So I've been trying to get into using classes in my tkinter projects, but I seem to have trouble understanding exactly how classes interact. Especially when tkinter is involved. I can accesses variables and values and pass those around, but I can't seem to figure out how to do triggers.
My current problem is with trying to trigger an event from a different class.
A simple version of the problem is this:
from tkinter import *
class Area:
def __init__(self):
self.can = Canvas(width=100, height=100, bg="green")
self.can.pack(in_=window)
self.can.bind("<Button-3>", self.test)
self.square = self.can.create_rectangle(25, 25, 75, 75)
def test(self, event):
self.can.delete("all")
class Trigger:
def __init__(self):
self.button = Button(text="click me", command=?)
self.button.pack(in_=window)
window = Tk()
Area()
Trigger()
window.mainloop()
It creates a green canvas with a square in the middle. When you right click the canvas, the square is removed. I then try to trigger that same behavior from a different class, demonstrated here with a button.
Problem is, I can't for the life of me figure out what to have as a command on the button.
I've tried command=Area.test, but then I get "
TypeError: test() missing 2 required positional arguments: 'self' and
'event'"
I've tried command=Area.test(Area, "event") and command=Area.test(self, "event"), but they return:
AttributeError: type object 'Area' has no attribute 'can'
and
AttributeError: type object 'Area' has no attribute 'can'
I also tried Area().test("event), which gave no error but gave me 2 instances of the canvas, one with the square and one without. The button did nothing then.
Looked into inheritance, so I tried that by putting Area as inheritance on the Trigger class, then do command=self.test("event")
But then got:
AttributeError: 'Trigger' object has no attribute 'can'
So I'm out of ideas.. Am I doing the __init__part wrong?
First, if you want to use a function both as a target of an event and as the value for a command attribute, you should make the event argument optional. You can do that by giving it a default value of None:
def test(self, event=None):
self.can.delete("all")
Second, the Trigger object needs to be given the instance of the Area object so that it can call methods on that object. There are several ways to do this, but the most straight-forward is to pass it in when creating the object. This means you need to modify Trigger.__init__ to accept the parameter, and then you need to pass it in when creating the object.
This is how to modify the __init__ method:
class Trigger:
def __init__(self, area):
self.button = Button(text="click me", command=area.test)
self.button.pack(in_=window)
This is how to pass the Area object to the Trigger object:
area=Area()
Trigger(area)
Related
I am trying to condense my code, so I want to create object instead of having to create labels each time I need one.
However, I can't figure out how to be able to change attributes of the object-labels using .config. I've tried using objectvariable.config(...), but that doesn't work. Neither does using a method like in the following:
class title_label():
def __init__(self):
self = tkinter.Label(root)
self.pack(side='left')
def update(self, text):
self.config(text=text)
Error-message is: objectvariable object has no attribute config.
How can I use .config on an object containing a label?
It should be
class title_label():
def __init__(self, root):
self.label = tkinter.Label(root) # <<< 'label' field here
self.label.pack(side='left')
def update(self, text):
self.label.config(text=text)
self hold the reference to the class itself. label is something that your class is supposed to hold not to be. Another approach would be to derive from the Label class, but for what it is worth storing the label in the field should be good enough for you.
If you made your class a subclass of tkinter.Label then it would have inherited a config() method from it.
Here's an example of how that might be done:
import tkinter as tk
class TitleLabel(tk.Label):
def update(self, text):
self.config(text=text)
if __name__ == '__main__':
root = tk.Tk()
title_lbl = TitleLabel(root, text='Initial Text')
title_lbl.pack(side='left')
root.after(1000, lambda: title_lbl.update('CHANGED!')) # Update after 1 sec.
root.mainloop()
But as you can see, there wouldn't really be much point of doing so, since the only thing update() does is forward to call on the base class.
Inspired by this 300+ vote closed Q&A: Best way to structure a tkinter application?, I'm looking to avoid explicitly using root in a function within a class. I think it should be implicitly declared through self or parent or something like that. Here is the code in question:
I have this code...
self.label_this = tk.StringVar()
self.label_last = tk.StringVar()
self.label_total = tk.StringVar()
tk.Label(count_frame, textvariable=self.label_this, \
font=(None, MON_FONTSIZE)).pack(anchor=tk.W)
tk.Label(count_frame, textvariable=self.label_last, \
font=(None, MON_FONTSIZE)).pack(anchor=tk.W)
tk.Label(count_frame, textvariable=self.label_total, \
font=(None, MON_FONTSIZE)).pack(anchor=tk.W)
self.update_cnt_labels()
Then later on...
''' Get list of Window ID's on monitor now '''
new_windows = self.windows_on_monitor(new_windows)
new_windows_cnt = len(new_windows) / WIN_CNT
if self.old_windows_cnt == new_windows_cnt :
FlashMessage (self.label_this, "No new windows to remove...", \
3, 750, 250)
self.update_cnt_labels()
return
Then later on...
class FlashMessage:
def __init__(self, widget, message, count=5, on=500, off=300):
self.delay_show (1, widget, message)
for i in range(count):
self.delay_show (on, widget, "")
self.delay_show (off, widget, message)
def delay_show(self, ms, widget, message):
root.after(ms, widget.set(message))
root.update_idletasks()
I want to avoid using root in the last two lines and use self or something similar.
My program call chain is something like:
the traditional: root = tk.Tk()
bunch of mainline initialization stuff.
the class: ResizingCanvas(mycanvas)
mainline function: popup(event) which is bound to <ButtonPress-1>
Dynamically formatted menu.tk_popup(event.x_root, event.y_root)
the class: RemoveNewWindows()
the function: remove()
the class: FlashMessage() (show above)
the function: self.delay_show() (shown above)
Each class and function has haphazard self, positional parameters, *args and **kwargs which mostly serve no purpose. Indeed even the __init__ above might be unnecessary. This is a result of copying code all over stack overflow.
Every second word in the program seems to be self but the word parent is only used in the class ResizingCanvas(). Do I have to propagate parent down the call list and use it somehow?
You can call after and update_idletasks on any widget. There are many such functions that can be called on any widget but which have a global effect.
In your case, you'll need to pass some widget into the FlashMessage constructor and save the reference. You can then use the reference to call the functions.
You're passing something called widget that doesn't actually contain a widget. You need to rename it to something more appropriate (eg: var), and then pass in an actual widget.
(Note: you also are calling after incorrectly, which I've fixed in the following example)
For example:
class FlashMessage:
def __init__(self, widget, var, message, count=5, on=500, off=300):
self.widget = widget
...
def delay_show(self, ...):
self.widget.after(ms, var.set, message)
self.widget.update_idletasks()
Then, whenever you create an instance of FlashMessage you need to add a widget as the first parameter.
For example, assuming that count_frame is defined in the context where you create an instance of FlashMessage and it is an actual widget, it might look something like this:
if self.old_windows_cnt == new_windows_cnt :
FlashMessage (count_frame, self.label_this, "No new windows to remove...", \
3, 750, 250)
self.update_cnt_labels()
return
I am trying to create a simple timer in Python and am aiming to build the user interface using classes. I would like to use the classes to initialise user interface. Then in the main text of the body, I would like to add attributes using the .grid and .configure methods. But when I try to do this, the error: 'statInter' object has no attribute 'tk' appears.
I am a beginner in programming, but if I understand the error correctly the it results because the .grid and other Button methods are not inherited by my statInter (i.e. static interface) class. Is this correct? How do I solve this error? I trued inheriting the properties of Button class and even Tk class, but in the later case I get an infinite loop i.e. maximum recursion depth exceeded.
Thanks for your help
#This is a simple timer version
from tkinter import *
window = Tk()
window.title('Tea timer')
window.minsize(300,100)
window.resizable(0,0)
class statInter(Button,Entry):
def __init__(self, posx, posy):
self.posx = posx # So the variables inside the class are defined broadly
self.posy = posy
def button(self):
Button(window).grid(row=self.posx, column=self.posy)
def field(self):
Entry(window, width=5)
sth = statInter(1,2)
sth.grid(row=1, column = 2)
window.mainloop()
The problem is your derived StatInter class (CamelCasing the class name as suggested in PEP 8 - Style Guide for Python Code) doesn't initialize its base classes, which generally doesn't happen implicitly in Python (as it does in say, C++).
In order to do that from within the StatInter.__init__() method, you're going to need to know the parent widget that will contain it (all widgets except the top level window are contained in a hierarchy) — so an extra argument needs to be passed to the derived class's constructor so it can be passed on to each of the base class constructors.
You haven't encountered another problem yet, but likely will soon. To avoid it, you're also going to have explicitly pass self when explicitly calling the base class methods in button() and field().
from tkinter import *
window = Tk()
window.title('Tea timer')
window.minsize(300,100)
window.resizable(0,0)
class StatInter(Button, Entry):
def __init__(self, parent, posx, posy): # Added parent argument
Button.__init__(self, parent) # Explicit call to base class
Entry.__init__(self, parent) # Explicit call to base class
self.posx = posx # So the variables inside the class are defined broadly
self.posy = posy
def button(self):
Button.grid(self, row=self.posx, column=self.posy) # Add self
def field(self):
Entry.config(self, width=5) # Add self
sth = StatInter(window, 1, 2) # Add parent argument to call
sth.grid(row=1, column=2)
window.mainloop()
The reason you get this error is because you never invoke either of the constructors from the classes you're inheriting from (either Button or Entry).
If you change your __init__ to be:
def __init__(self, posx, posy):
Button.__init__(self)
self.posx = posx # So the variables inside the class are defined broadly
self.posy = posy
Then you won't get the error you were having previously, and a little window pops up. In the new __init__, we explicitly invoke Button's constructor.
Unlike Java and some other languages, the super constructor is NOT invoked by default. I assume that each class inheriting from other tkinter classes must have a tk field. By invoking the parent constructor of your choice, this field will be created. If you don't invoke a parent constructor, though, then this will not be an established field, and you'll get the error you have described ('statInter' object has no attribute 'tk').
HTH!
I'm a beginner at Python and I'm currently on chapter 10/12 in my book 'Python Programming for the absolute beginner'. I understand OOP in Python but due to one chapter (which discusses some relevant information about OOP) being based around a program for playing 'Cards' I had to skip part of the chapter (because I don't know how to play Cards) and so I missed out on important information which I should know at this point in the book. The reason I'm saying this is because I will need a simple answer to my question because complex answers may be too difficult for me to interpret.
But anyway here is my problem, there is a piece of a code in my book which creates a simple GUI program (which I completely understand) and then there's an Object Oriented version of the program which I do not understand (main parts highlighted in '##'s). It contains something called a 'Superclass constructor' which completely confused me (I tried doing some research on it, but it just didn't make sense to me). If anyone can help explain to me how the second version of the code works (or give helpful resources) then I will be highly grateful:
First version of the code:
from tkinter import *
# create a root window
root = Tk()
root.title("Lazy Buttons")
root.geometry("200x85")
app = Frame(root)
app.grid()
bttn1 = Button(app, text = "This is a button")
bttn1.grid()
root.mainloop()
Second version:
from tkinter import *
class Application(Frame):
def __init__(self, master): # Why is 'master' called?
super(Application, self).__init__(master) # ?
self.grid()
self.create_widgets()
def create_widgets(self):
self.bttn1 = Button(self, text = "This is a button")
self.bttn1.grid()
root = Tk()
root.title("Lazy Buttons 2")
root.geometry("200x85")
app = Application(root)
root.mainloop()
Don't skip parts of a tutorial because you don't know the problem domain - you don't need to know how to play cards to understand how card game code relates to what the program does. To your actual problem:
class Application(**Frame**):
This creates a class Application that inherits from a class Frame. If you don't know inheritance, the tutorial you're following should explain it, or you could try this introduction to classes and inheritance that I just googled up.
**def __init__(self, master):
This creates a method, with the name __init__. This is a special method in Python, which behaves similarly to a constructor in other languages - essentially, whenever an Application is created, Python will immediately call its __init__ method before it gives the new object back to whoever made it. master is just an argument, same as any other to any other function.
super(Application, self).__init__(master)
This calls the constructor of the superclass, to let it initialise the new object. super(Application, self) figures out what the superclass is (in this case it is Frame; in more complex cases that you will come to eventually, this is harder to work out and super's magic becomes important).
self.create_widgets()**
This calls the method create_widgets, which you define below this. The object before the . gets passed into the method as the first argument, self - so, this calls a different method on the same object that the method you're in has been called on.
app = Application(root)
This creates an Application - objects are created by calling the class, like how list() creates a list. The argument you pass in gets handed to __init__ as its second argument (the new Application that Python creates behind the scenes gets passed as the first argument, self, as above). Python creates a new Application, calls its __init__ for you, and then assigns the new object to the name 'app'.
'super' part here is only to properly call constructor of base class (the class you are inheriting from.)
Let's consider following example:
class Device(): # class representing some drawing device
...
def fill(self, color)
... # actual code for draw on this device
screen = Device()
WHITE_COLOR = (255, 255, 255)
class Window(object):
def __init__(self, width, height):
self.width = width
self.height = height
def area(self):
return self.width * self.height
class ColoredWindow(Window):
def __init__(width, height, color):
super(ColoredWindow, self).__init__(width, height)
self.color = color
def fill(self):
screen.fill(self.width, self.height, self.color)
my_window = ColoredWindow(640, 480, WHITE_COLOR)
my_window.fill()
The first class here, Window, is a generic window that has width and height attributes that are passed in constructor.
ColoredWindow is a subscass of Window, it has additional attribute color.
When ColoredWindow is constructed, it needs somehow pass width and height parameters to its baseclass Window.
This is exactly what construction super(ColoredWindow, self).__init__(width, height) is for. The first part, super(ColoredWindow, self), returns a reference to baseclass (Window in our case), and second part, __init__(width, height), just calls its constructor with right parameters.
In your example master is not called, it's just parameter to __init__ method of Application class.
One question: How do you dynamically draw to a Tkinter Canvas object from a button click?
This topic was posted originally by user339860 (see 1) as a two part question, but the second portion of the question has not yet been addressed. I'm experiencing the same problem, specifically I cannot draw to a Canvas object from a button event. Getting this question answered will help two people, myself and user339860; please take a look.
The application creates two frames positioned left and right, the second frame contains the Canvas object. I have a button in the first frame bound to a function/method named drawRectangle. The application runs fine, it even draws a rectangle in the Canvas object using the create_rectangle method, until you click the button. When you click the button you get a message with the following;
tkinter_app_27Nov2010.py", line 25, in drawRectangle
self.myCan.create_rectangle(64,64,110,110,fill='blue')
AttributeError: 'NoneType' object has no attribute 'create_rectangle'
I thought it might have something to do with the scope of the Canvas object, so I created a class level variable set to None, but that didn't fix the issue. I thought about the Canvas display list (see 2), but the Tk manual pages don't reflect a method of adding a new object that I could find.
CODE:
# tkinter_app_27Nov2010.py
from Tkinter import *
class Application(Frame):
myCan = None
def createWidgets(self):
uiFrame = Frame(self,width=300,height=30)
uiFrame.configure(background='#e0e0e0')
uiFrame.grid(row=0,column=0,sticky=N+S)
outputFrame = Frame(self,width=300,height=300,background='#C0C0C0')
outputFrame.grid(row=0,column=1)
newBtn = Button(uiFrame,text="testing",command=self.drawRectangle)
newBtn.grid(row=0,column=0)
fillLbl = Label(uiFrame,text='-').grid(row=1,sticky=N+S)
newLBL = Label(outputFrame,text="another testing",background='#C0C0C0')
newLBL.grid(row=0)
myCan = Canvas(outputFrame,width=300,height=300,borderwidth=1,relief='sunken')
myCan.grid(row=1)
myCan.create_rectangle(34,34,50,50,fill='red')
def drawRectangle(self):
self.myCan.create_rectangle(64,64,110,110,fill='blue')
def __init__(self,master):
Frame.__init__(self,master)
self.pack()
self.createWidgets()
root = Tk()
myApp = Application(master=root)
root.title("Tkinter Testing!")
myApp.mainloop()
There has to be a way to get a handle on the "damage/repair display model" (see 3) the Tkinter Canvas object uses to update itself. Please help!
References:
stackoverflow.com/questions/2824041/dynamically-add-items-to-tkinter-canvas
www.tcl.tk/man/tcl8.4/TkCmd/canvas.htm#M16
effbot.org/tkinterbook/canvas.htm#performance-issues
This is a Python problem, not a tkinter one. You have defined local variables inside createWidgets, but you haven't set them as instance attributes. You need to use self.foo for that:
>>> class Foo:
... def __init__(self):
... bar = "baz"
...
>>> class Bar:
... def __init__(self):
... self.bar = "baz"
...
>>> foo = Foo()
>>> foo.bar
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: Foo instance has no attribute 'bar'
>>> bar = Bar()
>>> bar.bar
'baz'
Notice that you are indeed correct: the problem is to do with the scope of the Canvas. Or more precisely, with the scope of the myCan variable. If you hadn't defined the class variable myCan, the lookup self.myCan would have raised a revealing AttributeError.
There is no object "self.myCan". You have to create it as a canvas object or whatever before you can use it. You may also have to call update_idletasks() depending on what you do.