---------- Forwarded message ----------
From: doug shawhan <[EMAIL PROTECTED]>
Date: Oct 26, 2006 1:45 PM
Subject: Re: [Tutor] Self, Scopes and my unbelievable muddleheadedness.
To: Alan Gauld <[EMAIL PROTECTED]>
On 10/26/06, Alan Gauld <[EMAIL PROTECTED]> wrote:
I've always been confused by much of the OOP terminology. I'm about to go off on a tangent below regarding your explaination. I think it is helping me, but I want to be sure. Bear with me. :-)
My original question should have been:
"Why is this dictionary coming back weird?" The dictionary was just a placeholder for a future .ini file to be read with ConfigParser. In playing around with different ideas. I thought "I'd like to put each particular set of activities into modules anyway, so let's just figure out how that might work".
I ran onto the problem of the dictionary being changed globally, when I thought that use of "self" meant that any changes to that data were limited to the scope of the method in that particular class (and it's resultant object), thereby insulating it from other methods in the same class and other objects which inherit from the same class" (Don't reply to this yet! :-)
I'm sure that I have simply thought that my global declaration was not going to be changed in place by misunderstanding what "self" means. My confusion stemmed from just how weird the change appeard to be. I.e. "But I just looked at the dang thing and it was what I expected! Where dem extra parentheis come from? Huh?"
I apologize for my incoherence in asking the question. I was in the middle of trying out different ideas and ran onto this weirdness and could not let it go. I should taken the time to write a generic example, but frankly, I was frustrated and was not thinking about how best to frame the question. It was impolite of me to subject the list to my half-baked meanderings. Again, sorry. You guys have helped so much and you deserve a little more effort on my part.
So, fortified with 8 hours of sleep and 15mg of Adderall, here we go!
I felt like I was being told an integer is a "counting number" here. ;-)
I was even more confused. Were you objecting to my nomenclature?
So I thought, "If I named the class "Steve" and called the methods createFreshDB() and createComparisonTable() so it would read:
"Steve, create a fresh database which includes tables named for the keys and columns named for the values in this dictionary I'm handing you."
"Steve, create a comparison table just like above, but with a different key."
which would be followed (eventually, if I hadn't gotten bogged down) by
"Steve, tell gadfly to collate those two tables I just had you make and put them in another table so I can generate a report"
Would that make any difference?
No especially in how the code was written (it was still ugly and half-baked, and showing tons of bad habits), but I did suddenly realize what you meant by "noun".
I have been treating objects like a corporate sales droid treats nouns.
I've been "Gifting" and "Tableing" the objects "TheGift" and "TheTable" in my mind. (I fear I've also been "Impacting" the method "impact()" without asking Steve.Please() first, (I.E. not quite understanding why my classes within the modules were not showing up like I expected, but that's another story.)
I've not been thinking of an object as a verb, rather more like a gerund. Still wrong, but a different kind of wrong.
Which leads me back to the "why is it there?" question I saw on the list recently.
As I said, all that stuff was throwaway anyway and I should have made a more generic example.
Thanks!
"doug shawhan" <[EMAIL PROTECTED]> wrote
> I'm having a rather difficult time understanding the proper use of
> "self".
Doug, I think you may be having a more fundamental problem.
Looking at your code at the most superficial level it seems
you may not understand objects.
I've always been confused by much of the OOP terminology. I'm about to go off on a tangent below regarding your explaination. I think it is helping me, but I want to be sure. Bear with me. :-)
My original question should have been:
"Why is this dictionary coming back weird?" The dictionary was just a placeholder for a future .ini file to be read with ConfigParser. In playing around with different ideas. I thought "I'd like to put each particular set of activities into modules anyway, so let's just figure out how that might work".
I ran onto the problem of the dictionary being changed globally, when I thought that use of "self" meant that any changes to that data were limited to the scope of the method in that particular class (and it's resultant object), thereby insulating it from other methods in the same class and other objects which inherit from the same class" (Don't reply to this yet! :-)
I'm sure that I have simply thought that my global declaration was not going to be changed in place by misunderstanding what "self" means. My confusion stemmed from just how weird the change appeard to be. I.e. "But I just looked at the dang thing and it was what I expected! Where dem extra parentheis come from? Huh?"
I apologize for my incoherence in asking the question. I was in the middle of trying out different ideas and ran onto this weirdness and could not let it go. I should taken the time to write a generic example, but frankly, I was frustrated and was not thinking about how best to frame the question. It was impolite of me to subject the list to my half-baked meanderings. Again, sorry. You guys have helped so much and you deserve a little more effort on my part.
So, fortified with 8 hours of sleep and 15mg of Adderall, here we go!
Classes are used to generate objects. Objects represent things.
By logical deduction objects correspond to nouns in language.
Objects do things when they receive messages (Possibly
from other objects). Messages cause methods to be invoked,
methods therefore correspond to verbs in language.
I felt like I was being told an integer is a "counting number" here. ;-)
Looking at your code we find:
class Create: # a verb
def freshDB(self, DBPATH, Fields): # a noun
def comparisonTable(self, DBPATH, Fields, columns, mode): #a noun
In other words you have the concept inside out.
you are trying to create Create objects and call Table and Database
methods. It doesn't make sense.
Normally we would expect to see DB and Table objects to which
you send create messages.
I was even more confused. Were you objecting to my nomenclature?
So I thought, "If I named the class "Steve" and called the methods createFreshDB() and createComparisonTable() so it would read:
"Steve, create a fresh database which includes tables named for the keys and columns named for the values in this dictionary I'm handing you."
"Steve, create a comparison table just like above, but with a different key."
which would be followed (eventually, if I hadn't gotten bogged down) by
"Steve, tell gadfly to collate those two tables I just had you make and put them in another table so I can generate a report"
Would that make any difference?
No especially in how the code was written (it was still ugly and half-baked, and showing tons of bad habits), but I did suddenly realize what you meant by "noun".
I have been treating objects like a corporate sales droid treats nouns.
I've been "Gifting" and "Tableing" the objects "TheGift" and "TheTable" in my mind. (I fear I've also been "Impacting" the method "impact()" without asking Steve.Please() first, (I.E. not quite understanding why my classes within the modules were not showing up like I expected, but that's another story.)
I've not been thinking of an object as a verb, rather more like a gerund. Still wrong, but a different kind of wrong.
Now if you think of the objects as verbs then self is a confusing
concept.
But if you think of the objects as nouns then self is simply a
reference
to the object instance in question, a particular database or table.
Which leads me back to the "why is it there?" question I saw on the list recently.
If "self" is simply a reference to the object instance in
question, then why does one have to basically mirror the variable at
the top of the class?
The example I was working from is at: http://www.penzilla.net/tutorials/python/modules/
This seems bizzare and redundant, but I did it anyway, all the time thinking, "Why not just clone the variable, I.E. 'titleForMyPurposesHereInThisInstance = title'? "
Does it follow that if one does not prepend "self" to the variable, any change will affect all instances of an object (say in a threading situation)? That is the only thing that seems to make sense to me, otherwise "self" would just be silly.
The example I was working from is at: http://www.penzilla.net/tutorials/python/modules/
# Intro To Python: Modules
# book.py
"""
Class: Book( title, author, keywords )
Each book object takes a title, optional author, and optional keywords.
"""
class Book:
def
__init__(self, title, author="Unknown", keywords=[]):
"""
Books take three arguments to their constructor
The first and only required argument is the title,
followed by the optional arguments, author, and a list
of keywords that can be used to look up a specific book.
"""
self.title = title
self.author = author
self.keywords = keywords
def setTitle
(self, title):
This seems bizzare and redundant, but I did it anyway, all the time thinking, "Why not just clone the variable, I.E. 'titleForMyPurposesHereInThisInstance = title'? "
Does it follow that if one does not prepend "self" to the variable, any change will affect all instances of an object (say in a threading situation)? That is the only thing that seems to make sense to me, otherwise "self" would just be silly.
I'd recommend going back and rethinking the design of your
objects before going much further.
As I said, all that stuff was throwaway anyway and I should have made a more generic example.
Thanks!
HTH,
--
Alan Gauld
Author of the Learn to Program web site
http://www.freenetpages.co.uk/hp/alan.gauld
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