"Michael Geary" <Mi**@Geary.com > wrote ... Does anyone have some sample code where obj$func() would be used?
(Apologies if I missed it.)
There have been so many messages about delegation and binding since Greg
originally posted his meowing cat message that it's hard to remember what
the original problem was that Greg pointed out. At that time Prothon had no
solution for the problem. Now there is a released solution but it is
incomplete and has broken the xor operator ( ^ ) (don't tell anyone <grin>).
I'll restate it here in my own way (this is copied from something I posted
on comp.lang.py).
Statement of problem (These are tested programs from released Python and
Prothon:):
# Python
class klass:
def __init__(self):
self.me = 1
def func(self):
print "func1,self"+st r(self.me),
class klass2(klass):
def __init__(self):
self.me = 2
def func(self):
klass.func(self ) # delegation
print "func2,self"+st r(self.me),
inst = klass2()
inst.func() # prints func1,self2 func2,self2
# Directly translated to Prothon
Klass = Object()
with Klass:
.me = 0 # extra line
def .__init__():
.me = 1
def .func():
print "func1,self"+.m e,
Klass2 = Klass()
with Klass2:
def .__init__():
.me = 2
def .func():
Klass.func() # does not do what python does
print "func2,self"+.m e,
inst = Klass2()
inst.func() # prints func1,self0 func2,self2
As you can see, the call Klass.func() got the function func from the object
Klass and then called it on Klass using Klass as the target "self" instead
of the instance "inst". This is not what Python did and this is the
problem.
In Python the call klass.func() was different because Python knows that
klass is a class and therefore obviously cannot be the target of call (an
instance), so it made the programmer pass the instance self to use as a
parameter.
To fix this, we need to be able to specify in general, what the self object
is going to be during the execution of a function in Prothon (I call this
choice of self "binding self to function" even though it's temporary during
execution).
Greg's solution was to replace the period before the function name in
klass.func() with a different symbol to indicate that the func is not
supposed to be bound to klass as the syntax normally suggests (as in
list.sort!()), but instead defaults to the current self. My final scheme is
almost the same but instead of just defaulting to self, it specifically
forces it to self (this may seem like a semantic difference, but don't say
that to Greg <grin>).
So now we have this solution. Note that delegation to an ancestor prototype
(class in Python), is a common operation, especially in the __init__
function:
Klass = Object()
with Klass:
def $__init__():
$me = 1
def $func():
print "func1,self"+$m e,
Klass2 = Klass()
with Klass2:
def $__init__():
$me = 2
def $func():
Klass$func() # voila! problem fixed
print "func2,self"+$m e,
inst = Klass2()
inst.func() # prints func1,self2 func2,self2 90  3957 
My apologies. I posted this to c.l.p. by accident. I meant to post this
to Prothon-users.
"Mark Hahn" <ma**@prothon.o rg> wrote in message
news:d2Uhc.2227 2$dZ1.1600@fed1 read04... "Michael Geary" <Mi**@Geary.com > wrote ...
Does anyone have some sample code where obj$func() would be used?
(Apologies if I missed it.)
There have been so many messages about delegation and binding since Greg
originally posted his meowing cat message that it's hard to remember what
the original problem was that Greg pointed out. At that time Prothon had
no solution for the problem. Now there is a released solution but it is
incomplete and has broken the xor operator ( ^ ) (don't tell anyone
<grin>). I'll restate it here in my own way (this is copied from something I posted
on comp.lang.py).
Statement of problem (These are tested programs from released Python and
Prothon:):
# Python
class klass:
def __init__(self):
self.me = 1
def func(self):
print "func1,self"+st r(self.me),
class klass2(klass):
def __init__(self):
self.me = 2
def func(self):
klass.func(self ) # delegation
print "func2,self"+st r(self.me),
inst = klass2()
inst.func() # prints func1,self2 func2,self2
# Directly translated to Prothon
Klass = Object()
with Klass:
.me = 0 # extra line
def .__init__():
.me = 1
def .func():
print "func1,self"+.m e,
Klass2 = Klass()
with Klass2:
def .__init__():
.me = 2
def .func():
Klass.func() # does not do what python does
print "func2,self"+.m e,
inst = Klass2()
inst.func() # prints func1,self0 func2,self2
As you can see, the call Klass.func() got the function func from the
object Klass and then called it on Klass using Klass as the target "self" instead
of the instance "inst". This is not what Python did and this is the
problem.
In Python the call klass.func() was different because Python knows that
klass is a class and therefore obviously cannot be the target of call (an
instance), so it made the programmer pass the instance self to use as a
parameter.
To fix this, we need to be able to specify in general, what the self
object is going to be during the execution of a function in Prothon (I call this
choice of self "binding self to function" even though it's temporary
during execution).
Greg's solution was to replace the period before the function name in
klass.func() with a different symbol to indicate that the func is not
supposed to be bound to klass as the syntax normally suggests (as in
list.sort!()), but instead defaults to the current self. My final scheme
is almost the same but instead of just defaulting to self, it specifically
forces it to self (this may seem like a semantic difference, but don't say
that to Greg <grin>).
So now we have this solution. Note that delegation to an ancestor
prototype (class in Python), is a common operation, especially in the __init__
function:
Klass = Object()
with Klass:
def $__init__():
$me = 1
def $func():
print "func1,self"+$m e,
Klass2 = Klass()
with Klass2:
def $__init__():
$me = 2
def $func():
Klass$func() # voila! problem fixed
print "func2,self"+$m e,
inst = Klass2()
inst.func() # prints func1,self2 func2,self2
Mark Hahn wrote: My apologies. I posted this to c.l.p. by accident. I meant to post this
to Prothon-users.
Oh, no problem, there's some Python content (see below for some comments
on it)...
.... # Python
class klass:
def __init__(self):
self.me = 1
def func(self):
print "func1,self"+st r(self.me),
class klass2(klass):
def __init__(self):
self.me = 2
def func(self):
klass.func(self ) # delegation
print "func2,self"+st r(self.me),
inst = klass2()
inst.func() # prints func1,self2 func2,self2
....
In Python the call klass.func() was different because Python knows that
klass is a class and therefore obviously cannot be the target of call (an
instance), so it made the programmer pass the instance self to use as a
parameter.
This isn't really a very clear description of what's going on in
Python. It won't matter to the Prothon users, but don't want any Python
users to get confused...
Looking up klass.func returns an unbound instance method, this is a
function wrapper which basically just says "hey, you're a member
function of a class, check to be sure that your first argument is a
member of that class". This is done by the function's descriptor
hooks which allow it to return a wrapped object when the user
attempts to retrieve the value from another object (such as a class
or an instance). So, in a sense, yes, the class cannot be the
target of that *particular* call, as the unbound method object you
retrieved will reject anything other than an instance of the class.
Bound instance methods are a similar wrapper, but they say
"curry/bind your first argument (normally self) to this value then
call the underlying function". They are created on object.method
access by the same function descriptor hooks.
The point of all that being that classes most definitely *can* be the
target of a call. Python's classes are first-class objects. In
particular, they are instances of metaclasses, and can have meta-methods
defined which take the class as their first parameter just like a normal
method-call.
class k(type):
.... def r( cls ):
.... return 42
.... class x:
.... __metaclass__ = k
.... x.r()
42
There's very little "special" about classes other than that they have
some syntactic shortcuts for creating them and for looking up attributes
of their instances within them. Python isn't looking at every method
call and saying "hey, that's a class, that can't be the first parameter
to a function/method!", it (particularly the unbound instance object) is
saying "hey, you're not an instance of my class, go to heck" and never
thinks about whether the object is *particularly* a class or not.
Classes are special in Python, but not nearly as special as you might
think from a class-less perspective :) ,
Mike
By the way, the modern Python idiom is:
super( klass2, self ).func( )
but that wouldn't help in explaining the logic for the Prothon
choice, so no biggie :) .
_______________ _______________ _________
Mike C. Fletcher
Designer, VR Plumber, Coder http://members.rogers.com/mcfletch/
Mike C. Fletcher wrote: This isn't really a very clear description of what's going on in
Python. It won't matter to the Prothon users, but don't want any
Python users to get confused...
My inability to understand this stuff is what drove me to do Prothon <grin>.
All the hidden wrapped this and wrapped that confused me to no end.
By the way, the modern Python idiom is:
super( klass2, self ).func( )
You're kidding. That seems like a big leap backwards in friendliness. Kind
of a syntax castor oil.
That's explains why Joe Mason did his proposal for Prothon delegation using
that same idiom for Prothon. I thought he was somewhat crazy wanting us to
type all that each time.
What problem caused Python to want to switch to such a general operation?
What is the usage case that is so important that it is making eveyone wear
out their keyboards typing that monstrosity?
Oh well, I guess it gives me one more argument to pitch for Prothon...
Mark Hahn wrote: My inability to understand this stuff is what drove me to do Prothon
<grin>.
All the hidden wrapped this and wrapped that confused me to no end.
... You're kidding. That seems like a big leap backwards in friendliness.
Kind
of a syntax castor oil.
Says the guy who's introducing a new operator to his language before
even understanding the behavior of the original one, by his own
admission ...
--
__ Erik Max Francis && ma*@alcyone.com && http://www.alcyone.com/max/
/ \ San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
\__/ Human love is often but the encounter of two weaknesses.
-- Francois Mauriac
"Erik Max Francis" <ma*@alcyone.co m> wrote ... Says the guy who's introducing a new operator to his language before
even understanding the behavior of the original one, by his own
admission ...
Well, I do tend to exaggerate a bit. I can understand it when I study it,
but in everyday coding it does not roll off my fingers. Also, it is
possible to design something new without understanding the old. It might
even be an advantage in some circumstances to not be tainted by old
concepts.
I am serious when I say I think that Python has headed off into egghead land
a bit and I feel that keeps a lot of people from switching to it. I think
that this heady stuff scares them off. I really am trying to make things
simpler in Prothon. Now, whether I can succeed or not is another question.
Only time will tell.
Mark Hahn wrote: Well, I do tend to exaggerate a bit. I can understand it when I study
it,
but in everyday coding it does not roll off my fingers. Also, it is
possible to design something new without understanding the old.
It is _possible_. But it is not a very good idea.
I am serious when I say I think that Python has headed off into
egghead land
a bit and I feel that keeps a lot of people from switching to it. I
think
that this heady stuff scares them off. I really am trying to make
things
simpler in Prothon. Now, whether I can succeed or not is another
question.
Only time will tell.
Other than the basic premise of Prothon, every single decision I've seen
you make (or consider) looks wholly stylistic, awkward or even arcane,
and the opposite of the one I, or I think Guido, would have chosen.
Being a fan of Io, I think prototype-languages are interesting. Even so
far, I lost interest in looking at the actual main feature of Prothon,
after seeing all the extra baggage that was brought on in unecessary
stylistic changes.
Seriously considering every single possible proposal is not
constructive. Without a strong sense of what the language should look
like, Prothon is going to continue to look more and more like Perl.
It's already most of the way there.
--
__ Erik Max Francis && ma*@alcyone.com && http://www.alcyone.com/max/
/ \ San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
\__/ I love Mickey Mouse more than any woman I've ever known.
-- Walt Disney
Mark Hahn wrote: I am serious when I say I think that Python has headed off into egghead land
a bit and I feel that keeps a lot of people from switching to it. I think
that this heady stuff scares them off.
Not likely. Most people learning or using Python still have little
interest in or need for metaclass programming, and I *strongly*
doubt it has scared off more than a handful of people.
Likewise, the differences between prototype-based languages and
class-based languages do not appear significant enough to be
the sole reason to pick one over the other. The community,
on the other hand, and the libraries -- well, those are good
reasons for picking Python. It will be interesting to see whether
Prothon manages to achieve similar success in either area.
And if it does, well, see my first point in this sentence again...
-Peter
Mark Hahn wrote: Mike C. Fletcher wrote: By the way, the modern Python idiom is:
super( klass2, self ).func( )
You're kidding. That seems like a big leap backwards in friendliness.
Don't worry, the traditional form of super call in Python
isn't going away any time soon. It's not replaced by this;
they do different things.
The new form is occasionally needed, but not very often.
I haven't found a use for it myself yet. (I *thought* I
had found one the other day, but it turned out I hadn't.)
--
Greg Ewing, Computer Science Dept,
University of Canterbury,
Christchurch, New Zealand http://www.cosc.canterbury.ac.nz/~greg
"Peter Hansen" <pe***@engcorp. com> wrote ... It will be interesting to see whether
Prothon manages to achieve similar success in either area.
I apologize if I got competitive. As I have said many times, I don't
expect Prothon to compete with Python. It's hard to bust your butt on
something day in and out without getting carried away. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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