[Tutor] methods and functions

[Lloyd Kvam]

printIt is a method.  name is an attribute of class A instances.
 >>> a.name(b)
Traceback (most recent call last):
   File "<interactive input>", line 1, in ?
TypeError: 'str' object is not callable

We can try this:
 >>> a.name = b
 >>> a.printIt()
<__main__.B instance at 0x013B0EA0>

The name attribute of a is no longer a string.  When python
tries to print it, it uses its default machinary to turn that
instance of the B class into a string and then prints the
result.

PrintIt could be written as a regular old function outside the class.
def printIt(arg):
     print arg.name
I changed self to arg simply because there is no longer a self concept.  self
would still be valid Python syntax.

 >>> a=A('Aay')
 >>> printIt(a)
Aay

 >>> printIt(b)
Traceback (most recent call last):
   File "<interactive input>", line 1, in ?
   File "E:\ptg\campgrnd\Script1.py", line 13, in printIt
     print arg.name
AttributeError: B instance has no attribute 'name'

the class A __init__ provided a name attribute for each instance.  The B
instances are missing that attribute.  So printIt is only usefule when it's
argument has a name attribute.  Keeping printIt part of the A class makes
it difficult to pass in an argument that will not work.

HTH

Gerardo Arnaez wrote:
> --- Lloyd Kvam <pythontutor@venix.com> wrote:
>   A method is essentially a function
> 
>>defined within a class body.
> 
> 
> Than is an instance method just passing an some other
> class instace thorught another class instances' method
> 
> ie 
> 
> class A:
>    def __init__ (self,A):
>       self.name=A
> 
>    def printIt(self):
>       print self.name
> 
> class B:
>    def __init__ (self):
>       pass
> 
> 
> a=A('Aay')
> b=B()
> 
> a.name
> 'Aay'
> 
> a.printIt
> 'Aay'
> 
> So what does
> 
> a.name(b) do?
> Is this an instance method?
> 
> Is how a method differs from a function?
> 
> 
> G
> 
> 
> 
> 
> 
> 
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-- 
Lloyd Kvam
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