can someone explain why ..

[Schüle Daniel]

I don't understand what is the difference between commented lines
1 and 2

with 1 uncommented and 2 commented it works as expected
with 1 commented and 2 uncommented the picture doesn't appear

here is my code

#!/usr/bin/env python

from Tkinter import *
from Tkconstants import *

root = None

class Main:
def __init__(self):
global root
root = Tk(className = "Zeitrechne r")
root.config(bor derwidth = 5, relief = GROOVE)
root.geometry(" 0x0+100+50")

#self.im = image = PhotoImage(file = "./flower1.gif") #1
image = PhotoImage(file = "./flower1.gif") #2
frame1 = Frame(master = root, borderwidth = 3, relief = SUNKEN)
imageLabel = Label(master = frame1, image = image)

root.minsize(wi dth = image.width(), height = image.height())
root.maxsize(wi dth = 2*image.width() , height = image.height())

imageLabel.pack ()
frame1.pack(sid e = LEFT)

def mainloop(self):
root.mainloop()

main = Main()
main.mainloop()

[Farshid Lashkari]

Re: can someone explain why ..

Schüle Daniel wrote:[color=blue]
> I don't understand what is the difference between commented lines
> 1 and 2
>
> with 1 uncommented and 2 commented it works as expected
> with 1 commented and 2 uncommented the picture doesn't appear[/color]


I'm not familiar with Tkinter, but it seems as thought with 2, the
"image" variable is garbage collected after the constructor of Main is
called. With 1, you save a reference to the image, so it does not get
garbage collected.

-Farshid

[Schüle Daniel]

Re: can someone explain why ..

Farshid Lashkari schrieb:[color=blue]
> Schüle Daniel wrote:[color=green]
>> I don't understand what is the difference between commented lines
>> 1 and 2
>>
>> with 1 uncommented and 2 commented it works as expected
>> with 1 commented and 2 uncommented the picture doesn't appear[/color]
>
>
> I'm not familiar with Tkinter, but it seems as thought with 2, the
> "image" variable is garbage collected after the constructor of Main is
> called. With 1, you save a reference to the image, so it does not get
> garbage collected.[/color]

thx for quick reply :)

image is local variable of imageLabel
I would expect that in case imageLabel lives, it should
hold alife objects bound to its local variables

I am just curious *why* reference to image is not hold by imageLabel
which on his part is hold by frame1 .. which is hold by global root

Regards, Daniel

[Farshid Lashkari]

Re: can someone explain why ..

Schüle Daniel wrote:[color=blue]
> thx for quick reply :)
>
> image is local variable of imageLabel
> I would expect that in case imageLabel lives, it should
> hold alife objects bound to its local variables
>
> I am just curious *why* reference to image is not hold by imageLabel
> which on his part is hold by frame1 .. which is hold by global root[/color]

These are the only lines of code that reference "imageLabel ":

imageLabel = Label(master = frame1, image = image)
imageLabel.pack ()


Unless the constructor of Label adds a reference of itself to frame1,
imageLabel will also become garbage collected at the end of the
constructor. Are you sure this is the case?

-Farshid

[Schüle Daniel]

Re: can someone explain why ..

[..]
[color=blue]
> These are the only lines of code that reference "imageLabel ":
>
> imageLabel = Label(master = frame1, image = image)
> imageLabel.pack ()
>
>
> Unless the constructor of Label adds a reference of itself to frame1,
> imageLabel will also become garbage collected at the end of the
> constructor. Are you sure this is the case?[/color]

yes, now i see it
even can frame1 be dead after __init__
it binds itself too root with

frame1 = Frame(master = root)
frame1.pack(sid e = LEFT)

frame1.pack may append frame1 to root's list of all
widgets, we cannot see it, but it also may not do it

Thx

[Grant Edwards]

Re: can someone explain why ..

On 2006-04-25, Farshid Lashkari <lashkariNO@SPA Mworldviz.com> wrote:[color=blue]
> Schüle Daniel wrote:[color=green]
>> I don't understand what is the difference between commented lines
>> 1 and 2
>>
>> with 1 uncommented and 2 commented it works as expected
>> with 1 commented and 2 uncommented the picture doesn't appear[/color]
>
>
> I'm not familiar with Tkinter, but it seems as thought with 2, the
> "image" variable is garbage collected after the constructor of Main is
> called. With 1, you save a reference to the image, so it does not get
> garbage collected.[/color]

Yes. That's exactly correct. It's sort of a FAQ. See the
highlighted note at the bottom of

http://effbot.org/tkinterbook/bitmapimage.htm

--
Grant Edwards grante Yow! LOU GRANT froze
at my ASSETS!!
visi.com

[Grant Edwards]

Re: can someone explain why ..

On 2006-04-25, Schüle Daniel <uval@rz.uni-karlsruhe.de> wrote:
[color=blue][color=green]
>> I'm not familiar with Tkinter, but it seems as thought with 2,
>> the "image" variable is garbage collected after the
>> constructor of Main is called. With 1, you save a reference to
>> the image, so it does not get garbage collected.[/color][/color]

Correct.
[color=blue]
> image is local variable of imageLabel[/color]

Actually it's a parameter to the constructor that was called to
create the "imageLabel " object.
[color=blue]
> I would expect that in case imageLabel lives, it should hold
> alife objects bound to its local variables[/color]

It would. Therefore the "image" object apparently isn't bound
to a local variable in the object imageLabel.
[color=blue]
> I am just curious *why* reference to image is not hold by
> imageLabel which on his part is hold by frame1...[/color]

Good question. Untold millions of programmers have tripped
over that bug. Well, would you believe untold dozens? I know
I did. It's a common enough problem that it's given special
mention in a couple books on Tkinter.

My _guess_ is that this is one of the misfeatures resulting
from the way Tkinter is implimented: it's not a real binding of
Python to the tk library. It's a Python wrapper around a TCL
interpreter which is bound to the tk library (or something like
that). This results in some counter-intuitive (non-pythonic)
behaviors like the one you discovered with bitmap images and
labels.

--
Grant Edwards grante Yow! I feel like I'm
at in a Toilet Bowl with a
visi.com thumbtack in my forehead!!