them out.

You "could" skip this convention, but it's really considered bad
practice by quite a lot of C++ programmers.

Bad, because a lot of them are already accustomed to it and it have
become a de facto "rules".

And the canonical way to make this "clear" is not
the m_ convention, it's the name itself. A well-designed class would
choose names that is recognizable instantly from the name itself, even
without the pseudo-name appended to it (or prepended).

I await for your exemples.

btw you must have been memorizing names braindeadly, because the only
way you could stumble on that is by memorizing names braindeadly.
Names shouldn't be memorized, it should be inferred and memorized. For
example, when you met a variable name firstname and lastname inside a
class called Person, you'd immediately realize that it is Class Level
variable because you know that the function you're currently working
on use the name initialfirstname and initiallastname.

Fine, I now have four names to handle, each of them being possibly an
argument, a local variable, a member variable or a global variable. Great.

Sorry but I won't buy this.

THAT'S the point. You are unable to infer that the name
initialfirstname and initiallastname is a local variable, since it is
quite impossible for something initial to be a member variable or
global. If it is a global, it shouldn't be named initial, perhaps
default, if it is member variable, it should be plain vanilla
firstname and lastname. This is called inferring scope from name.

As I've pointed out, there is little harm in class-level variable's
implicit reference.
Have some working experience on any non-trivial C++ project ?

No

I would have been surprised if you had answer otherwise.

(you could say I'm a student so I've never "worked"[1]). But I've
done some medium-sized projects in other languages.

[1] If you understand the irony, you'd realized I was deliberately
misunderstanding you

Not sure.

Don't cut my words apart, it's meant to be together or it lose its
sense of humor.


Compare the following codes:
VB.NET:
Public Class A
Dim var
Public Function aFunction()
return var
Add three levels of inheritence and a couple globals and you'll find out
that readability count !-)
It's the mental model that have to be adapted here, if the current
class is inheriting from another class, you've got to think it as
names from parent class as it is a native names, so you don't actually
need to know where the variable comes from
In C++ (and VB IIRC), it might as well be a global So sorry but yes, I
have to know where it comes from.

How many times would you use globals, it is a Bad Thing(tm) to use
globals in the first case.

It is, most of the time, indeed.

The problem is that you rarely start a project from scratch - most of
the time, you have to work on legacy code. And you really seldom have
the possibility to do a major rewrite to fix all warts.

But it is always possible to reduce the most critical of all of them.

In some exceptional cases globals might be
unavoidable, but it is trivial to work out that you have to reduce the
amount of globals to a minimum, in almost any cases to a number you
can use a hand to count with.

That very nice, from a theoretical POV. That's alas just not how it
works in real life.

A bit utopic, I agree, but it's always possible.

And applying the hacks mentioned, why
don't you use the m_ convention for globals, and retains the
convenience of m_-free variables in your class variable. You use class
variable much more often than globals, and in most projects class-
level variable is used just as often as local-variable.

The problem is not what *I* (would) do, but how is the existing code.

since knowing where it
comes from is breaking the encapsulation
Nope, it's knowing what you're doing and how the piece of software at
hand is working. And FWIW, while data hiding is one possible mean of
encapsulation, it's by no way a synonym for encapsulation.

I agree that knowing an underlying class's implementation is useful
(in fact, very useful) but what I'm talking is about should-ness,
we
shouldn't _need_ to know the underlying implementation,

How can you hope to extend a class without _any_ knowledge of it's
implementation ?

By knowing its interface is usually enough to extend a class.
(USUALLY!)

(which, in Python is very
weakly implemented, which favors flexibility in many cases[1]).
[1] In Python, it is impossible to create a completely private
variable, which is the reason why the mental model of these other
languages doesn't fit Python.
Never heard about the infamous '#define private public' hack in C++ ?
And don't worry, there are also ways to get at so called 'private' vars
in Java.

No, but it's violating the language's rule.

Nope. It's just making use of some part of the language's rules.

No, its a hack that should be illegal, a kind of abuse of rules.

Python OTOH, provides
formal ways to got to private vars.

Python doesn't have "private vars" at all.

THAT'S the point. Even __vars and _vars that are supposed to be
(semantic-wise) the private variable of Python is accessible from
outside while still using a formal ways of accessing it (instead of a
hack)

It's easy to keep track of globals, as you shouldn't have a
lot of them even in a huge project.

Can't you understand that starting a new project afresh is *not* the
common case ?

But I'm sure even an old, dirty codes wouldn't usually have as much
global as a twenty pages listing of globals. If they do, then just
quit that job.

As a final note:
I don't think implicit class reference is superior to explicit class
reference, neither
...

I'm sure you don't believe it since I'm talking on implicit's side,
but that's the fact, I just pointed you out that implicits do have its
positive side (even if you don't consider them positive in _your_
book) but that doesn't meant I believe it is better than the other.

To clear things up:
As a final note:
I don't think implicit class reference is superior to explicit class
reference, but I don't think the vice versa is true either.

Once again : what classes have to do with this ?

Seriously, how can you hope to be taken seriously when you're obviously
confusing such important concepts as instance and class ?

I'm struggling with English as of now, so please make me more confused
by having to choose the most proper terms, when it is easy to rule out
what I meant.

This is going to be my last two cents on this topic. I'm tired of this
pointless discussion. We could like a language even though we have
principal differences on how to see the language and how to think
about it.
.

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