Python TK Notebook tab change check - python

Newbie programmer here. I am building a tk based desktop app and ran into an issue:
I have a main window with several stuff in it including two tabs:
global nBook
nBook = ttk.Notebook(self, name="book")
nBook.place(x=300,y=400)
frameOne = ttk.Frame(nBook, width=100, height=100)
frameTwo = ttk.Frame(nBook, width=100, height=100)
nBook.add(frameOne, text='T1')
nBook.add(frameTwo, text='T2')
frameOne.bind("<<NotebookTabChanged>>", self.routine())
frameTwo.bind("<<NotebookTabChanged>>", self.routine())
routine() is a function that SHOULD perform a check every time T2 is selected
def routine(self):
if str(nBook.index(nBook.select())) == "2":
# Do stuff
else:
pass
Problem is that it doesn't do anything when the tab is changed except for calling the routine function as soon as I open the app and never again. I just can't figure out what I'm doing wrong.
Could anyone point out the mistake(s) I'm making?
EDIT: Same issue if I try
nBook.bind("<<NotebookTabChanged>>", self.xbRoutine())

The error comes from the event binding statements: when using self.routine() the callback is called when the bind statement is executed, not when the event is triggered. To get the correct behavior, the second argument of bind should be the name of a function not a call to this function, so simply remove the parentheses.
Another error: when using bind, the callback function is expected to have a first argument (traditionnaly called event) storing the event parameters. So you should define your callback as:
def routine(self, event):
...

I had the same problem. The answer given by #sciroccorics is not complete.
What you bind is not the tab itself, but the notebook.
So, it should be
nBook.bind("<<NotebookTabChanged>>", self.xbRoutine)

Alternatively you could use lambda.
In your case this will look something like this:
frameOne.bind("<<NotebookTabChanged>>", lambda _: self.routine())
Don't forget the _, otherwise you will get a TypeError, since the event is passed as an argument.
lamba is really helpful if your function requires one or more arguments.

Related

in TKInter Why am I getting an error - takes 1 positional argument but 2 were given

Just learning Python and TKInter and have come across this error in my code. Don't know what I'm missing and hoping someone can help. I've included the button code and the function to show you what I have.
def change_font(self):
self.label_name['font'] = "Sawasdee"
self.button1 = Button(self.myframe2, text="Change font")
self.button1.bind("<Button-1>", self.change_font)
When you bind a function to an event, tkinter will call that function with an argument which represents the event which triggered the function to be called. That is why the error says it expected one argument (self) but got two (self, event).
You need to account for that event parameter even if you don't need it. The easiest way is to make it an optional named parameter:
def change_font(self, event=None):
self.label_name["font"] = "Sawasdee"
It's usually incorrect to use bind on a button. The Button widget accepts an attribute named command which can be used to tie the button to a function. In this case, the function will not get the event parameter:
def change_font(self):
self.label_name["font"] = "Sawasdee"
self.button1 = Button(self.myframe2, text="ChangeFont", command=change_font)
The advantage to using command is that it automatically supports not just clicking with the mouse, but also interacting with the button using the keyboard.

How to change label (image form) with next button python

I am currently a novice in python and I'm trying to make a label switch from one image to another by clicking a next button. Here's my code:
from tkinter import *
def next1():
global slide
slide=1
if slide==1:
bglabel.config(image=bg1)
elif slide==2:
bglabel.config(image=bg2)
slide+=1
window.update()
window=Tk()
window.geometry("1500x750+0+0")
bg1=PhotoImage(file="backslide1.png")
bg2=PhotoImage(file="backslide2.png")
nextbutton=PhotoImage(file="next.png")
bglabel=Label(window, image=bg1)
bglabel.place(x=600,y=200)
nextbutton1=Button(window, image=nextbutton, bd=0, command=next1())
window.bind('<Button-1>', next1())
I sat for a good hour or so trying to tamper with the slide variable (trying to declare it before def, removing global, changing value, changing where slide+=1 is, etc) but one of two things always happens; either it's stuck on bg1 with the button clicking but doing nothing, or jumping straight to bg2. I've also tried splitting next1 into two different def's, one for variable tracking, one for switching bglabel, but still the same output. Please help.
(Also, will that window.bind be trouble as I continue to add buttons? If so please let me know how to do it correctly.)
As you mentioned, one 'error' that occurs is that the image immediately jumps to image bg2. This is the line causing that:
nextbutton1=Button(window, image=nextbutton, bd=0, command=next1())
More specifically, where you declare the command associated with the button:
command=next1()
With the enclosed brackets, you're calling the function next1 i.e. as soon as the button is created, run the specified function.
To solve this, just remove the pair of brackets:
nextbutton1=Button(window, image=nextbutton, bd=0, command=next1)
The same goes for your key binding. This way, the button/key now has a reference to the function - it knows what function to run and will run it when the specified action is performed.
More about the key binding...
When you use bind to assign a key to run a function, whatever function that is to be run needs to be made aware as such. Currently, the next function you are trying to bind is given no indication that it can be called using a keyboard button event. To fix that, we set a default parameter in next specifying the event:
def next1(event=None):
#rest of function code here
window.bind('<Button-1>', lambda event: next(event))
Setting a default parameter, event=None, basically means if no value forevent was passed to the function from whatever called it, set it to None by default (in that sense, you can choose to set it to whatever by default). Using lambda for the key bind in this way allows us to pass parameters to functions. We specify what parameter(s) we want to pass to the function and then specify the function, with the parameter(s) enclosed in brackets.
You need to provide the function, not the result of the function. So no parenthesis. Like this:
nextbutton1=Button(window, image=nextbutton, bd=0, command=next1)
Also remove the window.bind line, and your loop logic is broken. "slide" is always 1 since you set that in the function. Are you trying to cycle between the 2 images with every click? If so use itertools.cycle:
from tkinter import *
from itertools import cycle
def next1():
bglabel.config(image=next(bgimages))
window=Tk()
window.geometry("1500x750+0+0")
bg1=PhotoImage(file="backslide1.png")
bg2=PhotoImage(file="backslide2.png")
bgimages = cycle([bg1, bg2])
nextbutton=PhotoImage(file="next.png")
bglabel=Label(window)
bglabel.place(x=600,y=200)
next1() # set the first image
nextbutton1=Button(window, image=nextbutton, bd=0, command=next1)
nextbutton1.pack()
window.mainloop()
(totally untested since i don't have your images).

How to bind all frame widgets to <'Enter'> event

I the following code I want to bind all frame1 items to <'Enter'> Event, but it does not work. I mean canvas.focus_set() does not take effect. How can I solve my problem?
for w in frame1.winfo_children():
w.bind('<Enter>',canvas1.focus_set())
The comment made by Lafexlos actually sends you in the right direction. When you do
w.bind('<Enter>', canvas1.focus_set())
you call canvas1.focus_set() and use the return value of this function call (which is None) to bind to the event. This isn't what you want, because now every time the event is triggered, None is executed instead of canvas1.focus_set().
What you should do is pass a function reference to the bind function. The reference for calling canvas1.focus_set() is canvas1.focus_set. However, using
w.bind('<Enter>', canvas1.focus_set)
still doesn't work.
This is because the bind function passes an event object to the function it has been given, so it will call canvas1.focus_set(event) instead of canvas1.focus_set(). Because focus_set does not accept any arguments, this fails.
You can fix this in two ways. You could make an extra function, which does accept an event object and then calls canvas1.focus_set() without arguments, and then bind the event to this new function. The other option is to use an anonymous "lambda" function to basically do the same like
w.bind('<Enter>', lambda e: canvas1.focus_set())
This way the lambda function accepts the event object as e, but doesn't pass it to focus_set.
P.S. The <Enter> event is not the event that is triggered when you press the Enter button on your keyboard (that is <Return>). The <Enter> event is triggered whenever you move the mouse onto a widget and is accompanied by the <Leave> event for when you leave the widget with your mouse. This might be what you want, but it often leads to confusion.
by using canvas1.bind_all which is the parent of frame1 I solved my problem. Thanks for all solutions.
If there is any mistake I see you making it is likely you are not calling the write command for the Enter key. Hopefully, if you are attempting to do this on windows, you should rather use Return.
More like:
for w in frame1.winfo_children():
w.bind('<Return>',canvas1.focus_set())

TypeError: printName1() takes 0 positional arguments but 1 was given

So I have this very simple thing I wrote and it's killing me trying to figure out why it won't work. All it does it print a statement when you click.
So for the first example I had a button and assigned the function printName1 directly to it, which worked perfectly fine.
Then the next thing was to bind it using the .bind() function. So in this case we just have a frame that prints out certain things based on which button you press. But unfortunately whenever I use bind, it throws the error show above. References tkinter\__init__.py for the error, so it's not something directly in my code but maybe it needs to be done differently? Thanks guys.
from tkinter import *
root = Tk()
def printName1():
print('Jack')
def printName2():
print('John')
def printName3():
print('Jill')
frame = Frame(root, width=300, height=250)
frame.bind("<Button-1>", printName1)
frame.bind("<Button-2>", printName2)
frame.bind("<Button-3>", printName3)
frame.pack()
root.mainloop()
EDIT: The error is confusing because it made it seem like there was an extra argument when there should be 0. But actually I needed to add an argument to the functions and that was event. so it should be def printName1(event) and so on. Just figured I would let you guys know what worked for me in case anyone stumbles upon this.
If you refer to the documentation regarding tkinter events and bindings, you will see that when an event is triggered, the associated event object will be passed as the first (and only) argument to the bounded function (being printName1 and friends in your case).
So what you need to do is to modify those printName* functions to accept the event argument.
def printName1(event):
print('Jack')
Then what you desired to achieve should work.
Naturally, you could make the event argument optional as #TigerhawkT3 suggested.
Events, such as from the keyboard/mouse, are all sent to the application with information about the event: which key was it, where was the mouse when you clicked, that sort of thing. This means that any callback bound to such an event needs to take an argument. If you want to also bind it to a Tkinter Button, which doesn't take an event, you can handle that as well. Just define your functions with a default argument:
def printName1(event=None):
...

Intercepting the close window button (Tkinter window) throws an Tcl error

I have a program that at some point opens a new window (filled with buttons and gizmo's for the user to select and play around with) that is defined as follows:
def window(self,master):
def close(self):
# change some variables
self.destroy()
top = self.top = Toplevel()
# Several lines of buttons
top.lift()
top.protocol("WM_DELETE_WINDOW",close(self))
I initially had a close button there that would wrap everything up nicely but I noticed that if the user used the standard 'X' in the corner of the window, this function obviously would not be called and that would give a lot of problems later on. I found out about the 'WM_DELETE_WINDOW' suggestion from some other questions on this website but it gives me a rather strange error:
File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1630, in wm_protocol
'wm', 'protocol', self._w, name, command)
TclError: bad window path name ".33862072"
I assume that it somehow has gotten the wrong window ID and is unable to catch the event. My question is thus, is that true or not and secondly how should I continue to deal with this issue.
Let's examine this line of code:
top.protocol("WM_DELETE_WINDOW",close(self))
This line of code is saying "immediately call the function close(self), and assign the result to the protocol handler. See the problem? It's immediately calling close, likely before self has been fully constructed. You don't want the function to be called, you want to pass in a reference to the function.
Make close be a method of self (rather than an embedded function) and change the call to top.protocol to look like this (note the lack of trailing parenthesis):
top.protocol("WM_DELETE_WINDOW", self.close)
If you prefer to keep the nested function, you can use lambda:
top.protocol("WM_DELETE_WINDOW", lambda window=self: close(window))

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