I'm trying to build a listbox using Tkinter and receive the selected option by clicking it.
import Tkinter as tk
from Tkinter import *
root = tk.Tk()
lst=Listbox(root, height=30, width=50)
lst.insert(1, "hy")
lst.insert(2, "hello")
lst.insert(3, "hey")
lst.pack()
sel = lst.curselection()
print sel
root.mainloop()
However, when I run the code it prints me an empty tuple before I pressed any choise.
Does someone know how to get the selected choise after I press one and not right after I run it?
Thanks a lot :)
You are getting the selection about a millisecond after creating the widget, well before the user has a chance to see the UI much less interact with it.
GUI programs are event based, meaning that things happen in response to events. Events are things like clicking buttons, inserting data into input widgets, and selecting items from listboxes.
You need to do one of two things: create a button or other widget which will get the selected item, or configure it so that a function is called whenever an item is selected.
No matter which solution you use, you will need a function that ultimately calls the curselection method of the listbox to get a list of indices. You can then call the get method to get the selected item or items.
Here's a function definition that will print the selected item, or print "no selection" if nothing is selected. So that it can be resused without modification. we'll define it to take the listbox as an argument.
Note: this example assumes the widget only supports a single select, to keep it simple:
def print_selection(listbox):
selection = listbox.curselection()
if selection:
print(f"selected item: {listbox.get(selection[0])}")
else:
print("nothing is selected")
Using a button
To call this from a button is straight-forward. We just create a button after we create the listbox, and use the command attribute to call the function. Since the function we wrote earlier needs a parameter, we'll use lambda to create a temporary function for the button.
button = tk.Button(root, text="Print Selected Item", command=lambda: print_selection(lst))
button.pack()
Calling the function when the selection is made
To call the function whenever the user changes the selection, we can bind a function to the <<ListboxSelect>> event. We'll create a separate function for this, and then pull the widget from the event object that is automatically passed to the function.
def print_callback(event):
print_selection(event.widget)
lst.bind("<<ListboxSelect>>", print_callback)
First of all, the reason you are getting an empty tuple is because you have executed the statements:
sel = lst.curselection()
print(sel)
before you have executed the root.mainloop()
Secondly, your setup for listbox fails to include a StringVar variable to hold your list.
Once the variable has been defined, you should be able to use the .insert statements to add your list items one at a time, or you can initialize the StringVar variable using a .set('hy', 'hello', 'hey') command.
To provide a return of a selected variable, you must incorporate an event handler to determine the list position selected onclick or some other triggering method.
For a pretty clear explanation of these characteristics check here
Related
When you want to select an item in a Treeview, you usually use the double-click:
def print_element(event):
print(my_treeview.selection()[0])
my_treeview.bind("<Double-1>", print_element)
Today I tried to do the same but using a single click instead:
my_treeview.bind("<Button-1>", print_element)
But it wouldn't work. The output was just an empty tuple.
I started to search online for an explanation... why is it not working?
EDIT:
My goal was actually to do something every time a treeview item was selected.
I proposed a solution myself using the identify() function of Tkinter
Another user proposed to use the Tkinter callback <ButtonRelease-1> which is much more appropriate
Finally, a third user focused his answer on using the Tkinter callback <<TreeviewSelect>>, which is for sure the best option
The reason it doesn't work the way you expect is because your custom single-click binding happens before the default behavior. So, when your single-click is processed, that happens before an item is selected. The second time you click, your function will print the previously selected item.
If you want to have a function called when an item is selected, you should bind to <<TreeviewSelect>>, which will fire immediately after the user selects an item with a single click or via the keyboard.
The default behavior of a treeview supports selecting multiple items at once, so the following code will print out the text of all of the selected items as a list, even if only a single item is selected. You can, of course, modify this to only print out the first selected item if you so desire.
def print_element(event):
tree = event.widget
selection = [tree.item(item)["text"] for item in tree.selection()]
print("selected items:", selection)
tree.bind("<<TreeviewSelect>>", print_element)
It is because the selection is not set yet when the <Button-1> (it is the same as <ButtonPress-1>, i.e. when the mouse button 1 is pressed and not released) event callback is called.
You should bind on <ButtonRelease-1> or <<TreeviewSelect>> instead as the selection is set when the event callback is being executed.
Why it doesn't work
When you click an item in a treeview, that item is still not in a SELECTED status in the moment the callback is activated. You are changing the status in that very moment.
Using a double-click, the first click change the status, and at the second click you are activating your callback, so the status has already been changed.
How can it work
Kudos to this website
In short,
def print_element(event):
print(my_treeview.identify('item', e.x, e.y))
my_treeview.bind("<Button-1>", print_element)
This time, print_element() will check the coordinates of the mouse, and will discover the selected item check what is under the mouse. Nice and clean!
I have this code:
import tkinter as tk
def onselect(event):
print(event.widget)
root=tk.Tk()
Listbox = tk.Listbox(root)
Listbox2 = tk.Listbox(root)
Listbox.pack(anchor='e', fill='both', expand=True)
Listbox2.pack(anchor='e', fill='both', expand=True)
Listbox.insert('end', 'hello')
Listbox.insert('end', 'bay')
Listbox2.insert('end', 'yes')
Listbox2.insert('end', 'no')
Listbox.bind('<<ListboxSelect>>', onselect)
Listbox2.bind('<<ListboxSelect>>', onselect)
When I select for example any element from the first listbox I get:
.!listbox
But then if I try to select the second listbox I get:
.!listbox2
.!listbox
But I need to get only the second listbox, why is it getting the second and then the first?
How can I fix this?
I need to know what widget I am selecting (it would be better if it could give me the number of the widget: the first listbox 0 the second 1 and so on if more are created).
When you bind to <<ListboxSelect>>, your callback will get called once when the old selection is lost, and a second time when the new selection is made. The event is documented to fire when the selection changes, not just when it is set, and going from the selected state to an unselected state is considered a change.
Here's what's happening:
You select from the first listbox, there is no current selection so your callback is called once.
You select from the second listbox. Since you didn't set exportselection=False, you can only have one thing selected at a time. Therefore your callback will get called for the first listbox when the first listbox loses the selection, and then get called again for the second listbox when the second listbox gets the selection.
I need to know what widget I am selecting
You are given a reference to a widget. You first need to get the selection from that widget. If the selection is empty then it's safe to assume the callback was called because the item was deselected. If the selection is not empty, you can assume that the callback was because the item was selected.
If you want to be able to have something selected from both widgeta, set exportselection to False on both listboxes. Then, when you select something in the second, your callback will only be called once since the other listbox won't lose the selection.
I am new in Python and in tkinter so the question may seems naive: is it ok to create and place widgets at the same time if I don't need to change them?
It works but is it a good practice? And if not why?
An example of what I mean:
import tkinter as tk
window=tk.Tk()
tk.Label(window,text='Lost Label').pack()
window.mainloop()
To expand upon #Skynet's answer....
Whenever you do Widget(*args, **kwargs).pack() the pack() method returns None as would other geometry managers, so if you tried to assign this to a variable the variable would be None.
In this case then probably not, since you probably actually want to be storing the reference to the widget.
If you don't need a reference then there's not really a problem with it. As the other answer notes you don't need a definitve reference to every single widget in your GUI unless you plan to use this reference in some way. Unless I plan on changing the label text / modifying it in someway then I typically use your method to save some space. No need to write more code than you have to!
For example you're creating a Button widget.
btn = Button(blabla, text="Button1")
This returns a button object and if you need later to configure it or get information about it you can do it by through the btn variable.
But if you use something like btn = Button(blabla, text="Button1").pack() it returns None and not a button object so you won't be able to change anything about the button or get information about it later.
Another example is with the Entry widget
entry = Entry(blabla)
Using that later you can do entry.get() to get the text inside the entry
but you won't be able to do it if you use entry = Entry(blabla).pack() since it doesn't return an entry object, it just packs the widget and you won't be able to access it for later use.
There is nothing wrong with that approach and I have already seen it quite a few times. You don't have to keep a reference to every widget in your GUI.
I created a drop-down list using Menubutton from Python Tkinter, but i can't detect which button was pressed ('button-1', 'button-2' or 'button-3')
from Tkinter import *
widget = Frame()
widget.pack()
btnMenu = Menubutton(widget, text='Select action')
contentMenu = Menu(btnMenu)
btnMenu.config(menu=contentMenu)
btnMenu.pack()
btnList = ['button-1', 'button-2', 'button-3']
for btn in btnList:
contentMenu.add_command(label=btn, command=???)
mainloop()
What should i use for "command=" in the string
contentMenu.add_command(label=btn, command=???)
in order to define particular button? Thank you!
What you're looking for is lambda. You can use lambda in your command call like such:
contentMenu.add_command(label=btn, command = lambda btn=btn: buttonClicked(btn))
Then make a method called buttonClicked which would take one argument which would reflect which button has been pressed. Here's a minimal example of what that would look like:
def buttonClicked(btn):
print btn
Ideally though if each button has an entirely different set of execution instructions then they should each get their own method and perhaps you change the list to a tuple of (name, method). This is usually the case for why you would use a menubutton instead of an optionmenu. If you're simply calling the same method for all of them then you might want to consider switching to an optionmenu instead.
I have an Entry widget on a simple calculator. The user can choose to enter an equation via the keypad. I was wondering if there was a way to detect a character(from the keypad in my case) being typed into the Entry widget. So, focus is on the widget, user presses '4', it comes up on the widget... can I detect this act, for basic purposes of logging the input?
Every time you press a key inside a Tkinter window, a Tkinter.Event instance is created. All you need to do is access that instance. Here is a simple script that demonstrates just how:
from Tkinter import Tk, Entry
root = Tk()
def click(key):
# print the key that was pressed
print key.char
entry = Entry()
entry.grid()
# Bind entry to any keypress
entry.bind("<Key>", click)
root.mainloop()
key (being a Tkinter.Event instance) contains many different attributes that can be used to get almost any type of data you want on the key that was pressed. I chose to use the .char attribute here, which will have the script print what each keypress is.
Yes. There are a few different ways to do this, in fact.
You can create a StringVar, attach it to the Entry, and trace it for changes; you can bind all of the relevant events; or you can add a validation command that fires at any of several different points in the sequence. They all do slightly different things.
When a user types 4, there's a key event with just the 4 in it (which doesn't let you distinguish whether the user was adding 4 to the end, or in the middle, or replacing a whole selected word, or…), and then a modification event is fired with the old text,* and then the "key" or "all" validation function is called with the (proposed) new text, and the variable is updated with the (accepted) new text (unless the validation function returned false, in which case the invalidcommand is called instead).
I don't know which one of those you want, so let's show all of them, and you can play around with them and pick the one you want.
import Tkinter as tk
root = tk.Tk()
def validate(newtext):
print('validate: {}'.format(newtext))
return True
vcmd = root.register(validate)
def key(event):
print('key: {}'.format(event.char))
def var(*args):
print('var: {} (args {})'.format(svar.get(), args))
svar = tk.StringVar()
svar.trace('w', var)
entry = tk.Entry(root,
textvariable=svar,
validate="key", validatecommand=(vcmd, '%P'))
entry.bind('<Key>', key)
entry.pack()
root.mainloop()
The syntax for variable trace callbacks is a bit complicated, and not that well documented in Tkinter; if you want to know what the first two arguments mean, you need to read the Tcl/Tk docs, and understand how Tkinter maps your particular StringVar to the Tcl name 'PY_VAR0'… Really, it's a lot easier to just build a separate function for each variable and mode you want to trace, and ignore the args.
The syntax for validation functions is even more complicated, and a lot more flexible than I've shown. For example, you can get the inserted text (which can be more than one character, in case of a paste operation), its position, and all kinds of other things… but none of this is described anywhere in the Tkinter docs, so you will need to go the Tcl/Tk docs. The most common thing you want is the proposed new text as the argument, and for that, use (vcmd, '%P').
Anyway, you should definitely play with doing a variety of different things and see what each mechanism gives you. Move the cursor around or select part of the string before typing, paste with the keyboard and with the mouse, drag and drop the selection, hit a variety of special keys, etc.
* I'm going to ignore this step, because it's different in different versions of Tk, and not very useful anyway. In cases where you really need a modified event, it's probably better to use a Text widget and bind <<Modified>>.
If you just need to do simple things without using trace module you can try
def objchangetext(self, textwidget):
print(textwidget.get()) #print text out to terminal
text1 = tk.Entry(tk.Tk())
text1.bind("<KeyRelease>", lambda event, arg=(0): objchangetext(text1))