[Tutor] Re: Tutor digest, Vol 1 #1738 - 10 msgs

[Charlie Clark]

On 2002-07-04 at 19:55:02 [+0000], you wrote:
> class Beeper(Tkinter.Tk):
>   def __init__(self):
>     Tkinter.Tk.__init__(self)
>     Tkinter.Button(self, text=3D"Beep",
>       command=3Dself.beep).pack()
>     Tkinter.Button(self, text=3D"Quit",
>       command=3Dself.quit).pack()
> 
>   def beep(self):
>     print "Beep"
> 
> if __name__=3D=3D"__main__":
>   b =3D Beeper()
>   b.mainloop()
> 
> 
> Why has my Beeper instance no attribute 'beep' ??

Well, I think there are two things wrong but the error message is a 
standard Python gotcha: you are calling beep() before you have assigned it. 
But even if you define beep earlier I think you have a problem by calling a 
method as if it were an attribute.
self.beep is an attribute
beep(self) is a method and is directly accessible from within instances of 
the class even if the calls look the same from outside

a = Beeper()
a.beep
a.beep()

I'm not an expert on these things so I don't know what the real 
consequences of this are but look at the following:
>>> class Charlie:
...     def __init_(self):
...             self.beep = "BeeeP"
...     def beep(self):
...             print "Beep!" 
>>> a = Charlie
>>> a.beep
<unbound method Charlie.beep>
>>> a.beep()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: unbound method beep() must be called with instance as first 
argument

Common sense says your naming convention is likely to cause confusion.

Charlie