global variables

[TheFlyingDutchman]

Does anyone know how the variables label and scale are recognized
without a global statement or parameter, in the function resize() in
this code:



#!/usr/bin/env python

from Tkinter import *

def resize(ev=None):
label.config(font='Helvetica -%d bold' % \
scale.get())


top = Tk()
top.geometry('250x150')

label = Label(top, text='Hello World!',
font='Helvetica -12 bold')
label.pack(fill=Y, expand=1)

scale = Scale(top, from_=10, to=40,
orient=HORIZONTAL, command=resize)
scale.set(12)
scale.pack(fill=X, expand=1)

quit = Button(top, text='QUIT',
command=top.quit, activeforeground='white',
activebackground='red')
quit.pack()

mainloop()

 

[Carsten Haese]

Does anyone know how the variables label and scale are recognized
without a global statement or parameter, in the function resize() in
this code:
[...]

The answer to your question is "Yes."

 

[Steven Bethard]

Does anyone know how the variables label and scale are recognized
without a global statement or parameter, in the function resize() in
this code: [snip]
def resize(ev=None):
label.config(font='Helvetica -%d bold' % \
scale.get())

You're just calling a method on the "label" object. Python looks in the
function local namespace and doesn't see a "label" object, so it steps
up to the global namespace. There is a "label" object in the global
namespace so it uses that one.

STeVe

 

[Erik Jones]

Does anyone know how the variables label and scale are recognized
without a global statement or parameter, in the function resize() in
this code:



#!/usr/bin/env python

from Tkinter import *

def resize(ev=None):
label.config(font='Helvetica -%d bold' % \
scale.get())


top = Tk()
top.geometry('250x150')

label = Label(top, text='Hello World!',
font='Helvetica -12 bold')
label.pack(fill=Y, expand=1)

scale = Scale(top, from_=10, to=40,
orient=HORIZONTAL, command=resize)
scale.set(12)
scale.pack(fill=X, expand=1)

quit = Button(top, text='QUIT',
command=top.quit, activeforeground='white',
activebackground='red')
quit.pack()

mainloop()

It's tricky. Basically, you only need to use the global statement if
you intend binding operations (assignments) on the variable name and
want those to affect the global variable. If you perform binding
operations without the global statement it is assumed that you are
defining a local variable.

class foo(object):
def foofoo(self):
print 7

def showfoo():
f.foofoo()

f = foo()
showfoo()
print f

outputs:

7
<__main__.foo object at ... >

with the same class:

def showfoo():
global f
f.foofoo()
f = 6

f = foo()
showfoo()
f
outputs:

7
6

with the same class again:

deff showfoo():
f.foofoo()
f = 6

f = foo()
showfoo()

outputs:

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 2, in showfoo
UnboundLocalError: local variable 'f' referenced before assignment

The difference in the last one is that when showfoo() is compiled the
assignment to f without any global statement makes f a local variable
and a method is called on it before it is bound which results in the
exception.

Erik Jones

Software Developer | Emma®
(e-mail address removed)
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[Colin J. Williams]

Does anyone know how the variables label and scale are recognized
without a global statement or parameter, in the function resize() in
this code:



#!/usr/bin/env python

from Tkinter import *

def resize(ev=None):
label.config(font='Helvetica -%d bold' % \
scale.get())


top = Tk()
top.geometry('250x150')

label = Label(top, text='Hello World!', <<<<<<
font='Helvetica -12 bold')
label.pack(fill=Y, expand=1)

scale = Scale(top, from_=10, to=40, <<<<
orient=HORIZONTAL, command=resize)
scale.set(12)
scale.pack(fill=X, expand=1)

quit = Button(top, text='QUIT',
command=top.quit, activeforeground='white',
activebackground='red')
quit.pack()

mainloop()

label and scale are instances.

Colin W.

 

[Bruno Desthuilliers]

Colin J. Williams a écrit snip code binding label and scale)

label and scale are instances.

And ? *Everything* you can bind to a name is an instance.