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How can I assign an individual value to each button in the loop? [duplicate]

This question already has answers here:
tkinter creating buttons in for loop passing command arguments
(3 answers)
Closed 3 years ago.
I am using a for loop and I would like to pass an individual argument to each separate button (in tkinter), this is for a calculator. However, I am unable to find a solution, to make my problem clear I will show the relevant code:
import tkinter as tk
entry_box = tk.Entry(master,width=35)
def insert_value(value):
entry_box.insert(0,value)
buttons = []
for i in range(0,10):
a = tk.Button(master,text=str(i),command=lambda:insert_value(str(i)))
buttons.append(a)
Note: I have removed the .grid() statements in the loop as it removes quite a large and unnecessary portion of code. And also I want each button to insert its displayed value so button 1 would insert 1, 2: 2 etc.
The problem occurs when passing "i" to insert value, as the value inserted into the entry box is always 9. I think this is because "i" will always end on 9 in the loop.
However, I can not find a solution to this. I have tried getting values from lists. I can't think of any other way to do this( in a loop that is).
I know I could just write the statements out 10 times but I am interested to know whether their is a solution.
TL;DR
The value passed to insert value is always 9.
Is there a way to insert the value that each button displays (1 to 9) into the entry box using a for loop?
Regardless of whether it's right all suggestions would be interesting and nice to see. Thankyou.

Since i is a free variable, it isn't evaluated until the callback is actually called, not when the function is first defined.
One hack is to pass the loop index as the default value of an otherwise unused function parameter. Note that you never need the integer i, only the string str(i), so we make the replacement before we call tk.Button.
buttons = []
for i in range(0,10):
i = str(i)
a = tk.Button(master,text=i, command=lambda i=i:insert_value(i))
buttons.append(a)
Another solution is to explicitly define a factory function to create the callback. make_callback is almost identical to the function created by your lambda expression, except it returns a closure around its argument rather than using default parameter values.
def make_callback(i):
return lambda: insert_value(i)
buttons = []
for i in range(0,10):
i = str(i)
a = tk.Button(master,text=i, command=make_callback(i))
buttons.append(a)
In fact, if you wanted, you could "inline" make_callback using nested lambda expressions, though I wouldn't recommend it for readability.
buttons = []
for i in range(0,10):
i = str(i)
a = tk.Button(master,text=i, command=(lambda x: lambda: insert_value(x))(i))
buttons.append(a)

below an oo solution.
#!/usr/bin/python3
import tkinter as tk
from tkinter import ttk
from tkinter import messagebox
class App(tk.Tk):
def __init__(self):
super().__init__()
self.protocol("WM_DELETE_WINDOW", self.on_exit)
self.count = tk.IntVar()
self.set_title()
self.set_style()
self.init_ui()
def init_ui(self):
self.f = ttk.Frame()
self.label = ttk.Label(self.f, text="Hello, world!")
self.entry_box = ttk.Entry(self.f,textvariable=self.count)
self.entry_box.bind('<Return>', self.on_load_buttons)
self.label.grid(row=0,column=1, sticky=tk.W)
self.entry_box.grid(row=1, column=1, sticky=tk.W)
self.f.grid(row=0, column=0, sticky=tk.N+tk.W+tk.S+tk.E)
def on_load_buttons(self, evt=None):
if self.count.get():
for i in range(0,self.count.get()):
ttk.Button(self.f, text=str(i),
command=lambda:insert_value(str(i))).grid(row=i,
column=3,
sticky=tk.W+tk.E,
padx=5, pady=5)
def set_style(self):
self.style = ttk.Style()
self.style.theme_use("clam")
def set_title(self):
s = "{0}".format('Hello World')
self.title(s)
def on_exit(self):
"""Close all"""
if messagebox.askokcancel(self.title(), "Do you want to quit?", parent=self):
self.destroy()
if __name__ == '__main__':
app = App()
app.mainloop()

tkinter button in class can't call function

Total noob, seriously and angrily struggling with Python...
What I'm trying to do SHOULD be simple:
Make a button.
Connect that button go a function.
Click button --> run function.
The problem comes when we have to use CLASS (which, no matter how much I read, study - or even pay to take classes continues to make zero sense to me)...
I've tried every concieveable combination of putting this little convert() function IN the class, of adding self.convert or root.convert - and NONE of it works. And, I am clueless why - or what to try next.
Here's the code:
from tkinter import *
from tkinter.ttk import Frame, Button, Style
def convert():
print("clicked")
kg = entry_kg.get()
print(kg)
class Example(Frame):
def __init__(self):
super().__init__()
self.initUI() # initiate the GUI
# -------------------------------
def initUI(self):
self.master.title("Weight Converter")
self.pack(fill=BOTH, expand=True)
# -------------------------------------
frame_kg = Frame(self) # frame for Kilograms
frame_kg.pack(fill=X)
lbl_kg = Label(frame_kg, text="Kilograms", width=16)
lbl_kg.pack(side=LEFT, padx=5, pady=5)
entry_kg = Entry(frame_kg)
entry_kg.pack(fill=X, padx=(5, 30), expand=True)
# ------------------------------------------------
frame_btn = Frame(self) # frame for buttons
frame_btn.pack(fill=BOTH, expand=True, padx=20, pady=5)
btn_convert=Button(frame_btn, text="Convert", command=convert)
btn_convert.pack(side=LEFT, padx=5, pady=5)
# -------------------------------------------
def main():
root = Tk()
root.geometry("300x200+300+200")
app = Example()
root.mainloop()
if __name__ == '__main__':
main()
What am I doing wrong?
How to do it right?
The seemingly arbitrary and useless over-complication of a simple task is seriously maddening...

If you want your functions to be designed outside of the class, but want to call it from a button defined in the class, the solution is to create a method in your class which takes the input values and then passes them to the external function.
This is called decoupling. Your function is decoupled from the implementation of the UI, and it means that you are free to completely change the implementation of the UI without changing the function, and vice versa. It also means that you can reuse the same function in many different programs without modification.
The overall structure of your code should look something like this:
# this is the external function, which could be in the same
# file or imported from some other module
def convert(kg):
pounds = kg * 2.2046
return pounds
class Example(...):
def initUI(self):
...
self.entry_kg = Entry(...)
btn_convert=Button(..., command=self.do_convert)
...
def do_convert(self):
kg = float(self.entry_kg.get())
result = convert(kg)
print("%d kg = %d lb" % (kg, result))

Here's a modified version of your code that works. The changes have been indicated with ALL CAPS line comments. I obviously misunderstood your question (which does say you could figure out how to make the convert() function part of the class. However, you mentioned you wanted the opposite of that, so I'm modified the code here accordingly.
Essentially the problem boils down to the convert() function needing to access a tkinter.Entry widget that's created somewhere else—inside your Example class in this case.
One way of doing that would be to save the widget in a global variable and access it through the variable name assigned to it. Many folks do that because it's easiest to thing to do, but as you should know, global variables are considered a bad practice and are generally something to be avoided.
There's a common way to avoid needing one with tkinter, which is sometimes called "The extra arguments trick". To use it all you need to do is create a short anonymous function with an argument that has a default value defined—which in this case will be the Entry widget you want passed to the now "wrapped" convert() function. This can be done using what's called a lambda expression. The revised code below and the comments in it show and describe how to do this:
from tkinter import *
from tkinter.ttk import Frame, Button, Style
def convert(entry_widget): # ADDED WIDGET ARGUMENT
""" Some function outside class. """
print("clicked")
kg = entry_widget.get() # REFERENCE ENTRY WIDGET PASSED AS ARGUMENT
print(kg)
class Example(Frame):
def __init__(self):
super().__init__()
self.initUI() # initiate the GUI
def initUI(self):
self.master.title("Weight Converter")
self.pack(fill=BOTH, expand=True)
frame_kg = Frame(self) # frame for Kilograms
frame_kg.pack(fill=X)
lbl_kg = Label(frame_kg, text="Kilograms", width=16)
lbl_kg.pack(side=LEFT, padx=5, pady=5)
entry_kg = Entry(frame_kg)
entry_kg.pack(fill=X, padx=(5, 30), expand=True)
frame_btn = Frame(self) # frame for buttons
frame_btn.pack(fill=BOTH, expand=True, padx=20, pady=5)
btn_convert=Button(frame_btn, text="Convert",
# DEFINE ANONYMOUS FUNCTION WITH DEFAULT ARGUMENT SO IT'S
# AUTOMATICALLY PASSED TO THE TARGET FUNCTION.
command=lambda entry_obj=entry_kg: convert(entry_obj))
btn_convert.pack(side=LEFT, padx=5, pady=5)
def main():
root = Tk()
root.geometry("300x200+300+200")
app = Example()
root.mainloop()
if __name__ == '__main__':
main()

Your entry_kg is not known anywhere outside the scope of initUI method. That is why. You could convert it from a method variable to instance attribute to be within reach for class methods by replacing:
entry_kg = Entry(frame_kg)
entry_kg.pack(fill=X, padx=(5, 30), expand=True)
with:
self.entry_kg = Entry(frame_kg)
self.entry_kg.pack(fill=X, padx=(5, 30), expand=True)
Only then:
You can mention it in a class method like:
...
kg = self.entry_kg.get()
That way you if you make your convert a method under Example again:
def initUI(self):
...
def convert(self): # is defined under the same scope as initUI
print("clicked")
kg = self.entry_kg.get() # notice that it now refers to self.e...
print(kg)
also don't forget to replace command option as well:
btn_convert=Button(..., command=self.convert)
Or only then:
When outside the class scope, by using dot notation on the object that the class creates:
def main():
root = Tk()
root.geometry("300x200+300+200")
app = Example()
kg = app.entry_kg.get() # This would return an empty string, but it would still be valid
root.mainloop()
to be used with global methods, such as the current state of convert you need to make app (the object it is an attribute of) global, or pass it explicitly to the method.

Tkinter Text Window, update on open and close

I am trying to create a Tkinter app, where when you press a button, a new Window opens which has continually updating text about certain parts of the program. My problem is the section of code where I am trying to add the text to the screen. This is what I have written:
import tkinter as tk
import time
class TextWindow(tk.Frame):
def __init__(self, parent):
tk.Frame.__init__(self, parent)
self.textArea = tk.Text(self, height = 10, width = 30)
self.textArea.pack(side = "left", fill = "y")
bar = tk.Scrollbar(self)
bar.pack(side = "right", fill = "y")
bar.config(command = self.textArea.yview)
def output(self, value):
outputVal = str(value)
self.textArea.inser('end', "{0}\n".format(outputVal))
self.textArea.see('end')
def openWindow():
textWindow = tk.Toplevel(root)
textFrame = TextWindow(textWindow)
textFrame.pack()
value = 0.0
alive = True
while alive:
if textWindow.winfo_exists:
value = value + 0.1
textFrame.output(value)
time.sleep(0.1)
else:
alive = False
root = tk.Tk
btn = tk.Button(root, text = "Click", command = openWindow)
btn.pack()
root.mainloop()
When I comment out the while loop in the openWindow method, the window opens and closes, and reopens, no problem. However when the code is there, I never see the window when I press the button.
I tried running it through the IDLE debugger, and I am not getting any errors, and everything runs through the loop fine, however the Window still never appears. What is my problem?

The answer that Jason S gave is not a good example. You can avoid any issues with sleep by just using after() instead. Don't settle for "Kinda works".
Here is a break down of how you could accomplish what you need without having the problems associated with sleep() and tkinter.
First you are importing Tk() wrong. Don't do tk.Tk do tk.Tk()
Now lets move the entire program into a single class. This will provide us with the ability to use class attributes and make things a bit easier to work with.
Here we create a class called guiapp(tk.Frame): you can name it what you want but this is just my example. Then make sure you are passing root using guiapp(root) so we can work in this class on the tk.Tk() instance. This will be shown at the bottom of the program where the class is instantiated.
Because we have passed root to the class we can place the button that opens the Toplevel window on our self.master attribute.
UPDATE: Changed how data is sent to the Textbox in Toplevel so we can retain the information in case you want to reopen top level. per your comment.
import tkinter as tk
class guiapp(tk.Frame):
def __init__(self, master):
tk.Frame.__init__(self, master)
self.master = master
self.value = 0.0
self.alive = True
self.list_for_toplevel = [] # added list to retain values for Toplevel
btn = tk.Button(self.master, text = "Click", command = self.TextWindow)
btn.pack()
Here we add the method to define the Topelevel we are going to create.
Because everything is inside this one class we can create this Topelevel as a Toplevel of self.master. At the end of this method we call the self.timed_loop() method I added that manages the timed portion of your program. UPDATE: added a call to a new function.
def TextWindow(self):
self.textWindow = tk.Toplevel(self.master)
self.textFrame = tk.Frame(self.textWindow)
self.textFrame.pack()
self.textArea = tk.Text(self.textWindow, height = 10, width = 30)
self.textArea.pack(side = "left", fill = "y")
bar = tk.Scrollbar(self.textWindow)
bar.pack(side = "right", fill = "y")
bar.config(command = self.textArea.yview)
self.alive = True
self.add_list_first()
UPDATE: Added a new function called add_list_first(self):. This will allow us to first add any values that are stored in the list then we can call timed_loop() to continue appending the list and counting.
def add_list_first(self):
for item in self.list_for_toplevel:
self.textArea.insert('end', "{}\n".format(item))
self.textArea.see('end')
self.timed_loop()
Here we have created a method to perform the task you have in you code for the Toplevel that uses the after() function from tkinter. ever 1000 is equal to 1 second, so play with that timer if you want. The first part of after() is for the time in milliseconds and the 2nd part is the function being called. In this case it calls itself to continue the loop until either the Toplevel window self.textWindow is closed or the self.alive variable is no longer True.
UPDATE: I have added a for loop to insert the list instead of directly imputing each value. This way we can retain the data if we want to reopen the Toplevel.
def timed_loop(self):
if self.alive == True and tk.Toplevel.winfo_exists(self.textWindow):
self.master.after(1000, self.timed_loop)
self.value += 1
self.list_for_toplevel.append(self.value)
self.textArea.delete(1.0, "end-1c")
for item in self.list_for_toplevel:
self.textArea.insert('end', "{}\n".format(item))
self.textArea.see('end')
else:
self.alive = False
This is the preferred way to start your class going in tkinter. As you can see we have created root as tk.Tk() and passed root into the the class guiapp(). Also note that I assigned this instance of the class to the variable name myapp. This will allow us to interact with the class from outside of the class if you ever need to. It does not make a difference in this case but I thought I would add it just the same.
if __name__ == "__main__":
root = tk.Tk()
myapp = guiapp(root)
root.mainloop()
Here is the copy paste version for you to use.
import tkinter as tk
class guiapp(tk.Frame):
def __init__(self, master):
tk.Frame.__init__(self, master)
self.master = master
self.value = 0.0
self.alive = True
self.list_for_toplevel = []
btn = tk.Button(self.master, text = "Click", command = self.TextWindow)
btn.pack()
def TextWindow(self):
self.textWindow = tk.Toplevel(self.master)
self.textFrame = tk.Frame(self.textWindow)
self.textFrame.pack()
self.textArea = tk.Text(self.textWindow, height = 10, width = 30)
self.textArea.pack(side = "left", fill = "y")
bar = tk.Scrollbar(self.textWindow)
bar.pack(side = "right", fill = "y")
bar.config(command = self.textArea.yview)
self.alive = True
self.add_list_first()
def add_list_first(self):
for item in self.list_for_toplevel:
self.textArea.insert('end', "{}\n".format(item))
self.textArea.see('end')
self.timed_loop()
def timed_loop(self):
if self.alive == True and tk.Toplevel.winfo_exists(self.textWindow):
self.master.after(1000, self.timed_loop)
self.value += 1
self.list_for_toplevel.append(self.value)
outputVal = str(self.value)
self.textArea.insert('end', "{0}\n".format(outputVal))
self.textArea.see('end')
else:
self.alive = False
if __name__ == "__main__":
root = tk.Tk()
myapp = guiapp(root)
root.mainloop()

The problem is that you are never giving control back to the Tkinter main loop. The code gets stuck executing in the while loop, meaning Tkinter never gets to refresh the display or process any other events. You could force update by calling root.update() right before time.sleep(0.1), but this is not really optimal and the display will be unresponsive while sleeping. Depending on what you are doing, it may be good enough.
See here for additional explanation

How to call a function whenever global variable changes it value?

How can I call a function change_label whenever global variable a changes its value? With change_variable I am trying to simulate actual changing of the variable (the variable changes on button click).
from tkinter import *
a = 3
class Application(Frame):
def __init__(self, master):
Frame.__init__(self, master)
self.master = master
self.button = Button(self.master, text='Change Variable', command=self.change_variable)
self.button.grid(row=0)
self.label = Label(self.master, text='Test')
self.label.grid(row=1)
def change_label(self):
self.label.config(bg='Red', fg='Yellow')
def change_variable(self):
global a
a = 1
def main():
root = Tk()
Application(root)
root.mainloop()
if __name__ == '__main__':
main()

If you use one of tkinters special variables (StringVar, etc) you can add a "trace" that will trigger a callback whenever the variable is set or unset.
For example:
class Application(Frame):
def __init__(self, master):
Frame.__init__(self, master)
...
self.a = tk.IntVar(value=3)
self.a.trace("w", self.change_label)
...
def change_label(self, *args):
self.label.config(bg='Red', fg='Yellow')
def change_variable(self):
self.a.set(1)
With that, whenever you set the value of self.a via the set method, the function bound with the trace will be called.
Any widget that uses that variable also will be updated. For example, change your label to this:
self.label = tk.Label(self.master, textvariable=self.a)
When you click the button, notice that the label changes to reflect the change.
For a description of what arguments are passed to the trace function, see What are the arguments to Tkinter variable trace method callbacks?
These variables have a good description here: The Variable Classes (BooleanVar, DoubleVar, IntVar, StringVar)

If you are using Tk, this might be worth looking into: Tk's "Variable" classes
If that doesn't work for you (because you want to store your own type, or something like that), Shiva's comment is the way to go, and if you want to store multiple variables, this might be a good idea:
class Storage(dict):
def __getattribute__(self, name):
return self[name]
def __setattr__(self, name, value):
print(name, value) # react to the change of name
self[name] = value
storage = Storage({a: 3, b: 2})
storage.a = 4
print(storage.a)
If you don't want to be able to set the variable without triggering some code you put there, good luck. You can override __setitem__ too, but you can always call dict.__setitem__ with the Storage variable as the first argument.

Try running this code it will give you the idea of what you want.
import tkinter
count = 5
def change_text():
global count
if count != 2:
button.config(text='edit')
frame = tkinter.Frame(height=500,width=500)
button = tkinter.Button(frame,text='save',command=change_text)
button.place(x=0,y=0)
frame.pack()
frame.mainloop()

The code was supposed be like this.
from tkinter import *
a = 3
class Application(Frame):
def __init__(self, master):
Frame.__init__(self, master)
self.master = master
self.button = Button(self.master, text='Change Variable', command=self.change_label)
self.button.grid(row=0)
self.label = Label(self.master, text='Test')
self.label.grid(row=1)
def change_label(self):
global a
a = 1
if a != 3:
self.label.config(bg='Red', fg='Yellow')
def main():
root = Tk()
Application(root)
root.mainloop()
hope that is what you wanted.

tkinter variable in another class

Python 3.1, tkinter/ttk
I wrote something very simple to try and understand how tkinter's variables linked to widgets can be stored in a different class to the widget. Code below.
Questions:
1) why doesn't pressing the button change the label?
2) do I need quite so many selfs? Can the variables within each method manage without self. on the start?
Hopefully the answer will be a useful learning exercise for other tkinter newbies...
from tkinter import *
from tkinter.ttk import *
root = Tk()
class Store:
def __init__(self):
self.v = IntVar()
self.v.set(0)
def set(self, v):
self.v.set(v)
class Main:
def __init__(self):
self.counter = 0
self.label = Label(root, textvariable = a.v)
self.label.pack()
self.button = Button(root, command = self.counter, text = '+1')
self.button.pack()
def counter(self):
self.counter = self.counter + 1
a.set(self.counter)
a = Store()
b = Main()
root.mainloop()

Your problem is that you have both a method and a variable named counter. When you click the button, your function isn't being called so the variable isn't being set. At the time you create the button, tkinter thinks that self.counter is a variable rather than a command.
The solution to this particular problem is to rename either the function or the variable. It then should work as you expect.
To answer the question about "too many selfs": you need to use self so that python knows that the object you are referring to should be available everywhere within a specific instance of the object. So, yes, you need all those self's, if you want to refer to variables outside of the function they are defined in.
As for self in the definition of a method, those too are necessary. When you do object.method(), python will automatically send a reference to the object as the first argument to a method, so that the method knows specifically which method is being acted upon.
If you want to know more about the use of "self", there's a specific question related to self here: What is the purpose of self?

If I were you, I will do this:
import tkinter
root = tkinter.Tk()
var = tkinter.IntVar()
label = tkinter.Label(root, textvariable=var)
button = tkinter.Button(root, command=lambda: var.set(var.get() + 1), text='+1')
label.pack()
button.pack()
root.mainloop()
UPDATE:
But, if you insist doing this with two classes (where the first class is only a somewhat pointless interface), then I would do this:
import tkinter
class Store:
def __init__(self):
self.variable = tkinter.IntVar()
def add(self, value):
var = self.variable
var.set(var.get() + value)
return var.get()
class Main(tkinter.Tk):
def __init__(self, *args, **kwargs):
tkinter.Tk.__init__(self, *args, **kwargs)
var = Store()
self.label = tkinter.Label(self, textvariable=var.variable)
self.button = tkinter.Button(self, command=lambda: var.add(1), text='+1')
self.label.pack()
self.button.pack()
root = Main()
root.mainloop()
As you may notice, I used in both times the get() and set() methods of the IntVar (in your version I do this thru the Store interface we made), therefore you don't need to use a new variable (like self.counter) because the variable we instantiated is storing the data.
The other thing I used is a lambda expression instead of a full-blown function definition, since we only want to get the current value, add 1 to it, and store it as the new value.
And in my version, the Main class is a subclass of the original tkinter.Tk class -- that's why I call it's __init__ method inside the Main's __init__ method.