I am working on a relatively large project, but have managed to recreate my problem in just a few lines:
import tkinter as tk
root = tk.Tk()
root.geometry('200x200')
def doStuff():
pass
sv = tk.StringVar()
def callback():
print(E.get())
doStuff()
return True
E = tk.Entry(root, bg="white", fg="black", width=24, textvariable=sv, validate="key",validatecommand=callback)
E.grid(row=0, column=0, padx=30, pady=5, sticky=tk.E)
root.mainloop()
The desired output would be that every time the user changes the entry in this Entrywidget, a function is called.
This works just fine, but using E.get() returns the 'previous' entry, for example:
-entry is 'boo'
-E.get() is 'bo'
Python seems to run Callback() before the Entry Widget has been changed.
Validation by design happens before the text has been inserted or deleted. For validation to work, it must be able to prevent the data from being changed.
If you aren't doing validation, but instead just want to call a function when the value changes, the best way to do that is to put a trace on the associated variable.
def callback(*args):
print(E.get())
doStuff()
return True
sv = tk.StringVar()
sv.trace_add("write", callback)
Related
There's an example of my code below.
I am trying to make a GUI with tkinter, in python. I want an app that has a variable, let's say var_list, that is introduced into a function as a parameter.I run this function using a button with command=lambda: analize(var_list)
I want to be able to modify the variable by pressing buttons (buttons to add strings to the list). And I have a function for that aswell:
def button_clicked(e):
if ((e["text"]).lower()) in var_list:
var_list.pop(var_list.index((e["text"]).lower())) #this adds a string to the list
else:
var_list.append((e["text"]).lower()) #this deletes the string from the list if it was already there
The function works, I tried printing the var_list and it gets updated everytime I press a button.
The problem is that I have to create the var_list as an empty list before, and when I run the function analize(var_list), it uses the empty list instead of the updated one.
Any idea on how to update the global var everytime I add/delete something from the list?
from tkinter import *
from PIL import ImageTk
def show_frame(frame):
frame.tkraise()
def button_clicked(e):
if ((e["text"]).lower()) in var_list:
var_list.pop(var_list.index((e["text"]).lower()))
else:
var_list.append((e["text"]).lower())
def analize(x):
#does stuff with the list
window = Tk()
frame1 = Frame(window)
frame2 = Frame(window)
canvas1 = Canvas(frame1,width = 1280, height = 720)
canvas1.pack(expand=YES, fill=BOTH)
image = ImageTk.PhotoImage(file="background.png")
var_list = []
button1 = Button(canvas1, text="Analize",font=("Arial"),justify=CENTER, width=10, command=lambda: [show_frame(frame2),analize(x=var_list)])
button1.place(x=(1280/2)-42, y=400)
button2 = Button(canvas1, text="String1",font=("Arial"),justify=CENTER, width=10, command=lambda: button_clicked(button2))
button2.place(x=(1280/2)-42, y=450)
button3 = Button(canvas1, text="String2",font=("Arial"),justify=CENTER, width=10, command=lambda: button_clicked(button3))
button3.place(x=(1280/2)-42, y=500)
Thank you
you can make a global variable eg:-global var
Now you can access it within other defination to manipulate the variable like this
global var
var = 0 # if you want to set a default value to the variable before calling the
function
def change_var():
global var
var = 1
USE OF GLOBAL
using global is highly recommended and is quite necessary if you are working with functions that contain or has the need to manipulate the variable
If global is not given inside the function, the variable will live inside the function and it cannot be accessed outside the function.
Hope this answer was helpful, btw, I am not sure if this the answer you are looking for as your question is not clear, maybe give a situation where you might think it might be necessary to change or update the variable
Sorry, I did not understand you but I guess this example will help you -
import tkinter as tk
root = tk.Tk()
var_list = []
def change_val(n):
var_list.append(n)
label1.config(text=var_list)
def remove():
try:
var_list.pop()
label1.config(text=var_list)
except:
pass
label1 = tk.Label(root,text=var_list)
label1.pack()
button1 = tk.Button(root,text='1',command=lambda:change_val(1))
button1.pack()
button2 = tk.Button(root,text='2',command=lambda:change_val(2))
button2.pack()
button3 = tk.Button(root,text='3',command=lambda:change_val(3))
button3.pack()
button4 = tk.Button(root,text='Pop Element',command=remove)
button4.pack()
root.mainloop()
The code is below from this post:
Why is Tkinter Entry's get function returning nothing?
The argument in the return_entry is 'en' and when I deleted it out it says a positional argument is missing. What is the def return_entry('en') mean and why does it only work with it.
Why cant i just use:
def return_entry():
The en argument makes no sense to me...
from tkinter import *
master = Tk()
def return_entry(en):
content = entry.get()
print(content)
Label(master, text="Input: ").grid(row=0, sticky=W)
entry = Entry(master)
entry.grid(row=0, column=1)
# Connect the entry with the return button
entry.bind('<Return>', return_entry)
mainloop()
Error:
TypeError: return_entry() takes 0 positional arguments but 1 was given
Only throws an error when I remove en and hit enter after I enter input in the entry box.
bind expects function which can get argument to send event to this function - and it will run it as return_entry(event). And this is why you can't use function without argument.
You can even use this event to get access to entry - so you can assing the same function to different entries and ifunction will get text from correct entry
def return_entry(event):
content = event.widget.get()
print(content)
Sometimes we may want to use the same function with command= which doesn't send event to function and then we can use event=None but then we can't use event inside function
def return_entry(event=None):
content = entry.get()
print(content)
entry.bind('<Return>', return_entry)
tk.Button(..., command=return_entry)
Working examples:
Function binded to two entries:
import tkinter as tk
def return_entry(event):
content = event.widget.get()
print(content)
root = tk.Tk()
entry1 = tk.Entry(root)
entry1.pack()
entry1.bind('<Return>', return_entry)
entry2 = tk.Entry(root)
entry2.pack()
entry2.bind('<Return>', return_entry)
root.mainloop()
Function assigned to Entry and Button
import tkinter as tk
def return_entry(event=None):
content = entry.get()
print(content)
root = tk.Tk()
entry = tk.Entry(root)
entry.pack()
entry.bind('<Return>', return_entry)
button = tk.Button(root, text='OK', command=return_entry)
button.pack()
root.mainloop()
I'm trying to use an Entry field to get manual input, and then work with that data.
All sources I've found claim I should use the get() function, but I haven't found a simple working mini example yet, and I can't get it to work.
I hope someone can tel me what I'm doing wrong. Here's a mini file:
from tkinter import *
master = Tk()
Label(master, text="Input: ").grid(row=0, sticky=W)
entry = Entry(master)
entry.grid(row=0, column=1)
content = entry.get()
print(content) # does not work
mainloop()
This gives me an Entry field I can type in, but I can't do anything with the data once it's typed in.
I suspect my code doesn't work because initially, entry is empty. But then how do I access input data once it has been typed in?
It looks like you may be confused as to when commands are run. In your example, you are calling the get method before the GUI has a chance to be displayed on the screen (which happens after you call mainloop.
Try adding a button that calls the get method. This is much easier if you write your application as a class. For example:
import tkinter as tk
class SampleApp(tk.Tk):
def __init__(self):
tk.Tk.__init__(self)
self.entry = tk.Entry(self)
self.button = tk.Button(self, text="Get", command=self.on_button)
self.button.pack()
self.entry.pack()
def on_button(self):
print(self.entry.get())
app = SampleApp()
app.mainloop()
Run the program, type into the entry widget, then click on the button.
You could also use a StringVar variable, even if it's not strictly necessary:
v = StringVar()
e = Entry(master, textvariable=v)
e.pack()
v.set("a default value")
s = v.get()
For more information, see this page on effbot.org.
A simple example without classes:
from tkinter import *
master = Tk()
# Create this method before you create the entry
def return_entry(en):
"""Gets and prints the content of the entry"""
content = entry.get()
print(content)
Label(master, text="Input: ").grid(row=0, sticky=W)
entry = Entry(master)
entry.grid(row=0, column=1)
# Connect the entry with the return button
entry.bind('<Return>', return_entry)
mainloop()
*
master = Tk()
entryb1 = StringVar
Label(master, text="Input: ").grid(row=0, sticky=W)
Entry(master, textvariable=entryb1).grid(row=1, column=1)
b1 = Button(master, text="continue", command=print_content)
b1.grid(row=2, column=1)
def print_content():
global entryb1
content = entryb1.get()
print(content)
master.mainloop()
What you did wrong was not put it inside a Define function then you hadn't used the .get function with the textvariable you had set.
you need to put a textvariable in it, so you can use set() and get() method :
var=StringVar()
x= Entry (root,textvariable=var)
Most of the answers I found only showed how to do it with tkinter as tk. This was a problem for me as my program was 300 lines long with tons of other labels and buttons, and I would have had to change a lot of it.
Here's a way to do it without importing tkinter as tk or using StringVars. I modified the original mini program by:
making it a class
adding a button and an extra method.
This program opens up a tkinter window with an entry box and an "Enter" button. Clicking the Enter button prints whatever is in the entry box.
from tkinter import *
class mini():
def __init__(self):
master = Tk()
Label(master, text="Input: ").grid(row=0, sticky=W)
Button(master, text='Enter', command=self.get_content).grid(row=1)
self.entry = Entry(master)
self.entry.grid(row=0, column=1)
master.mainloop()
def get_content(self):
content = self.entry.get()
print(content)
m = mini()
from tkinter import *
master = Tk()
e1 = Entry(master)
us = e1.get() # doesn't work
def factorize(us):
product=1
for x in range(1,us+1): # gives error here
product=product*x
print(product)
Label(master, text="Number").grid(row=0)
e1.grid(row=0, column=1)
e1.get()))
Button(master, text='Quit', command=master.quit).grid(row=3, column=0, sticky=W, pady=4)
Button(master, text='ans', command=factorize).grid(row=3, column=1, sticky=W, pady=4)
mainloop()
Few problems that I see:
-The example code you provided was a mess, that could be due to poor formatting but regardless, I've fixed it for my example.
-You are calling e1.get() once, after creating the Entry. This would return an empty string; however you don't actually do anything with the stored variable anyway so it's useless. us is never used.
-The command = factorize doesn't pass a variable, and factorize requires a variable. I've changed this so that the callback will pass in the Entry widget. In this way, we can call us = int(e1.get()) inside the function, so that every time the button is clicked, we get the newest entry value.
To do this, I changed the command to command = lambda: factorize(e1). lambda essentially declares an 'anonymous function'. It is the only way to pass variables from a callback using Tkinter, because the command keyword expects the name of a function, example command = master.destroy. Speaking of, I also changed master.quit to master.destroy because you most likely want to destroy it.
-I've wrapped us = int(e1.get()) in a try/catch block, because you want an int for your function. Entry.get() will return a string which you can't use to create a range.
-Finally I've imported tkMessageBox so that I can produce a nice error message when you give a bad value to the Entry (example, anything that can't be converted to an integer)
from tkinter import *
import tkMessageBox
master= Tk()
e1 = Entry(master)
def factorize(us):
try:
us = int(e1.get())
except ValueError:
tkMessageBox.showerror("Value Error", "Please enter an integer!")
else:
product=1
for x in range(1,us+1):
product=product*x
print(product)
Label(master, text="Number").grid(row=0)
e1.grid(row=0, column=1)
Button(master, text='Quit', command=master.destroy).grid(row=3, column=0, sticky=W, pady=4)
Button(master, text='ans', command=lambda: factorize(e1)).grid(row=3, column=1, sticky=W, pady=4)
master.mainloop( )
The script will insert the the button then it will get the value which is blank
so you need to move the us to into the function and then remove the us from the parameters this will mean that the value is set when the button is clicked
also you should put some try statement to ensure that the program can handle all inputs
I'm trying to use an Entry field to get manual input, and then work with that data.
All sources I've found claim I should use the get() function, but I haven't found a simple working mini example yet, and I can't get it to work.
I hope someone can tel me what I'm doing wrong. Here's a mini file:
from tkinter import *
master = Tk()
Label(master, text="Input: ").grid(row=0, sticky=W)
entry = Entry(master)
entry.grid(row=0, column=1)
content = entry.get()
print(content) # does not work
mainloop()
This gives me an Entry field I can type in, but I can't do anything with the data once it's typed in.
I suspect my code doesn't work because initially, entry is empty. But then how do I access input data once it has been typed in?
It looks like you may be confused as to when commands are run. In your example, you are calling the get method before the GUI has a chance to be displayed on the screen (which happens after you call mainloop.
Try adding a button that calls the get method. This is much easier if you write your application as a class. For example:
import tkinter as tk
class SampleApp(tk.Tk):
def __init__(self):
tk.Tk.__init__(self)
self.entry = tk.Entry(self)
self.button = tk.Button(self, text="Get", command=self.on_button)
self.button.pack()
self.entry.pack()
def on_button(self):
print(self.entry.get())
app = SampleApp()
app.mainloop()
Run the program, type into the entry widget, then click on the button.
You could also use a StringVar variable, even if it's not strictly necessary:
v = StringVar()
e = Entry(master, textvariable=v)
e.pack()
v.set("a default value")
s = v.get()
For more information, see this page on effbot.org.
A simple example without classes:
from tkinter import *
master = Tk()
# Create this method before you create the entry
def return_entry(en):
"""Gets and prints the content of the entry"""
content = entry.get()
print(content)
Label(master, text="Input: ").grid(row=0, sticky=W)
entry = Entry(master)
entry.grid(row=0, column=1)
# Connect the entry with the return button
entry.bind('<Return>', return_entry)
mainloop()
*
master = Tk()
entryb1 = StringVar
Label(master, text="Input: ").grid(row=0, sticky=W)
Entry(master, textvariable=entryb1).grid(row=1, column=1)
b1 = Button(master, text="continue", command=print_content)
b1.grid(row=2, column=1)
def print_content():
global entryb1
content = entryb1.get()
print(content)
master.mainloop()
What you did wrong was not put it inside a Define function then you hadn't used the .get function with the textvariable you had set.
you need to put a textvariable in it, so you can use set() and get() method :
var=StringVar()
x= Entry (root,textvariable=var)
Most of the answers I found only showed how to do it with tkinter as tk. This was a problem for me as my program was 300 lines long with tons of other labels and buttons, and I would have had to change a lot of it.
Here's a way to do it without importing tkinter as tk or using StringVars. I modified the original mini program by:
making it a class
adding a button and an extra method.
This program opens up a tkinter window with an entry box and an "Enter" button. Clicking the Enter button prints whatever is in the entry box.
from tkinter import *
class mini():
def __init__(self):
master = Tk()
Label(master, text="Input: ").grid(row=0, sticky=W)
Button(master, text='Enter', command=self.get_content).grid(row=1)
self.entry = Entry(master)
self.entry.grid(row=0, column=1)
master.mainloop()
def get_content(self):
content = self.entry.get()
print(content)
m = mini()