Hi guys,I've a problem with selecting an item from a listbox,could anyone tell me why the following does not work?
from Tkinter import *
root=Tk()
frame=Frame(root)
frame.pack()
listbox=Listbox(frame)
list=["fred","joe","green"]
for item in list:
listbox.insert(END,item)
listbox.pack(frame)
list=listbox.curselection()
def printitem(list):
print item
listbox.bind("<Button-1>",printitem)

nevle

: Hi guys,I've a problem with selecting an item from a listbox,could anyone tell me why the following does not work?
: from Tkinter import *
: root=Tk()
: frame=Frame(root)
: frame.pack()
: listbox=Listbox(frame)
: list=["fred","joe","green"]
: for item in list:
: listbox.insert(END,item)
: listbox.pack(frame)
: list=listbox.curselection()
: def printitem(list):
: print item
: listbox.bind("<Button-1>",printitem)

I tinkered with this a little to see what I could figure out without searching the docs, and it appears that functions bound to an event are sent one argument, the event itself. As you've defined "printitem" here, the "list" argument is actually holding an event object. Not only that, but the body of the function refers to "item" which is never set anywhere. Here's what I did:

>>> from Tkinter import *
>>> root = Tk()
>>> frame = Frame(root)
>>> frame.pack()
>>> listbox = Listbox(frame)
>>> listbox.insert(END, "FRED")
>>> listbox.insert(END, "JOE")
>>> listbox.insert(END, "GREEN")
>>> listbox.pack(frame)
>>> def printitem(event):
... 	print listbox.get(listbox.curselection())
... 	
>>> listbox.bind("<Button-1>",printitem)
'17904112printitem'
>>> root.mainloop()
Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Python22\lib\lib-tk\Tkinter.py", line 1300, in __call__
    return apply(self.func, args)
  File "<interactive input>", line 2, in printitem
  File "C:\Python22\lib\lib-tk\Tkinter.py", line 2304, in get
    return self.tk.call(self._w, 'get', first)
TclError: bad listbox index "": must be active, anchor, end, @x,y, or a number
FRED
JOE
JOE
GREEN
GREEN
GREEN
GREEN
GREEN
JOE
JOE
FRED
FRED

For some reason it prints out the item I was on before the button was clicked. That's why there's that exception in there, there was no selected item before the first click. That seems odd to me, but there must be a reasonable explanation for it. Check the documentation and let us know what you find.


infidel

: I tinkered with this a little to see what I could figure out without searching the docs, and it appears that functions bound to an event are sent one argument, the event itself. As you've defined "printitem" here, the "list" argument is actually holding an event object. Not only that, but the body of the function refers to "item" which is never set anywhere. Here's what I did:
:
:

: >>> from Tkinter import *
: >>> root = Tk()
: >>> frame = Frame(root)
: >>> frame.pack()
: >>> listbox = Listbox(frame)
: >>> listbox.insert(END, "FRED")
: >>> listbox.insert(END, "JOE")
: >>> listbox.insert(END, "GREEN")
: >>> listbox.pack(frame)
: >>> def printitem(event):
: ... 	print listbox.get(listbox.curselection())
: ... 	
: >>> listbox.bind("<Button-1>",printitem)
: '17904112printitem'
: >>> root.mainloop()
: Exception in Tkinter callback
: Traceback (most recent call last):
:   File "C:\Python22\lib\lib-tk\Tkinter.py", line 1300, in __call__
:     return apply(self.func, args)
:   File "<interactive input>", line 2, in printitem
:   File "C:\Python22\lib\lib-tk\Tkinter.py", line 2304, in get
:     return self.tk.call(self._w, 'get', first)
: TclError: bad listbox index "": must be active, anchor, end, @x,y, or a number
: FRED
: JOE
: JOE
: GREEN
: GREEN
: GREEN
: GREEN
: GREEN
: JOE
: JOE
: FRED
: FRED
: 

:
: For some reason it prints out the item I was on before the button was clicked. That's why there's that exception in there, there was no selected item before the first click. That seems odd to me, but there must be a reasonable explanation for it. Check the documentation and let us know what you find.


Hi infidel,I couldn't find out much from the documentation that I have here (still that's not surprising,I only understand a very small fraction of it so far)however,if you "double-button-1" it works properly??
Also adding "listbox.select_set(0) / listbox.see(0)" sets the curser on whichever item you choose to start at(and never end a sentence with a preposition).
thanks


nevle