[Tutor] Function assignment (was: Re: Function type?)

[Jeff Shannon]

A few points...

># Function Description
>
>pipe = Item('pipe')
>def pipe_desc():
>    if self.parent = player:
>         return "In your hand."
>    return "On the floor."
>pipe.desc = pipe_desc
>

Actually, this will *not* work.  In your pipe_desc() function, you use 
'self' -- but there's nowhere for that self to come from!  You need to 
actually have self in the argument list, i.e. 'def pipe_desc(self): 
[...]'  However, there's still one more trick needed.  In order for 
'self' to be given the right value when called as a method, you have to 
tell Python that this is a method of your pipe object.  I believe that 
this can be done using the 'new' module's instancemethod() function.


>Which means there's this pipe_desc object floating around, and could
>accidentally be overwritten. So I have to force a naming convention, such
>as itemname_function. Which would work, but feels kludgy and isn't as
>elegant.
>

Actually, you don't need to worry about that.  As long as you still have 
a reference to the function object, the original reference can go away 
or be overwritten without harm.

 >>> def f():
...     print "I'm here!"
...    
 >>> f()
I'm here!
 >>> function = f
 >>> del f
 >>> f()
Traceback (most recent call last):
  File "<interactive input>", line 1, in ?
NameError: name 'f' is not defined
 >>> function()
I'm here!
 >>>

So once you've assigned your function to pipe.desc, pipe_desc isn't 
needed any more, and could even be re-used.  Be careful about re-using 
function names, though -- you need to be aware of when the def statement 
is executed.  You'd need to have the first function object assigned to a 
different name before the second def statement creates a new function 
object with the same name.  This is where something like makeMsg() is 
useful -- a new function is defined each time makeMsg() is called, and 
you must assign that function to a name in order to hold on to it, so it 
forces proper serialization of your function definitions.

Jeff Shannon
Technician/Programmer
Credit International