I'm trying to write a function to disable a widget in a tkinter program depending on the value of a checkbutton. I want this function to be general: That is, I can pass it the widget and associated check variable and it will disable the widget (if the variable is checked the right way).
Here is an abstracted version of my code
import tkinter
class App:
def __init__(self,root):
widg = tkinter.Scale(root,from_=0,to=100)
checkvar = tkinter.IntVar()
checker = tkinter.Checkbutton(root,variable=checkvar,command=self.check(var,checkvar))
widg.grid()
checker.grid()
widg.configure(state=tkinter.DISABLED)
widg.configure(state=tkinter.NORMAL)
def check(self,widget,var):
if var.get()==1:
widget.configure(state=tkinter.DISABLED)
elif var.get()==0:
widget.configure(state=tkinter.NORMAL)
m = tkinter.Tk()
f=App(m)
It is intended to function such that clicking the checkbutton triggers the callback - check - with the parameters of the widget and the check variable. Then it will evaluate whether the widget should be on or off and change its state accordingly. There are no errors but the state doesn't change. What am I missing here?
Thanks
The command argument simply takes the uncalled function so passing arguments to it takes some workaround.
So it expects self.check rather than self.check() since the widget will call the function later.
I've found that using partial is a workaround for passing the arguments.
import tkinter
from functools import partial
class App:
def __init__(self,root):
widg = tkinter.Scale(root,from_=0,to=100)
checkvar = tkinter.IntVar()
checker = tkinter.Checkbutton(root,variable=checkvar,command=partial(self.check, widg, checkvar))
widg.grid()
checker.grid()
widg.configure(state=tkinter.DISABLED)
widg.configure(state=tkinter.NORMAL)
def check(self,widget,var):
if var.get()==1:
widget.configure(state=tkinter.DISABLED)
elif var.get()==0:
widget.configure(state=tkinter.NORMAL)
m = tkinter.Tk()
f=App(m)
m.mainloop()
Credit to my friend JB for helping me with this.
As user Axe319 suggested, the problem is just that tkinter doesn't expect to pass any parameters. It is possible to work around this by using a lambda function. The line that defines the checker variable, in my original post line 8, can be rewritten as such:
self.checker = tkinter.Checkbutton(root,variable=checkvar,command=lambda:self.check(self.widg,checkvar))
and it will work as intended.
Related
When I call a function from a tkinter widget event I need to add a second parameter in the definition line of the function. Like onChange(self,event) or onChange(self,test). "event" and "test" being the second parameter.
Like:
def onChange(self, test):
print('Content is: ', test.widget.get())
#this also works, but only when having "test" or any other other second parameter name in the def line:
print('Content is: ', self.var.get())
My problem as a beginner in Python/Tkinter is that I do not understand this second parameter and why it is needed. Do anyone have a good explaination of this and/or references to other sources to improve my understanding?
I also would like to understand why this function without the second parameter does not work.
def onChange(self):
print('Content is: ', self.var.get())
A small sample program:
import tkinter as tk
from tkinter import ttk
class GUI:
def __init__(self):
self.window = tk.Tk()
self.create_widgets()
# The following function works with "test" or any other second parameter name in the def line:
def onChange(self, test):
print('Content is: ', test.widget.get())
#this also works, but only when having "test" or any other other second parameter name in the def line:
print('Content is: ', self.var.get())
## The following function does not work:
# def onChange(self):
# print('Content is: ', self.var.get())
def create_widgets(self):
# Makes an Entry widget:
self.string_entry = ttk.Entry(self.window,width=30)
self.string_entry.grid(row=0,column=0)
self.var = tk.StringVar()
self.var.set('Change me and press enter!')
self.string_entry["textvariable"]=self.var
self.string_entry.bind('<Key-Return>', self.onChange)
program = GUI()
program.window.mainloop()
You are allready adding variables that are "extra".
the self variable that you add in the call signature is also a variable that gets filled by the system (python )when calling a class method.
In the same way when an callback is being called by tkinter by the an event, tkinter adds extra variables, in this case the event.
The event variable contains extra information on why the callback is called, this to enable the same callback to be able to handle several different events.
The page http://effbot.org/ is pretty old and is mainly describing Python2 code but it is in most cases update enough to learn about tkinter and how it works.
The Tk framework that calls your function, passes a variable to your callback function (as well as the self variable all methods are called with). When your second method is called it can't accept the second argument so throws a TypeError.
There is more information about the bind methods here.
If you don't care about the argument, you can use the varargs syntax to ignore anything that's passed in.
def onChange(self, *_):
print('Content is: ', self.var.get())
The program works as intended when I simply use tkinter's widgets. When I use ttk's widgets the program repeats itself twice. I tried almost everything in my knowledge to fix this, I believe that *args have something to do with it. Is there anyway to prevent my function _up_options from running twice?
from tkinter import *
from tkinter import ttk
root = Tk()
first = StringVar(root)
second = StringVar(root)
Ore = {'Options': [''], 'Yes': ['One'], 'No': ['Two']}
entry1 = ttk.OptionMenu(root, first, *Ore.keys())
entry2 = ttk.OptionMenu(root, second, '')
entry1.pack()
entry2.pack()
def _up_options(*args):
print('update_options')
ores = Ore[first.get()]
second.set(ores[0])
menu = entry2['menu']
menu.delete(0, 'end')
for line in ores:
print('for')
menu.add_command(label=line, command=lambda choice=line: second.set(choice))
first.trace('w', _up_options)
root.mainloop()
PS, I used *args in my function to work. If anyone can explain this, I would be very grateful
I think I figured this out. The problem is that the variable actually is set twice by the ttk OptionMenu.
Take a look at this piece of code from the tkinter OptionMenu:
for v in values:
menu.add_command(label=v, command=_setit(variable, v, callback))
This adds a button to the menu for each value, with a _setit command. When the _setit is called it sets the variable and another callback if provided:
def __call__(self, *args):
self.__var.set(self.__value)
if self.__callback:
self.__callback(self.__value, *args)
Now look at this piece of code from the ttk OptionMenu:
for val in values:
menu.add_radiobutton(label=val,
command=tkinter._setit(self._variable, val, self._callback),
variable=self._variable)
Instead of a command this adds a radiobutton to the menu. All radiobuttons are "grouped" by linking them to the same variable. Because the radiobuttons have a variable, when one of them is clicked, the variable is set to the value of the button. Next to this, the same command is added as in the tkinter OptionMenu. As said, this sets the variable and then fires another command of provided. As you can see, now the variable is updated twice, once because it is linked to the radiobutton and once more because it is set in the _setit function. Because you trace the changing of the variable and the variable is set twice, your code also runs twice.
Because the variable is set twice from within the ttk code, I guess there's not much you can do about that. If you don't change the variable from any other part of your code than from the OptionMenu though, you could choose to not trace the variable, but instead add your function as command to the OptionMenu:
entry1 = ttk.OptionMenu(root, first, *Ore.keys(), command=_up_options)
P.S. this was introduced with this commit after this bugreport.
I guess when adding the variable=self._variable the command should have been changed to just command=self._callback.
You can understand the problem in the error message:
Exception in Tkinter callback
Traceback (most recent call last):
File "C:\Users\user\AppData\Local\Programs\Python\Python36\lib\tkinter__init__.py", line 1699, in call
return self.func(*args)
TypeError: _up_options() takes 0 positional arguments but 3 were given
Initially, you don't use _up_options When you change the Options you call _up_options to trace the first StringVar and change it to the value of the next object in the dictionary.
Now when you do that you are running on all the objects in the dictionary, therefore, you need the *args so the lambda function will run on all args given!
As for your problem:
When I use ttk's widgets the program repeats itself twice.
EDIT
See #fhdrsdg's answer!
The solution is just to change command=tkinter._setit(self._variable, val, self._callback) to command=self._callback.
Hope you find this helpful!
Instead of tracing the StringVar, add a callback as command argument for OptionMenu constructor.
I created a subclass of ttk.OptionMenu to solve this (as well as to provide slightly simpler usage of the widget and a more useful callback). I think this is a more stable approach than modifying the original class directly or just overriding the original method because it guarantees compatibility with potential changes to the built-in/original widget in future Tkinter versions.
class Dropdown( ttk.OptionMenu ):
def __init__( self, parent, options, default='', variable=None, command=None, **kwargs ):
self.command = command
if not default:
default = options[0]
if not variable:
variable = Tk.StringVar()
if command:
assert callable( command ), 'The given command is not callable! {}'.format( command )
ttk.OptionMenu.__init__( self, parent, variable, default, *options, command=self.callBack, **kwargs )
else:
ttk.OptionMenu.__init__( self, parent, variable, default, *options, **kwargs )
def callBack( self, newValue ):
self.command( self, newValue )
You can then use it like this:
def callback( widget, newValue ):
print 'callback called with', newValue
print 'called by', widget
options = [ 'One', 'Two', 'Three' ]
dropdown = Dropdown( parent, options, command=callback )
dropdown.pack()
Besides avoiding the double-trace issue, other notable differences from the original ttk.OptionMenu includes not needing to supply a Tkinter variable or default value if you don't need them (the default item will be the first item in the options list if not provided), and being able to get the widget that called the callback function when it fires. The latter is very helpful if you have many dropdown widgets sharing the same callback and you need to know which one is being used within the call.
Soon after writing this, I also found another solution using lambda: Passing OptionMenu into a callback (or retrieving a reference to the used widget)
I thought I might still share this Dropdown widget anyway since it can make the higher-level code simpler, and it provides a good base if you have some other custom methods to add in.
I'm trying to get the Entry to widget to clear (clearTextBox()) but also run newQuote(). since I added the second bind it won't clear out. Any ideas?
from random import *
from tkinter import *
def clearTextBox(event):
textBox.delete(0, END)
textBox.insert(0, "")
def newQuote(event):
rightLabel.config(text=quotes[randint(0,10)])
textBox = Entry(leftFrame, width=60)
textBox.pack(ipady=10, side=LEFT)
textBox.bind("<Return>", clearTextBox)
textBox.bind("<Return>", newQuote)
root.mainloop()
Your second call to bind overwrites the first.
To fix this, you can add the keyword argument add="+", to call both functions:
textBox.bind("<Return>", newQuote, add="+")
Hi I've been struggling to get this to work, each time i change something I receive another error. I've been trying to create an entry box with a function and then get the variable from the entry box into a label, created by a button press. When I tried to do this often this error came up.
TypeError: get() missing 1 required positional argument: 'self'
I then put self in in the method brackets.
command = lambda: x.myFunc(self.my_variable.get(self))
Then another error, which I'm not sure how to sort out.
AttributeError: 'My_Class' object has no attribute '_tk'
Here's the full code, I'm new to classes and self, so any corrections are welcome.
from tkinter import *
import time
class My_Class:
def start(self):
self.root=Tk()
self.my_variable=StringVar
self.entry_box=Entry(self.root, textvariable=self.my_variable)
self.entry_box.pack()
self.button=Button(self.root,text="Pass variable now",
command=lambda:x.myFunc(self.my_variable.get(self)))
self.button.pack()
def myFunc(self,my_variable):
self.lab=Label(self.root,text=self.my_variable)
self.lab.pack()
x=My_Class()
x.start()
This is the correct way to create a StringVar object:
text = StringVar() # note additional ()
Can you explain me what x is in the following statement:
lambda: x.myFunc(self.my_variable.get(self))
x is not visible inside the class, because it's declared outside the class.
myFunc is not indented correctly: you should indent it like the __init__ method.
I really recommend you to watch some tutorials on OOP before proceeding. You are basically trying to guess how OOP works.
If you make myFunc A method if the class (which you might be trying to do; it's hard to know because your indentation is wrong), you don't have to pass anything to myFunc. That function has access to everything in the class, so it can get what it needs, when it needs it. That lets you eliminate the use of lambda, which helps reduce complexity.
Also, you normally don't need a StringVar at all, it's just one more thing to keep track of. However, if you really need the label and entry to show exactly the same data, have them share the same textvariable and the text is updated automatically without you having to call a function, or get the value from the widget, or set the value n the label.
Here's an example without using StringVar:
class My_Class:
def start(self):
...
self.entry_box = Entry(self.root)
self.button = Button(..., command = self.myFunc)
...
def myFunc(self):
s = self.entry_box.get()
self.lab = Label(..., text = s)
...
First of all I'm using python 3.3 & 3.2 on windows and Linux respectively.
I am starting to build an rpn calculator. It looks like cross-platform key listeners is a kind of holy grail for python. So far this seems to be doing the trick, but I've created other problems:
I cannot get away from the global variable for entries and using my
stack.
It looks like I have to build the program from inside
callback()
Here is a rough skeleton that shows my direction. Am I missing a way to pass information in and out of callback()
The goal was to build an RPN class before i found myself stuck inside callback().
import tkinter as tk
entry = ""
stack = list()
operators = {"+",
"-",
"*",
"/",
"^",
"sin",
"cos",
"tan"}
def operate(_op):
if _op == "+":
print("plus")
def callback(event):
global entry, stack
entry = entry + event.char
if event.keysym == 'Escape': # exit program
root.destroy()
elif event.keysym=='Return': # push string onto stack TODO
print(entry)
entry = ""
elif entry in operators:
operate(entry)
root = tk.Tk()
root.withdraw()
root.bind('<Key>', callback)
root.mainloop()
You have several options to do what you want to do.
1. Use a Class for your application
The canonical way of doing what you wish without resorting to a global variable is to place the application within a class, and pass a method as a callback (see print_contents) the following is straight from the docs:
class App(Frame):
def __init__(self, master=None):
Frame.__init__(self, master)
self.pack()
self.entrythingy = Entry()
self.entrythingy.pack()
# here is the application variable
self.contents = StringVar()
# set it to some value
self.contents.set("this is a variable")
# tell the entry widget to watch this variable
self.entrythingy["textvariable"] = self.contents
# and here we get a callback when the user hits return.
# we will have the program print out the value of the
# application variable when the user hits return
self.entrythingy.bind('<Key-Return>',
self.print_contents)
def print_contents(self, event):
print("hi. contents of entry is now ---->",
self.contents.get())
2. Curry the callback over your state
You can also use Python's functional programming constructs to curry a function over a global variable and then pass the curried function as a callback.
import functools
global_var = {}
def callback(var, event):
pass
#...
root.bind('<Key>', functools.partial(callback, global_var))
Although this probably isn't what you want.
3. Use a global variable
Sometimes, a global variable is ok.
4. Re-architect for cleanliness and readability
However, you most definitely do not have to build your program inside the callback.
In fact, I would recommend that you create a suite of test with various valid and invalid input, and make a Calculator class or function that takes a string input of RPN commands and returns a value. This is easy to test without a tkinter interface, and will be far more robust.
Then, use your callback to build a string which you pass to your Calculator.
If you want incremental calculation (ie, you're building a simulator), then simply make your Calculator accept single tokens rather than entire equations, but the design remains similar. All the state is then encapsulated inside the Calculator rather than globally.