[Tutor] Self

[Gregor Lingl]

Ryan Sheehy schrieb:

>Thanks Todd and Danny!
>
>Danny:
>
>Okay... 'self' is required if calls need to be made to methods and functions
>that reside in the same class. Is that right?
>
>If so, could the call 'Person.pat_head()' still give the same result in the
>play_game method?
>
>Thanks,
>  
>
Hi Ryan!

I'll try to elaborate a bit Danny's example. Suppose you have:

class Person:
    def __init__(self, name):
        self.name = name
    def pat_head(self):
        print "I'm", self.name,"and",
        print "I'm patting my head"

    def rub_stomach(self):
        print "I'm", self.name, "and",
        print "I'm rubbing my stomach"

## The class Person can be used this way:

 >>> danny = Person("Danny")
 >>> ryan = Person("Ryan")
 >>> danny.rub_stomach()
I'm Danny and I'm rubbing my stomach
 >>> ryan.pat_head()
I'm Ryan and I'm patting my head

## We want Danny to play a game and define a function:

 >>> def play_game():
    danny.pat_head()
    danny.rub_stomach()
   
 >>> play_game()
I'm Danny and I'm patting my head
I'm Danny and I'm rubbing my stomach

## But what if Ryan also wants to play the game?
## We can redefine play_game with a parameter,
## so we can pass the person to play to it as
## an argument.

 >>> def play_game(somebody):
    somebody.pat_head()
    somebody.rub_stomach()

   
 >>> play_game(danny)
I'm Danny and I'm patting my head
I'm Danny and I'm rubbing my stomach
 >>> play_game(ryan)
I'm Ryan and I'm patting my head
I'm Ryan and I'm rubbing my stomach

## works fine. Now we can make this to
## a method of Person by simply putting it into the
class statement that defines Person:

class Person:
    def __init__(self, name):
        self.name = name
    def pat_head(self):
        print "I'm", self.name,"and",
        print "I'm patting my head"

    def rub_stomach(self):
        print "I'm", self.name, "and",
        print "I'm rubbing my stomach"
    def play_game(somebody):
        somebody.pat_head()
        somebody.rub_stomach()

## and try it out:

 >>> ================================ RESTART 
================================
 >>> danny = Person("Danny")
 >>> ryan = Person("Ryan")
 >>> danny.play_game()
I'm Danny and I'm patting my head
I'm Danny and I'm rubbing my stomach
 >>> ryan.play_game()
I'm Ryan and I'm patting my head
I'm Ryan and I'm rubbing my stomach

## works fine. Incidentally there is the *convention*
## to call the parameter that points to the object
## it*self* self.

## Alas, Your proposition to use Person.pat_head()
##  won't work, as it leaves open who should pat  his head.
##  But you *can* use a method like a function bound to a class,
##  passing the appropriate argument as earlier, like this:

 >>> Person.play_game(ryan)
I'm Ryan and I'm patting my head
I'm Ryan and I'm rubbing my stomach
 >>>

Hope this makes something more clear for you

Gregor