update_idletasks difficulty in python tkinter

Question

I'm having trouble calling .update_idletasks() to redraw my canvas ( at the end of the .set_up() Class-method ).

If I use self.canv.update_idletasks( self ) , the canvas draws the objects I want but gives the error

TypeError: update_idletasks() takes exactly 1 argument (2 given)

If I use self.canv.update_idletasks() , the canvas remains blank but doesn't produce any errors.

from Tkinter import *


class Animation(Frame):

def __init__(self,parent=None):
    Frame.__init__(self,parent)
    self.pack()
    self.generation = 1
    self.epoch = 1
    self.set_up()

def set_up(self):
    greeting_text = 'Generation ' + str(self.generation) + ', Epoch ' + str(self.epoch)
    header = Label(self,text=greeting_text)
    header.pack()

    anframe = Frame(self,relief=SUNKEN)
    anframe.pack(side='left',padx=10,pady=10)
    self.canv = Canvas(anframe,width=800, height=800, bg='white')   # 0,0 is top left corner
    self.canv.pack(expand=YES, fill=BOTH,side='left')

    buframe = Frame(self,relief=RAISED)
    buframe.pack(side='right',fill=X,padx=10,pady=5)

    start = Button(buframe,text='START',width=10,command=self.animate)
    start.pack(expand=YES,fill=BOTH,side='top')
    back  = Button(buframe,text='Back',width=10)
    back.pack(expand=YES,fill=BOTH,side='bottom')
    nextgo= Button(buframe,text='Next',width=10)
    nextgo.pack(expand=YES,fill=BOTH,side='bottom')

    path = 'C:/Desktop/LearnNet/' + str(self.generation) + '_' + str(self.epoch) + '.txt'
    data = open(path,'r')
    lines = data.readlines()

    food,moves = [],[]
    for item in lines:
        if item.strip() == 'f':
            dat_type = 1
            continue
        elif item.strip() == 'a':
            dat_type = 2
            continue

        if dat_type == 1:
            temp = item.strip()
            temp = item.split()
            food.append([int(temp[0]),int(temp[1])])

        if dat_type == 2:
            temp = item.strip()
            temp = item.split()
            moves.append([int(temp[0]),int(temp[1]),int(temp[2])])

    photos = []
    for i in xrange(len(food)):
        temp=PhotoImage(file='C:/Desktop/LearnNet/Food.gif')
        photos.append(temp)
        self.canv.create_image(food[i][0]*20,food[i][1]*20,image=photos[i],anchor=NW)

    start_pos = moves[0]
    picpath = self.orientation(start_pos[2])
    animal = PhotoImage(file=picpath)

    self.canv.create_image(moves[0][0]*20,moves[0][1]*20,image=animal,anchor=NW)
    self.canv.update_idletasks(self)

def animate(self):
    return 1
def orientation(self,angle):
    if angle == 0:
        picpath = 'C:/Desktop/LearnNet/PEast.gif'
    elif angle == 90:
        picpath = 'C:/Desktop/LearnNet/PNorth.gif'
    elif angle == 180:
        picpath = 'C:/Desktop/LearnNet/PWest.gif'
    else:
        picpath = 'C:/Desktop/LearnNet/PSouth.gif'

    return picpath
if __name__ == '__main__': Animation().mainloop()

Answer 1

self in python is actually syntactic sugar.

In other words, when you say self.animate() , python translates it to Animation.animate(self) . That's why you define the class methods with that "self" argument -- it's passed implicitly.

self.canv.update_idletasks(self) is evaluating to something like Canvas.update_idletasks(self.canv, self) .

Answer 2

I found a solution by looking at some similar code. self.canv.get_tk_widgets().update_idletasks( ) does the trick, thought I am not quite sure WHY this works, If anyone could explain or point me to some reading. Thanks