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manipulate dynamically generated tk-inter widgets without global variables

This code of a minimal example is functional:
from tkinter import *
textbox =str()
def openpopup():
popupwindow = Toplevel(root)
global textbox
textbox = Text(popupwindow, height=20, width=40,font="Courier")
textbox.pack()
textbox.delete(1.0, END)
textbox.insert(1.0,"start")
Button(popupwindow, text="do it", command=changepopup).pack()
def changepopup():
global textbox
textbox.delete(1.0, END)
textbox.insert(1.0,"changed text")
root = Tk()
Button(root, text="open", command=openpopup).pack()
mainloop()
my goal is to open a popup dynamically on userinput and then have various gui elements interact.
I managed to do this using global. I've read using global variables should be avoided.
What is the recommended way of going about this? Can I avoid using globals? I am aware that this is an issue of scoping, this is how I came up with this "solution". I am not so familiar with OOP but I have a hunch this might be a solution here.

Question: Can I avoid using globals?
Yes, consider this OOP solution without any global.
Reference:
- 9.5. Inheritance
- class-and-instance-variables
- Dialog Windows
import tkinter as tk
from tkinter import tkSimpleDialog
class Popup(tkSimpleDialog.Dialog):
# def buttonbox(self):
# override if you don't want the standard buttons
def body(self, master):
self.text_content = ''
self.text = tk.Text(self)
self.text.pack()
return self.text # initial focus
def apply(self):
self.text_content = self.text.get(1.0, tk.END)
class App(tk.Tk):
def __init__(self):
super().__init__()
btn = tk.Button(self, text='Popup', command=self.on_popup)
btn.pack()
def on_popup(self):
# The widget `Popup(Dialog)`, waits to be destroyed.
popup = Popup(self, title='MyPopup')
print(popup.text_content)
if __name__ == '__main__':
App().mainloop()

The object-oriented way would be to create a class representing "popup" objects. The class' initializer method, __init__(), can create the popup's widgets as well as act as a storage area for the contents of the Text widget. This avoids needing a global variable because methods of class all has an first argument usually call self the is instance of the class.
Any data needed can be stored as attributes of self and can easily be "shared" all the methods of the class.
The other primary way to avoid global variables is by explicitly passing them as arguments to other callables — like main() does in the sample code below.
Here's an example based on the code in your question:
from tkinter import *
class Popup:
def __init__(self, parent):
popup_window = Toplevel(parent)
self.textbox = Text(popup_window, height=20, width=40, font="Courier")
self.textbox.pack()
self.textbox.insert(1.0, "start")
btn_frame = Frame(popup_window)
Button(btn_frame, text="Do it", command=self.do_it).pack(side=LEFT)
Button(btn_frame, text="Close", command=popup_window.destroy).pack(side=LEFT)
btn_frame.pack()
def do_it(self):
self.clear()
self.textbox.insert(1.0, "changed text")
def clear(self):
self.textbox.delete(1.0, END)
def main():
root = Tk()
Button(root, text="Open", command=lambda: Popup(root)).pack()
root.mainloop()
if __name__ == '__main__':
main()

The global you created, textbox is unnecessary. You can simply remove it from your program. and still get the same behavior
# textbox = str()
I hope my answer was helpful.

how can i use the Entry function in tkinter in an if argument?

So i am making a password organisator in python, and i don't know how i can get user input from an Entry and use it in an if argument?
text1 = StringVar()
def but():
text1.get()
print(text1.get())
knapp2 = Button(root, command="but").pack()
entry1 = Entry(root, textvariable=text1).place(x=270, y=100)

You can call the .get() function on on the Entry widget too to get the text.
import tkinter
from tkinter import Tk, Button, Entry
mw = Tk()
entry = Entry(mw)
entry.pack()
def but():
text = entry.get()
print(text)
button.config(text='Button Clicked')
button = Button(mw, command=but, text='Test')
button.pack()
mw.mainloop()
This code does work but will become complicated with larger code. You will have to define the function before creating a widget that calls that function. In the above example if you created the button widget before the function you would get an exception. You could create the widget, then create the function, then change the configuration of the button to call that function when clicked but that's still pretty complicated and will be confusing in large programs.
I would recommend putting everything in a class. It makes it easy to reference widgets in functions.
import tkinter
from tkinter import Tk, Button, Entry
class Main:
def __init__(self, master):
self.master = master
self.entry = Entry(self.master)
self.entry.pack()
self.button = Button(self.master, text='Test', command=self.But)
self.button.pack()
def But(self):
print(self.entry.get())
self.button.config(text='Button Clicked.')
mw = Tk()
main = Main(mw)
mw.mainloop()

Creating dynamically named gui objects in Python with tkinter

I'm learning to use tkinter in Python 3.6.4. I am creating a GUI with multiple instances of buttons. Two such instances are:
def createWidgets(self):
# first button
self.QUIT = Button(self)
self.QUIT["text"] = "Quit"
self.QUIT["command"] = self.quit
self.QUIT.pack()
# second button
self.Reset = Button(self)
self.Reset["text"] = "Reset"
self.Reset["command"] = "some other function, tbd"
What I want to learn is how to abstract the instantiation of buttons such that each instance in the createWidgets method is based on a method something like this:
createButton( self, text, command, fg, bg, hgt, wth, cursor ):
What I don't know is how to control the naming of the button as:
self.QUIT
self.Reset
where the property or name following the "." operator can be passed to the createButton as a property by which the button is created and named.

Simply expanding on what Brian said, this code will get you going. The button objects are stored in a widget dictionary. Here is one way to put this together:
import tkinter as tk
import sys
root = tk.Tk()
class CustomButton(tk.Button):
def __init__(self, parent, **kwargs):
tk.Button.__init__(self, parent)
for attribute,value in kwargs.items():
try:
self[attribute] = value
except:
raise
def doReset():
print("doRest not yet implemented")
if __name__ == '__main__':
widget = {}
widget['quit'] = CustomButton(root, text='Quit', command=sys.exit)
widget['reset'] = CustomButton(root, text='Reset', command=doReset)
for button in widget.keys():
widget[button].pack()
root.mainloop()

How to delete Tkinter widgets from a window?

I have a list of tkinter widgets that I want to change dynamically.
How to delete the widgets from the window?

You can call pack_forget to remove a widget (if you use pack to add it to the window).
Example:
from tkinter import *
root = Tk()
b = Button(root, text="Delete me", command=lambda: b.pack_forget())
b.pack()
root.mainloop()
If you use pack_forget, you can later show the widget again calling pack again. If you want to permanently delete it, call destroy on the widget (then you won't be able to re-add it).
If you use the grid method, you can use grid_forget or grid_remove to hide the widget.

One way you can do it, is to get the slaves list from the frame that needs to be cleared and destroy or "hide" them according to your needs. To get a clear frame you can do it like this:
from tkinter import *
root = Tk()
def clear():
list = root.grid_slaves()
for l in list:
l.destroy()
Label(root,text='Hello World!').grid(row=0)
Button(root,text='Clear',command=clear).grid(row=1)
root.mainloop()
You should call grid_slaves(), pack_slaves() or slaves() depending on the method you used to add the widget to the frame.

You simply use the destroy() method to delete the specified widgets like this:
lbl = tk.Label(....)
btn = tk.Button(....., command=lambda: lbl.destroy())
Using this you can completely destroy the specific widgets.

You say that you have a list of widgets to change dynamically. Do you want to reuse and reconfigure existing widgets, or create all new widgets and delete the old ones? It affects the answer.
If you want to reuse the existing widgets, just reconfigure them. Or, if you just want to hide some of them temporarily, use the corresponding "forget" method to hide them. If you mapped them with pack() calls, you would hide with pack_forget() (or just forget()) calls. Accordingly, grid_forget() to hide gridded widgets, and place_forget() for placed widgets.
If you do not intend to reuse the widgets, you can destroy them with a straight destroy() call, like widget.destroy(), to free up resources.

clear_btm=Button(master,text="Clear") #this button will delete the widgets
clear_btm["command"] = lambda one = button1, two = text1, three = entry1: clear(one,two,three) #pass the widgets
clear_btm.pack()
def clear(*widgets):
for widget in widgets:
widget.destroy() #finally we are deleting the widgets.

Today I learn some simple and good click event handling using tkinter gui library in python3, which I would like to share inside this thread.
from tkinter import *
cnt = 0
def MsgClick(event):
children = root.winfo_children()
for child in children:
# print("type of widget is : " + str(type(child)))
if str(type(child)) == "<class 'tkinter.Message'>":
# print("Here Message widget will destroy")
child.destroy()
return
def MsgMotion(event):
print("Mouse position: (%s %s)" % (event.x, event.y))
return
def ButtonClick(event):
global cnt, msg
cnt += 1
msg = Message(root, text="you just clicked the button..." + str(cnt) + "...time...")
msg.config(bg='lightgreen', font=('times', 24, 'italic'))
msg.bind("<Button-1>", MsgClick)
msg.bind("<Motion>", MsgMotion)
msg.pack()
#print(type(msg)) tkinter.Message
def ButtonDoubleClick(event):
import sys; sys.exit()
root = Tk()
root.title("My First GUI App in Python")
root.minsize(width=300, height=300)
root.maxsize(width=400, height=350)
button = Button(
root, text="Click Me!", width=40, height=3
)
button.pack()
button.bind("<Button-1>", ButtonClick)
button.bind("<Double-1>", ButtonDoubleClick)
root.mainloop()
Hope it will help someone...

You can use forget method on the widget
from tkinter import *
root = Tk()
b = Button(root, text="Delete me", command=b.forget)
b.pack()
b['command'] = b.forget
root.mainloop()

I found that when the widget is part of a function and the grid_remove is part of another function it does not remove the label. In this example...
def somefunction(self):
Label(self, text=" ").grid(row = 0, column = 0)
self.text_ent = Entry(self)
self.text_ent.grid(row = 1, column = 0)
def someotherfunction(self):
somefunction.text_ent.grid_remove()
...there is no valid way of removing the Label.
The only solution I could find is to give the label a name and make it global:
def somefunction(self):
global label
label = Label(self, text=" ")
label.grid(row = 0, column = 0)
self.text_ent = Entry(self)
self.text_ent.grid(row = 1, column = 0)
def someotherfunction(self):
global label
somefunction.text_ent.grid_remove()
label.grid_remove()
When I ran into this problem there was a class involved, one function being in the class and one not, so I'm not sure the global label lines are really needed in the above.

How to run a code whenever a Tkinter widget value changes?

I'm using Python and Tkinter, and I want the equivalent of onchange event from other toolkits/languages. I want to run code whenever the user updates the state of some widgets.
In my case, I have many Entry, Checkbutton, Spinbox and Radiobutton widgets. Whenever any one of these changes, I want to run my code (in this case, update a text box on the other panel).
(just remember that user may interact with those widgets using either mouse or keyboard, and even using Ctrl+V to paste text)

I think the correct method is to use trace on a tkinter variable that has been assigned to a widget.
For example...
import tkinter
root = tkinter.Tk()
myvar = tkinter.StringVar()
myvar.set('')
mywidget = tkinter.Entry(root,textvariable=myvar,width=10)
mywidget.pack()
def oddblue(a,b,c):
if len(myvar.get())%2 == 0:
mywidget.config(bg='red')
else:
mywidget.config(bg='blue')
mywidget.update_idletasks()
myvar.trace('w',oddblue)
root.mainloop()
The w in trace tells tkinter whenever somebody writes (updates) the variable, which would happen every time someone wrote something in the Entry widget, do oddblue. The trace always passes three values to whatever function you've listed, so you'll need to expect them in your function, hence a,b,c. I usually do nothing with them as everything I need is defined locally anyway. From what I can tell a is the variable object, b is blank (not sure why), and c is the trace mode (i.e.w).
For more info on tkinter variables check this out.

How I would solve this in Tcl would be to make sure that the checkbutton, spinbox and radiobutton widgets are all associated with an array variable. I would then put a trace on the array which would cause a function to be called each time that variable is written. Tcl makes this trivial.
Unfortunately Tkinter doesn't support working with Tcl arrays. Fortunately, it's fairly easy to hack in. If you're adventurous, try the following code.
From the full disclosure department: I threw this together this morning in about half an hour. I haven't actually used this technique in any real code. I couldn't resist the challenge, though, to figure out how to use arrays with Tkinter.
import Tkinter as tk
class MyApp(tk.Tk):
'''Example app that uses Tcl arrays'''
def __init__(self):
tk.Tk.__init__(self)
self.arrayvar = ArrayVar()
self.labelvar = tk.StringVar()
rb1 = tk.Radiobutton(text="one", variable=self.arrayvar("radiobutton"), value=1)
rb2 = tk.Radiobutton(text="two", variable=self.arrayvar("radiobutton"), value=2)
cb = tk.Checkbutton(text="checked?", variable=self.arrayvar("checkbutton"),
onvalue="on", offvalue="off")
entry = tk.Entry(textvariable=self.arrayvar("entry"))
label = tk.Label(textvariable=self.labelvar)
spinbox = tk.Spinbox(from_=1, to=11, textvariable=self.arrayvar("spinbox"))
button = tk.Button(text="click to print contents of array", command=self.OnDump)
for widget in (cb, rb1, rb2, spinbox, entry, button, label):
widget.pack(anchor="w", padx=10)
self.labelvar.set("Click on a widget to see this message change")
self.arrayvar["entry"] = "something witty"
self.arrayvar["radiobutton"] = 2
self.arrayvar["checkbutton"] = "on"
self.arrayvar["spinbox"] = 11
self.arrayvar.trace(mode="w", callback=self.OnTrace)
def OnDump(self):
'''Print the contents of the array'''
print self.arrayvar.get()
def OnTrace(self, varname, elementname, mode):
'''Show the new value in a label'''
self.labelvar.set("%s changed; new value='%s'" % (elementname, self.arrayvar[elementname]))
class ArrayVar(tk.Variable):
'''A variable that works as a Tcl array variable'''
_default = {}
_elementvars = {}
def __del__(self):
self._tk.globalunsetvar(self._name)
for elementvar in self._elementvars:
del elementvar
def __setitem__(self, elementname, value):
if elementname not in self._elementvars:
v = ArrayElementVar(varname=self._name, elementname=elementname, master=self._master)
self._elementvars[elementname] = v
self._elementvars[elementname].set(value)
def __getitem__(self, name):
if name in self._elementvars:
return self._elementvars[name].get()
return None
def __call__(self, elementname):
'''Create a new StringVar as an element in the array'''
if elementname not in self._elementvars:
v = ArrayElementVar(varname=self._name, elementname=elementname, master=self._master)
self._elementvars[elementname] = v
return self._elementvars[elementname]
def set(self, dictvalue):
# this establishes the variable as an array
# as far as the Tcl interpreter is concerned
self._master.eval("array set {%s} {}" % self._name)
for (k, v) in dictvalue.iteritems():
self._tk.call("array","set",self._name, k, v)
def get(self):
'''Return a dictionary that represents the Tcl array'''
value = {}
for (elementname, elementvar) in self._elementvars.iteritems():
value[elementname] = elementvar.get()
return value
class ArrayElementVar(tk.StringVar):
'''A StringVar that represents an element of an array'''
_default = ""
def __init__(self, varname, elementname, master):
self._master = master
self._tk = master.tk
self._name = "%s(%s)" % (varname, elementname)
self.set(self._default)
def __del__(self):
"""Unset the variable in Tcl."""
self._tk.globalunsetvar(self._name)
if __name__ == "__main__":
app=MyApp()
app.wm_geometry("400x200")
app.mainloop()

You have three different ways of doing the same:
1) Use the built-in "command" configuration, like the one you use on buttons
import tkinter as tk
from tkinter import messagebox as tk_messagebox
def spinbox1_callback():
tk_messagebox.showinfo("Spinbox callback", "You changed the spinbox.")
if __name__ == "__main__":
master = tk.Tk()
spinbox1 = tk.Spinbox(master, from_=0, to=10, command=spinbox1_callback)
spinbox1.pack()
tk.mainloop()
2) Use the event bindings to capture specific events:
http://effbot.org/tkinterbook/tkinter-events-and-bindings.htm
import tkinter as tk
from tkinter import messagebox as tk_messagebox
root = tk.Tk()
def callback(event):
tk_messagebox.showinfo("clicked at", event.x, event.y)
frame = tk.Frame(root, width=100, height=100)
frame.bind("<Button-1>", callback)
frame.pack()
root.mainloop()
3) "trace" changes on a tkinter variable classes, so if your widget uses a StringVar, BooleanVar, IntVar, or DoubleVar in the textvariable parameter, you will get a callback once it gets updated. https://effbot.org/tkinterbook/variable.htm
import tkinter as tk
from tkinter import messagebox as tk_messagebox
if __name__ == "__main__":
master = tk.Tk()
widget_contents = tk.StringVar()
widget_contents.set('')
some_entry = tk.Entry(master,textvariable=widget_contents,width=10)
some_entry.pack()
def entry1_callback(*args):
tk_messagebox.showinfo("entry callback", "You changed the entry %s" % str(args))
some_entry.update_idletasks()
widget_contents.trace('w',entry1_callback)
tk.mainloop()

It's quite late, but yet, somebody found something that might be useful.
The whole idea comes from #bryan Oakley's post
If I understand well, the main problem is to detech Entry widget's . To detect it in spinbox, Checkbutton and Radiobutton you can use command options when creating widget.
To catch the <onChange> in Entry widget you can use Bryan`s approach using Tcl, which generates this event. As I said, this is not my solution, I've only changed it slightly for this case.
For example:
import tkinter as tk
from tkinter import ttk
def generateOnChange(obj):
obj.tk.eval('''
proc widget_proxy {widget widget_command args} {
# call the real tk widget command with the real args
set result [uplevel [linsert $args 0 $widget_command]]
# generate the event for certain types of commands
if {([lindex $args 0] in {insert replace delete}) ||
([lrange $args 0 2] == {mark set insert}) ||
([lrange $args 0 1] == {xview moveto}) ||
([lrange $args 0 1] == {xview scroll}) ||
([lrange $args 0 1] == {yview moveto}) ||
([lrange $args 0 1] == {yview scroll})} {
event generate $widget <<Change>> -when tail
}
# return the result from the real widget command
return $result
}
''')
obj.tk.eval('''
rename {widget} _{widget}
interp alias {{}} ::{widget} {{}} widget_proxy {widget} _{widget}
'''.format(widget=str(obj)))
def onEntryChanged(event = None):
print("Entry changed")
def onCheckChanged(event = None):
print("Check button changed")
def onSpinboxChanged(event = None):
print("Spinbox changed")
def onRadioChanged(event = None):
print("Radio changed")
if __name__ == '__main__':
root = tk.Tk()
frame = tk.Frame(root, width=400, height=400)
entry = tk.Entry(frame, width=30)
entry.grid(row=0, column=0)
generateOnChange(entry)
entry.bind('<<Change>>', onEntryChanged)
checkbutton = tk.Checkbutton(frame, command=onCheckChanged)
checkbutton.grid(row=1, column=0)
spinbox = tk.Spinbox(frame, width=100, from_=1.0, to=100.0, command=onSpinboxChanged)
spinbox.grid(row=2, column=0)
phone = tk.StringVar()
home = ttk.Radiobutton(frame, text='Home', variable=phone, value='home', command=onRadioChanged)
home.grid(row=3, column=0, sticky=tk.W)
office = ttk.Radiobutton(frame, text='Office', variable=phone, value='office', command=onRadioChanged)
office.grid(row=3, column=0, sticky=tk.E)
frame.pack()
root.mainloop()
Of course modify it to create different callback for plenty of instances (as you mentioned in the question) is easy now.
I hope somebody will find it useful.

So far, I have not encountered any thing equivalent of onChange in Tkinter.
Widgets can be bound to the various events and I have done that explicitly.
http://effbot.org/tkinterbook/tkinter-events-and-bindings.htm