(help)Tkinter, how to make labels scrolling?

[Francesco Bochicchio]

On 28 Dic, 09:44, Ren Wenshan <renws1... at gmail.com> wrote:
> Hi, everyone:
>
>    I am new to programming and Python and these days I've been working
> on a
> tiny program for practice and encountered with a problem.
>
>    My tiny program read a line from a data file one time, and store it
> in a list, till the list is full. This is the init.
>    Then when I press Button Start, I want the program will read a
> line,
> list.pop(0) list.append(line) in a loop. Thus, make the labels
> scrolling.
>    English is not my mother tongue, I hope I've made myself
> understood.
>
>    the whole source code:
>
> from Tkinter import *
> import sys
> import time
>
> # position of buttons
> row_button = 5
> col_button = 4
>
> # font size
> size_title = 20
> size_button = 12
> size_text = 14
>
> # the length of name_list
> Len_List = 3
>
> class meal( Frame ):
>
>     def __init__(self):
>         Frame.__init__(self)
>         self.pack( expand = YES, fill = BOTH)
>         self.master.title("Languages")
>
>         self.label_1 = Label(self, text = "Too many languages to
> choose...", font = ("arial", size_title))
>         self.label_2 = Label(self, text = "Which is the Lucky one",
> font = ("arial", size_title-4))
>         self.label_1.grid(row = 0, column = 0)
>         self.label_2.grid(row = 1, column = 2)
>
>         self.button_start = Button(self, text = "start", font =
> ("arial", size_button), command = self.start)
>         self.button_stop = Button(self, text = "stop", font =
> ("arial", size_button))
>         self.button_quit = Button(self, text = "quit", font =
> ("arial", size_button), command = self.quit)
>
>         self.button_start.grid(row = row_button, column = col_button)
>         self.button_stop.grid(row = row_button, column = col_button+1)
>         self.button_quit.grid(row = row_button,column = col_button+2)
>
>         self.name_list = [None] * Len_List
>         self.label_list = [None] * Len_List
>
>         self.fp = open("data.txt", 'r')
>         for i in range(Len_List):
>             self.name_list[i] = self.fp.readline()
>         for i in range(Len_List):
>             self.label_list[i] = Label(self, text = self.name_list[i],
> font = ("arial", 12))
>             self.label_list[i].grid(row = 2+i, column = 2)
>
>     def start(self):
>         self.line = self.fp.readline()
>         if not self.line:
>             self.fp.seek(0)
>             self.line = self.fp.readline()
>         self.name_list.pop(0)
>         self.name_list.append(self.line)
>
>         for i in range(Len_List):
>             self.label_list[i].destroy()
>             self.label_list[i] = Label(self, text = self.name_list[i],
> font = ("arial", 12))
>             self.label_list[i].grid(row = 2+i, column = 2)
>
>     def quit(self):
>         sys.exit(0)
>
> app = meal()
> app.mainloop()
>
> Best wishes
>
> Vincent Ren

Hi,

if you want to realize an 'animated scrolling' effect, you need to
move the scrolling code out of the start callback
in a function which is called periodically by the GUI mainloop. In
Tkinter, you can do that using Toplevel.after to
have a fuction be called after a timeout. Here is your 'meal' class
with the modifications needed to make an
'animated scroll'. I renamed your start method as _scroll_text and
wrote  new start and stop methods to start and stop
the scrolling.

Ciao
-----
FB


lass meal( Frame ):
    SCROLL_DELAY = 500 # milliseconds
    def __init__(self):
        Frame.__init__(self)
        self.pack( expand = YES, fill = BOTH)
        self.master.title("Languages")

        self.label_1 = Label(self, text = "Too many languages to
choose...", font = ("arial", size_title))
        self.label_2 = Label(self, text = "Which is the Lucky one",
font = ("arial", size_title-4))
        self.label_1.grid(row = 0, column = 0)
        self.label_2.grid(row = 1, column = 2)

        self.button_start = Button(self, text = "start", font =
("arial", size_button), command = self.start)
        self.button_stop = Button(self, text = "stop", font =
("arial", size_button), command = self.stop )
        self.button_quit = Button(self, text = "quit", font =
("arial", size_button), command = self.quit)

        self.button_start.grid(row = row_button, column = col_button)
        self.button_stop.grid(row = row_button, column = col_button+1)
        self.button_quit.grid(row = row_button,column = col_button+2)

        self.name_list = [None] * Len_List
        self.label_list = [None] * Len_List

        self.fp = open("data.txt", 'r')
        for i in range(Len_List):
            self.name_list[i] = self.fp.readline()
        for i in range(Len_List):
            self.label_list[i] = Label(self, text = self.name_list[i],
font = ("arial", 12))
            self.label_list[i].grid(row = 2+i, column = 2)

        self.after_id = None

    def _scroll_text(self):
        #print "_scroll_text"
        self.line = self.fp.readline()
        if not self.line:
            self.fp.seek(0)
            self.line = self.fp.readline()
        self.name_list.pop(0)
        self.name_list.append(self.line)

        for i in range(Len_List):
            self.label_list[i].destroy()
            self.label_list[i] = Label(self, text = self.name_list[i],
font = ("arial", 12))
            self.label_list[i].grid(row = 2+i, column = 2)
        self.after_id = self.master.after(self.SCROLL_DELAY,
self._scroll_text)

    def start(self):
        self.after_id = self.master.after(self.SCROLL_DELAY,
self._scroll_text)

    def stop(self):
        if self.after_id:
            self.master.after_cancel(self.after_id)
            self.after_id = None

    def quit(self):
        sys.exit(0)