Little help with exercise 41

[divyang_patel]

@nellietobey

A class is just a Tupperware container who’s label can stick to everything inside.
The instance is just the copy of that container the compiler can take off the shelf, open up and use what’s inside.

yes this terms are now very clear

@nellietobey

An instance doesn’t have to have any parameters.
The base class doesn’t either.
Initiating parameters is optional.

i think as i continue this book this thing will become clear

@nellietobey

I’m not sure if using so many words to describe it is necessary. Just play with the code, make it do tricks, you’ll see.

yes i am bit focusing on theory and terms because without knowing what is happening behind the scene does not giving me confidence to practice EX41 and to move on with book
i think what was main obstacle is confusion between instance and object which is now clear
can you do me a one last favor
read this post in which i asked question about calling a class by two different ways

@divyang_patel

as you said to run above code, i did that in two way
one as @io_io you said foo = A
and second as @zedshaw shown in EX40 like calling a class like function foo = A()
i have changed your code a bit

class A(object):
    def __init__(self):
        self.K = "bjgrft"
        print("self = ",self)
foo = A
print("foo = ",foo)
print("A = ",A)

Q = "whatever"
print("Q = ",Q)

#print("foo.K = ",foo.K)

foo.K  = Q
print("foo = ",foo)
print("foo.K = ",foo.K)
print("Q = ",Q)

print("foo.K == 'whatever'",foo.K == "whatever")

output of this is

if i don’t comment line 12 which is [print("foo.K = ",foo.K)] then i got error which is

AttributeError: type object 'A' has no attribute 'K'

and by second way calling class like function

class A(object):
    def __init__(self):
        self.K = "bjgrft"
        print("self = ",self)
foo = A()
print("foo = ",foo)
print("A = ",A)

Q = "whatever"
print("Q = ",Q)

print("foo.K = ",foo.K)

foo.K  = Q
print("foo = ",foo)
print("foo.K = ",foo.K)
print("Q = ",Q)

print("foo.K == 'whatever'",foo.K == "whatever")

i got output like

can you explain difference between two ways
in second way i have not put comment on line 12 as before
and the difference i’m seeing in both way is

• self is printed in second way, not in first way
• getting an memory location of object foo in second way
• in first way i can’t fetch value of K which is on line 12, in second way i can fetch the K

[ulfen69]

Hello @divyang_patel.

Check out this and other videos from this guy. John Philip Jones
It helped me much when I first tried to understand classes.

[nellietobey]

I know you want to get all the theory language down, but honest, go play with the code so you can see it in action…
The first version is assigning that class, my blueprint to ‘foo’. It is not an instance – active usable copy of the class.
The second version is the instance being assigned to ‘foo’.

1. Make a simple class with simple attributes.
2. Try to get those values of those attributes and print them.
3. Try to assign new values to those attributes of that simple class.
   Look at your results…
   Then:
4. Make an instance of that simple classs
5. repeat steps 1 - 3.

there are class’s in the python language we use all the time without knowing it.
what would happen if someone could accidently or purposely change the class code?
This is a big reason the only way to use a class is to have an active copy of it, and NOT the class (and it’s original code) itself.

[divyang_patel]

oh so
in first version init does not run so instance is not created and zed said that self is a variable for the instance/object being accessed so there is no instance/object so self is not going to refer anything so that’s why we can’t access K
in second version instance is created and assigned to foo so self can refer to object foo so we can access K

• Make a simple class with simple attributes.
• Try to get those values of those attributes and print them.
• Try to assign new values to those attributes of that simple class.
  Look at your results…
  Then:
• Make an instance of that simple classs
• repeat steps 1 - 3.

yes i’m going to make some and practice this

[nellietobey]

All the theory in the human realm can’t replace experience.
You got this.