[Tkinter-discuss] return value in event handler

[Alexander Belchenko]

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I saw recipe in Python Cookbook about multilistbox implementation.
(see code below). I try to understand why for event handlers
have return value 'break'.

E.g., shortest example:

            lb.bind('<Leave>', lambda e: 'break')

Does this mean something special?
What other possible values exists?


The code from recipe:

from Tkinter import *

class MultiListbox(Frame):
    def __init__(self, master, lists):
        Frame.__init__(self, master)
        self.lists = []
        for l,w in lists:
            frame = Frame(self); frame.pack(side=LEFT, expand=YES, fill=BOTH)
            Label(frame, text=l, borderwidth=1, relief=RAISED).pack(fill=X)
            lb = Listbox(frame, width=w, borderwidth=0, selectborderwidth=0,
                         relief=FLAT, exportselection=FALSE)
            lb.pack(expand=YES, fill=BOTH)
            self.lists.append(lb)
            lb.bind('<B1-Motion>', lambda e, s=self: s._select(e.y))
            lb.bind('<Button-1>', lambda e, s=self: s._select(e.y))
            lb.bind('<Leave>', lambda e: 'break')
            lb.bind('<B2-Motion>', lambda e, s=self: s._b2motion(e.x, e.y))
            lb.bind('<Button-2>', lambda e, s=self: s._button2(e.x, e.y))
        frame = Frame(self); frame.pack(side=LEFT, fill=Y)
        Label(frame, borderwidth=1, relief=RAISED).pack(fill=X)
        sb = Scrollbar(frame, orient=VERTICAL, command=self._scroll)
        sb.pack(expand=YES, fill=Y)
        self.lists[0]['yscrollcommand']=sb.set

    def _select(self, y):
        row = self.lists[0].nearest(y)
        self.selection_clear(0, END)
        self.selection_set(row)
        return 'break'

    def _button2(self, x, y):
        for l in self.lists: l.scan_mark(x, y)
        return 'break'

    def _b2motion(self, x, y):
        for l in self.lists: l.scan_dragto(x, y)
        return 'break'

    def _scroll(self, *args):
        for l in self.lists:
            apply(l.yview, args)

    def curselection(self):
        return self.lists[0].curselection()

    def delete(self, first, last=None):
        for l in self.lists:
            l.delete(first, last)

    def get(self, first, last=None):
        result = []
        for l in self.lists:
            result.append(l.get(first,last))
        if last: return apply(map, [None] + result)
        return result

    def index(self, index):
        self.lists[0].index(index)

    def insert(self, index, *elements):
        for e in elements:
            i = 0
            for l in self.lists:
                l.insert(index, e[i])
                i = i + 1

    def size(self):
        return self.lists[0].size()

    def see(self, index):
        for l in self.lists:
            l.see(index)

    def selection_anchor(self, index):
        for l in self.lists:
            l.selection_anchor(index)

    def selection_clear(self, first, last=None):
        for l in self.lists:
            l.selection_clear(first, last)

    def selection_includes(self, index):
        return self.lists[0].selection_includes(index)

    def selection_set(self, first, last=None):
        for l in self.lists:
            l.selection_set(first, last)

if __name__ == '__main__':
    tk = Tk()
    Label(tk, text='MultiListbox').pack()
    mlb = MultiListbox(tk, (('Subject', 40), ('Sender', 20), ('Date', 10)))
    for i in range(1000):
        mlb.insert(END, ('Important Message: %d' % i, 'John Doe', '10/10/%04d' % (1900+i)))
    mlb.pack(expand=YES,fill=BOTH)
    tk.mainloop()




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