[Tutor] Simple Question On A Method (in subclass)

[Chris Kavanagh]

On 10/23/2011 6:22 PM, Dave Angel wrote:
>
> (please do REPLY-ALL, or at least add the mailing list to the recipient
> list. Otherwise, only one person will see the message. I'm forwarding it
> to the group with my comments added.)
>
> -------- Original Message --------
> Subject: Re: [Tutor] Simple Question On A Method (in subclass)
> Date: Sun, 23 Oct 2011 16:53:40 -0400
> From: Chris Kavanagh <ckava1 at msn.com>
> Organization: Home Office
> To: d at davea.name
>
>
>
> On 10/22/2011 6:59 PM, Dave Angel wrote:
>>
>>> My question is regarding the tell methods in the subclasses,the code
>>> {SchoolMember.tell(self)}, in the class Teacher & Student. I just
>>> don't understand what this is doing? Calling the first method {def
>>> tell} from the parent class, I assume? There is already a print
>>> statement in each of the subclass {def tell} showing details, why call
>>> another print statement (from parent class {def tell})?? I know this
>>> should be simple, but I'm confused. LOL, obviously.
>>>
>>> Thank you in advance!
>>>
>>>
>>> <SNIP>
>
>> Welcome to the python-tutor list. We are all volunteers here, and most,
>> like me, ask questions as well as answering them. it's a two-way street.
>>
>> The whole point of subclassing is to share either code, data, or both.
>> In this example, the amount of shared data is just the name and age, and
>> the shared method is tell(). Because the parent knows how to 'tell' its
>> information, the child doesn't need to. So instead of altering the
>> prints in both the child classes to print name & age, you let the common
>> code in the parent handle it.
>>
>> It becomes more clearly a win when you have much more data, or much more
>> complex methods involved. But you have to start simple.
>>
>> BTW, there were some transcription errors in the email. For example, the
>> code as written would be using a separate line for Salary on Mrs.
>> Shrividya's record. And you're missing the content of the for member in
>> members: loop. No problem, but it might have affected our discussion.
>> Did you retype it all, or was it just a glitch? Presumably you know how
>> to copy/paste from and to a console prompt?
>
> Chris Kavanagh said:
>
> Thanks to both Alan Gauld & Dave Angel for the help!!!
>
> I'm not sure how the transcrption errors happened, I copied & pasted.
> Must have not copied the entire thing. I'll correct it below.
>
> Speaking of the last line of code, I have a question about that also.
> The last line should have been (without my error) {member.tell()}.
> My question is, why couldn't this last line have been {print member}??
> Every example of an iterator I've seen until this point of my learning,
> has had a print statement then the item variable. Instead, Swaroop uses
> the item variable to call the function {tell()}. This is sorta confusing
> to me. What if there was no function to print out the Student and
> Teacher variable?? How would the iterator been printed out in that
> case?? Thanks again, in advance. Here's the correct code.
>
>
> class SchoolMember:
> '''Represents any school member.'''
> def __init__(self, name, age):
> self.name = name
> self.age = age
> print '(Initialized SchoolMember: %s)' % self.name
>
> def tell(self):
> '''Tell my details.'''
> print 'Name:"%s" Age:"%s"' % (self.name, self.age),
>
> class Teacher(SchoolMember):
> '''Represents a teacher.'''
> def __init__(self, name, age, salary):
> SchoolMember.__init__(self, name, age)
> self.salary = salary
> print '(Initialized Teacher: %s)' % self.name
>
> def tell(self):
> SchoolMember.tell(self)
> print 'Salary: "%d"' % self.salary
>
> class Student(SchoolMember):
> '''Represents a student.'''
> def __init__(self, name, age, marks):
> SchoolMember.__init__(self, name, age)
> self.marks = marks
> print '(Initialized Student: %s)' % self.name
>
> def tell(self):
> SchoolMember.tell(self)
> print 'Marks: "%d"' % self.marks
>
> t = Teacher('Mrs. Shrividya', 40, 30000)
> s = Student('Swaroop', 22, 75)
>
> print # prints a blank line
>
> members = [t, s]
> for member in members:
> member.tell() # works for both Teachers and Students
>
>
>
> Output
>
>
> $ python inherit.py
> (Initialized SchoolMember: Mrs. Shrividya)
> (Initialized Teacher: Mrs. Shrividya)
> (Initialized SchoolMember: Swaroop)
> (Initialized Student: Swaroop)
>
> Name:"Mrs. Shrividya" Age:"40" Salary: "30000"
> Name:"Swaroop" Age:"22" Marks: "75"
>
>  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> You always have a choice of where to put useful code. if you put it in
> member functions, it can be shared by all the callers. There's no right
> or wrong way to do it. The only "rule" I can think of is not to mix
> significant calculations with prints. Make them two different methods,
> so the user of the class can use them independently.
>
> If you had no class member like tell(), one choice would be to enumerate
> the members yourself. So you could do something like:
>
> print member.name, member.age, member.marks, member.salary
>
> With some formatting. But not all members have all these fields, so
> you'd have to do some conditional testing, and it could get quite complex.
>
> --
>
> DaveA
>
>
>
>
>
>
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>
Sorry, thought I hit reply all. . .I'm still a little shaky on this. I 
thought if you created an iterator, and you wanted to see the results, 
you had to write, print(item variable). How can you use the item 
variable with a function? Is it because the item variable, in this case 
{member}, is an object? And because it's an object you can use dot 
notation to call the {tell} function {member.tell()}

Sorry for the confusing question. Sometimes I'm not quite sure how to 
ask what I want to know, lol. . .Anyways, THANKS so much for the help.