I create a new Button object but did not specify the command option upon creation. Is there a way in Tkinter to change the command (onclick) function after the object has been created?
Though Eli Courtwright's program will work fine¹, what you really seem to want though is just a way to reconfigure after instantiation any attribute which you could have set when you instantiated². How you do so is by way of the configure() method.
from Tkinter import Tk, Button
def goodbye_world():
print "Goodbye World!\nWait, I changed my mind!"
button.configure(text = "Hello World!", command=hello_world)
def hello_world():
print "Hello World!\nWait, I changed my mind!"
button.configure(text = "Goodbye World!", command=goodbye_world)
root = Tk()
button = Button(root, text="Hello World!", command=hello_world)
button.pack()
root.mainloop()
¹ "fine" if you use only the mouse; if you care about tabbing and using [Space] or [Enter] on buttons, then you will have to implement (duplicating existing code) keypress events too. Setting the command option through .configure is much easier.
² the only attribute that can't change after instantiation is name.
Sure; just use the bind method to specify the callback after the button has been created. I've just written and tested the example below. You can find a nice tutorial on doing this at http://www.pythonware.com/library/tkinter/introduction/events-and-bindings.htm
from Tkinter import Tk, Button
root = Tk()
button = Button(root, text="Click Me!")
button.pack()
def callback(event):
print "Hello World!"
button.bind("<Button-1>", callback)
root.mainloop()
Related
i've just started learning tkinter for python, and i'm trying to get the button to change its text when it's clicked on.
this seems like a very simple question, but i can't find any answers. the code i'm using at the moment doesn't work - when the window opens, it displays 'clicked!' as a label above the button immediately, before i've clicked on the button.
from tkinter import *
root = Tk()
def click():
label = Label(root, text = 'clicked!')
label.pack()
button = Button(root, text='click me', command = click())
button.pack()
root.mainloop()
To change an existing button's text (or some other option), you can call its config() method and pass it keyword arguments with new values in them. Note that when constructing the Button only pass it the name of the callback function — i.e. don't call it).
from tkinter import *
root = Tk()
def click():
button.config(text='clicked!')
button = Button(root, text='click me', command=click)
button.pack()
root.mainloop()
You're passing command = click() to the Button constructor. This way, Python executes click, then passes its return value to Button. To pass the function itself, remove the parentheses - command = click.
Good Morning/Evening,
I want to read a number from a spinbox, and if it is 2, it should print something. But my code does not work out. I've tried it with a slider instead of a spinbox and it worked out. But for me, it is really important to use a spinbox, so I hope somebody have an idea.
Code:
from tkinter import *
def a():
if spin.get()==2:
print("Hello World")
root = Tk()
root.geometry('300x100')
spin =Spinbox(root, from_=0, to=10,command=a)
button = Button(root, text='Enter')
button.pack(side=RIGHT)
spin.pack(side=RIGHT)
root.mainloop()
Adding to #coolCloud's answer I would suggest setting a textvariable for spinBox. So if the user changes it using the entry. It would automatically be updated.
Something like this:
from tkinter import *
def a(*event):
if text.get()=='2':
print("Hello World")
root = Tk()
root.geometry('300x100')
text = StringVar()
text.trace('w', a) # or give command=a in the button if you want it to call the event handler only when the button is pressed
spin =Spinbox(root, from_=0, to=10, textvariable=text)
button = Button(root, text='Enter')
button.pack(side=RIGHT)
spin.pack(side=RIGHT)
root.mainloop()
I'm new to Tkinter, I want to print Entry's contents while I'm typing.
Here's my code I've tried:
from tkinter import *
def get_(e):
print(entry.get())
root = Tk()
entry = Entry(root)
entry.pack()
entry.bind("<KeyPress>", get_)
mainloop()
But it seems not "synchronous"(when I type "123" in, output only is "12" and so on)
The following code works properly, but I don't know why:
from tkinter import *
def get_(e):
print(entry.get())
root = Tk()
entry = Entry(root)
entry.pack()
root.bind("<KeyPress>", get_)
## or this: entry.bind("<KeyRelease>", get_)
## or this: entry.bind_all("<KeyPress>", get_)
mainloop()
is there some weird rule I don't know about? Any and all help would be wonderful, thanks in advance!
Question: entry.bind("<KeyPress>" seems not "synchronous" (when I type "123" in output only is "12" and so on ...), while root.bind("<KeyPress>" works.
The event entry.bind("<KeyPress>", ... get fired before the value in tk.Entry is updated. This explains why the output is allways one char behind.
The event root.bind("<KeyPress>", ... get fired after the value in tk.Entry is updated. This explains why this is working.
Alternatives:
Use the "<KeyRelease>" event
tkinter-variable-trace-method
Reference:
Events and Bindings
trace method to attach “observer” callbacks
Write a GUI application with a button labeled "Good-bye". When the
Button is clicked, the window closes.
This is my code so far, but it is not working. Can anyone help me out with my code?
from Tkinter import *
window = Tk()
def close_window (root):
root.destroy()
frame = Frame(window)
frame.pack()
button = Button (frame, text = "Good-bye.", command = close_window)
button.pack()
window.mainloop()
With minimal editing to your code (Not sure if they've taught classes or not in your course), change:
def close_window(root):
root.destroy()
to
def close_window():
window.destroy()
and it should work.
Explanation:
Your version of close_window is defined to expect a single argument, namely root. Subsequently, any calls to your version of close_window need to have that argument, or Python will give you a run-time error.
When you created a Button, you told the button to run close_window when it is clicked. However, the source code for Button widget is something like:
# class constructor
def __init__(self, some_args, command, more_args):
#...
self.command = command
#...
# this method is called when the user clicks the button
def clicked(self):
#...
self.command() # Button calls your function with no arguments.
#...
As my code states, the Button class will call your function with no arguments. However your function is expecting an argument. Thus you had an error. So, if we take out that argument, so that the function call will execute inside the Button class, we're left with:
def close_window():
root.destroy()
That's not right, though, either, because root is never assigned a value. It would be like typing in print(x) when you haven't defined x, yet.
Looking at your code, I figured you wanted to call destroy on window, so I changed root to window.
You could create a class that extends the Tkinter Button class, that will be specialised to close your window by associating the destroy method to its command attribute:
from tkinter import *
class quitButton(Button):
def __init__(self, parent):
Button.__init__(self, parent)
self['text'] = 'Good Bye'
# Command to close the window (the destory method)
self['command'] = parent.destroy
self.pack(side=BOTTOM)
root = Tk()
quitButton(root)
mainloop()
This is the output:
And the reason why your code did not work before:
def close_window ():
# root.destroy()
window.destroy()
I have a slight feeling you might got the root from some other place, since you did window = tk().
When you call the destroy on the window in the Tkinter means destroying the whole application, as your window (root window) is the main window for the application. IMHO, I think you should change your window to root.
from tkinter import *
def close_window():
root.destroy() # destroying the main window
root = Tk()
frame = Frame(root)
frame.pack()
button = Button(frame)
button['text'] ="Good-bye."
button['command'] = close_window
button.pack()
mainloop()
You can associate directly the function object window.destroy to the command attribute of your button:
button = Button (frame, text="Good-bye.", command=window.destroy)
This way you will not need the function close_window to close the window for you.
from tkinter import *
window = tk()
window.geometry("300x300")
def close_window ():
window.destroy()
button = Button ( text = "Good-bye", command = close_window)
button.pack()
window.mainloop()
You can use lambda to pass a reference to the window object as argument to close_window function:
button = Button (frame, text="Good-bye.", command = lambda: close_window(window))
This works because the command attribute is expecting a callable, or callable like object.
A lambda is a callable, but in this case it is essentially the result of calling a given function with set parameters.
In essence, you're calling the lambda wrapper of the function which has no args, not the function itself.
from tkinter import *
def close_window():
import sys
sys.exit()
root = Tk()
frame = Frame (root)
frame.pack()
button = Button (frame, text="Good-bye", command=close_window)
button.pack()
mainloop()
from Tkinter import *
import webbrowser
root = Tk()
frame = Frame(root)
frame.pack()
url = 'http://www.sampleurl.com'
def OpenUrl(url):
webbrowser.open_new(url)
button = Button(frame, text="CLICK", command=OpenUrl(url))
button.pack()
root.mainloop()
My goal is to open a URL when I click the button in the GUI widget. However, I am not sure how to do this.
Python opens two new windows when I run the script without clicking
anything. Additionally, nothing happens when I click the button.
You should use
button = Button(root, text="CLCK", command=lambda aurl=url:OpenUrl(aurl))
this is the correct way of sending a callback when arguments are required.
From here:
A common beginner’s mistake is to call the callback function when
constructing the widget. That is, instead of giving just the
function’s name (e.g. “callback”), the programmer adds parentheses and
argument values to the function:
If you do this, Python will call the callback function before creating
the widget, and pass the function’s return value to Tkinter. Tkinter
then attempts to convert the return value to a string, and tells Tk to
call a function with that name when the button is activated. This is
probably not what you wanted.
For simple cases like this, you can use a lambda expression as a link
between Tkinter and the callback function:
Alternatively, you don't have to pass the URL as an argument of the command. Obviously your OpenUrl method would be stuck opening that one URL in this case, but it would work.
from Tkinter import *
import webbrowser
url = 'http://www.sampleurl.com'
root = Tk()
frame = Frame(root)
frame.pack()
def OpenUrl():
webbrowser.open_new(url)
button = Button(frame, text="CLICK", command=OpenUrl)
button.pack()
root.mainloop()