Unexpected behaviour with Python / Tkinter

amcleod · 07-16-2012, 10:05 PM

New to Python & Tkinter, so need some help.

When you do

Code:

Label( framename, ...)

Isn't the label supposed to appear inside the named frame? I'm running the following script:

Code:

#!/usr/bin/python

from Tkinter import *

# create toplevel container widget
root = Tk()
root.config( bg='blue' )

# create separate container frames for header line and three data lines
hdr = Frame( root, height=16, bg='yellow').pack(side=TOP, fill=X)
ln1 = Frame( root, height=16, bg='green').pack(side=TOP, fill=X)
ln2 = Frame( root, height=16, bg='pink').pack(side=TOP, fill=X)
ln3 = Frame( root, height=16, bg='orange').pack(side=TOP, fill=X)

d0 = Label( hdr,  bg='cyan', width=10, text='DATE' ).pack( side=LEFT )
d1 = Label( ln1, bg='gray', width=10, text='2007-06-13' ).pack( side=LEFT )
d2 = Label( ln2, bg='cyan', width=10, text='2012-04-09' ).pack( side=LEFT )
d3 = Label( ln3, bg='gray', width=10, text='1997-11-27' ).pack( side=LEFT )

t0 = Label( hdr, bg='magenta', width=6, text='TIME' ).pack( side=LEFT )
t1 = Label( ln1, bg='purple', width=6, text='12:45' ).pack( side=LEFT )
t2 = Label( ln2, bg='magenta', width=6, text='13:25' ).pack( side=LEFT )
t3 = Label( ln3, bg='purple', width=6, text='11:06' ).pack( side=LEFT )

root.mainloop()

Labels aren't appearing inside container frames as I expect, but are inside the root frame after the container frames. Am I mistaken in thinking that a label should appear inside it's parent? If so, how do I get a label to appear inside a particular frame of choice? (Weird set of colours solely so I can see what ends up where.)

amcleod · 07-17-2012, 10:36 AM

In comparison, this script:

Code:

#!/usr/local/bin/perl -w

use Tk;

$root = new MainWindow( -bg => 'blue' );

$hdr = $root->Frame( -height=>16, -bg=>'yellow' )->pack( -side=>'top', -fill=>'x' );
$ln1 = $root->Frame( -height=>16, -bg=>'green' )->pack( -side=>'top', -fill=>'x' );
$ln2 = $root->Frame( -height=>16, -bg=>'pink' )->pack( -side=>'top', -fill=>'x' );
$ln3 = $root->Frame( -height=>16, -bg=>'orange' )->pack( -side=>'top', -fill=>'x' );

$d0 = $hdr->Label( -bg=>'cyan', -width=>10, -text=>'DATE' )->pack( -side=>'left' );
$d1 = $ln1->Label( -bg=>'gray', -width=>10, -text=>'2007-06-13' )->pack( -side=>'left' );
$d2 = $ln2->Label( -bg=>'cyan', -width=>10, -text=>'2012-04-09' )->pack( -side=>'left' );
$d3 = $ln3->Label( -bg=>'gray', -width=>10, -text=>'1997-11-27' )->pack( -side=>'left' );

$t0 = $hdr->Label( -bg=>'magenta', -width=>6, -text=>'TIME' )->pack( -side=>'left' );
$t1 = $ln1->Label( -bg=>'purple', -width=>6, -text=>'12:45' )->pack( -side=>'left' );
$t2 = $ln2->Label( -bg=>'magenta', -width=>6, -text=>'13:25' )->pack( -side=>'left' );
$t3 = $ln3->Label( -bg=>'purple', -width=>6, -text=>'11:06' )->pack( -side=>'left' );

MainLoop;

behaves just as I would have expected.

audriusk · 07-17-2012, 01:43 PM

This is because when you instantiate Frame class like this

Code:

hdr = Frame(root, height=16, bg='yellow').pack(side=TOP, fill=X)

first you get its instance, but the instance method pack(), which is called immediately, doesn't return the instance itself. In Python functions, that don't have return statement, return None. So, your hdr variable ends up refering to None. Here's what you should do instead:

Code:

hdr = Frame(root, height=16, bg='yellow')
hdr.pack(side=TOP, fill=X)

amcleod · 07-17-2012, 11:15 PM

Thanks! With your suggested changes, everything now works as expected. I appreciate your taking the time to explain.