I am trying to make a simple calculator app using tkinter, but everytime I run the code below i get an error message saying
Traceback (most recent call last):
File "C:\Python33\Lib\site-packages\pythonwin\pywin\framework\scriptutils.py", line 326, in RunScript
exec(codeObject, __main__.__dict__)
File "C:\Users\csp\Python\Calculator App.py", line 17, in <module>
solved = eval(expression)
File "<string>", line 0
^
SyntaxError: unexpected EOF while parsing
CODE:
from tkinter import *
tk = Tk()
tk.title('Calculator')
inp = Entry(tk,text="Enter Expression Here",width=20)
inp.pack()
exit = False
def exitbtn():
global exit
exit = True
return exit
btn = Button(tk,text="Quit?",command=exitbtn)
btn.pack
canvas = Canvas(tk,width=200,height=200)
canvas.pack()
while not exit:
expression = inp.get()
solved = eval(expression)
canvas.create_text(100,100,text=expression,font=('Times', 15))
canvas.create_text(100,150,text=solved,font=('Times', 15))
if exit == True:
break
tk.destroy()
i am really new to Python and dont understand why the "solved = eval(expression)" line wont work. please help
So, the reason why eval is not working is because when you first start your program, expression is just an empty string. If you go to the python shell, and type in eval(''), you'll see the same error appear.
One solution would be to check if expression is an empty string or not, and do something like this:
expression = inp.get()
if expression != '':
solved = eval(expression)
else:
solved = '?'
However, even after you apply this fix, your program won't work, for unrelated reasons. The primary reason is that you never call tk.mainloop() (or whatever it's called), so the window will not show up.
This is because of your while loop -- what you wanted to do was to constantly check the input field and update your canvas whenever you get new input after running it through eval.
However, GUI programs, in general, don't work that way and require a different mindset and approach while writing them. Instead of writing loops to check and update program state, you write functions that will automatically be called whenever the program state changes (which are called events). It'll feel a bit backwards at first, but over time it'll help make your code cleaner and easier to manage.
You're actually already doing this in one part of your program -- with your exitbtn function. Now, you just need to convert your while loop into a similar function and bind it to the Entry object.
EDIT:
Here's some example code that does what you want:
import sys
from tkinter import *
# Create the GUI
tk = Tk()
tk.title('Calculator')
inp = Entry(tk, text="Enter Expression Here", width=20)
inp.pack()
btn = Button(tk, text="Quit?")
btn.pack()
canvas = Canvas(tk, width=200, height=200)
canvas.pack()
# Create callback functions
def end_program(event):
'''Destroys the window and ends the program without needing
to use global variables or a while loop'''
tk.destroy()
sys.exit() # Automatically ends any Python program
def update_canvas(event):
'''Gets the input, tries to eval it, and displays it to the canvas'''
expression = inp.get()
try:
solved = eval(expression)
except SyntaxError:
# The expression wasn't valid, (for example, try typing in "2 +")
# so I defaulted to something else.
solved = '??'
canvas.delete('all') # remove old text to avoid overlapping
canvas.create_text(100, 100, text=expression,font=('Times', 15))
canvas.create_text(100, 150, text=solved,font=('Times', 15))
# Bind callbacks to GUI elements
btn.bind('<Button-1>', end_program)
inp.bind('<KeyRelease>', update_canvas)
# Run the program
tk.mainloop()
Some things to note:
I moved your code for checking inp and writing to the canvas to the update_canvas function, and got rid of the while loop.
The update_canvas function will automatically be called whenever somebody lets go of a key while typing in the inp object (the <KeyRelease> event).
This can cause some problems -- this will mean your update_canvas function will be called while the user is in the process of typing text into your calculator. For example, what if the user types in 2 + 2 *? It's not a complete expression, so can't be parsed by eval.
To solve this, I just wrapped eval in a try-except to prevent any bad input from mucking up the program.
Similarly, end_program will be called whenever somebody left-clicks on the btn object (the <Button-1> event).
Related
I'm trying to overwrite an existing keyboard function on the enter key with a custom hotkey. The problem is, I cannot stop the default action from occurring also. Worse yet, it occurs after the custom action, so I don't have the chance to retroactively correct it as well.
Here are the relevant parts of the code:
from tkinter import *
from tkinter import ttk
from keyboard import *
root = Tk()
root.geometry('400x300')
'''This is the problematic function called by the hotkey'''
def entr_key(text):
'''Enter key results in printing of the line to the right of cursor'''
curs_pos = text.index(INSERT)
right_hand = text.get(curs_pos,END)
right_hand = right_hand.split('\n')[:1] #lines -> strs in a list, selects the first
print (right_hand)
return
'''THIS IS THE MAIN WIDGET FOR THIS FRAME'''
text_view = ttk.Frame(root, padding=10)
text_view.grid()
text_box = Text(text_view, width=45, wrap=WORD)
text_box.grid(column=0, row=1)
text_box.insert('1.0', 'This is a Text widget demo,\nThis text is aimed at testing the enter key function')
add_hotkey("enter", lambda: entr_key(text_box))
root.mainloop()
(I've changed up some variable names to be more understandable, apologies if I missed any but it's not the source of the problem!)
I've also (unsuccesfully) tried other ways of doing this, eg:
while True:
if is_pressed('enter'):
entr_key(text_box)
'''AND ALSO'''
on_press_key("enter", lambda x=None: entr_key(text_box))
Just to be clear, I don't want the default action of enter key moving the text to a new line.
I need either a way to "break" the key event so that only the custom action takes place, or a way for the custom action to occur after default action, so I can retroactively edit it out
EDIT!!!
I've found a workaround: at the start of entr_key() I call time.sleep(0.01). During this, the default action of the enter key occurs first, and I can retroactively edit it out when the custom function resumes. The delay is slight enough to not be noticeable at all.
But still, if anyone knows how to prevent the default action from occurring completely, I would really appreciate it.
It's the whole day I'm trying to solve this ridiculous problem, but without success; in this forum there is a lot of material, but usually they are enormous amounts of code and I cannot understand what's going on. On the internet they generally suggest casting but it doesn't work. To make things easy I wrote a sample code to illustrate the issues I'm having in a bigger code
import tkinter as tk
from tkinter import *
#from tkinter import ttk
my_window = tk.Tk()
my_label = tk.Label(master=my_window,text="N")
my_label.pack()
my_entry = tk.Entry(master=my_window)
my_entry.pack()
N = my_entry.get()
print(float(N))
my_window.mainloop()
Very nice and simple, but I get the following message
ValueError: could not convert string to float: ''
I tried many possibilities, but anything worked. Any little suggestion is very much appreciated. Thanks
Edit:
I want to understand how to assign float(N) to a global variable, say a, so I can use it later on in the code, and I just took the code of #Cool Cloud and modified it a little
import tkinter as tk
from tkinter import *
my_window = tk.Tk()
a=1.
def cast():
N = my_entry.get()
try: # Try to execute this
print(float(N))
a=float(N)
except ValueError: # If ValueError(meaning it is not a float) is triggered then print...
print('Not a number!')
my_label = tk.Label(master=my_window,text="N")
my_label.pack()
my_entry = tk.Entry(master=my_window)
my_entry.pack()
# N = my_entry.get() N will be empty as my_entry is empty when code is executed
Button(my_window,text='Click me to convert to
float',command=cast).pack() # A button to trigger event
print(a)
my_window.mainloop()
The output of this is in the following image
As you can see it directly prints 1.0 without waiting for the assignment a=float(N), so my doubt is how can I actually do this assignment, to use it later in my code. Thanks
P.S.: I understand that print(a) inside the definition of cast() would give correctly 123.0 in this case, but my problem is more general: I'm trying to understand how to entry an N value, making it float and "propagate" it to the rest of the program. My doubt is given by the fact that print(a) almost at the very last line of the program, and still doesn't wait for cast() to come in.
GUI programming is event driven, which means you will have to code based on events triggered. Every python code runs from top to bottom, and in this case all the code from top to bottom, outside functions, is executed. That means as soon as:
my_entry = tk.Entry(master=my_window)
my_entry.pack()
...is executed, the next line to be executed is N = my_entry.get(), and at the time of execution there is NOTHING inside the entry widget and hence N becomes empty string, and then you are trying to convert that empty string to a float, which will obviously give an error.
What you should be doing is, make a button and when you click it(event is triggered) and connect it to a function that will get the input and convert to float. So that when you click the button you have entered something onto the entry and now it is no longer empty.
import tkinter as tk
from tkinter import *
my_window = tk.Tk()
def cast():
N = my_entry.get()
try: # Try to execute this
print(float(N))
except ValueError: # If ValueError(meaning it is not a float) is triggered then print...
print('Not a number!')
my_label = tk.Label(master=my_window,text="N")
my_label.pack()
my_entry = tk.Entry(master=my_window)
my_entry.pack()
# N = my_entry.get() N will be empty as my_entry is empty when code is executed
Button(my_window,text='Click me to convert to float',command=cast).pack() # A button to trigger event
my_window.mainloop()
Another way, and an unpopular way, is to use DoubleVar() which will get() the text for you, in this case, your entry will accept any value but when you get() the value from the DoubleVar() it will raise a TclError if it is not a float.
def cast():
# Unlike before, error will be generated at get() and you dont need float()
# because if there is no error then it is guaranteed to be a float anyway
try:
N = var.get()
print(N)
except TclError: # If TclError is triggered then print...
print('Not a number!')
var = DoubleVar() # tkinter control variable
my_entry = tk.Entry(master=my_window,textvariable=var)
my_entry.pack()
Note: You can do my_entry.get() and it wont give any error even if the input is not a float, error comes only in the case of var.get().
From:https://www.geeksforgeeks.org/python-tkinter-entry-widget/
"get() : Returns the entry’s current text as a string."
I think that you can't just convert string to float.
So, essentially what is going on is I made a password manager that had a password generation part to it, I moved it to a windowed Tkinter program for ease of use. I got everything down except for the check box, so at first when the function was called it would give me the error that alphabet had empty length so I set alphabet equal to the list with special characters. After that I tried them with while loops, same result. (this whole code is a function inside the program that only gets ran when a button is pressed) I know I could probably fix this issue with the init but I was hoping if anyone knew an easier way without rewriting too much. Here is the edit to make the code simplified. I used it with a while loop, and got the same result as the if statement. I get the error that a is not defined in this situation.
from tkinter import *
import random
def cbox_var():
while cbox_1 == True:
a = 10
while cbox_1 == False:
a = 20
print(a)
main = Tk()
cbox_1 = Checkbutton(main, text="yes or no")
cbox_1.pack()
testbutton = Button(main,text="Test", command=cbox_var)
testbutton.pack()
main.mainloop()
To get the value of a checkbutton you must assign one of the special tkinter variables to it. You can then get the value by calling the get method on the variable.
Example:
import tkinter as tk
def cbox_var():
checked = cbox_variable.get()
print("Checked?", checked)
main = tk.Tk()
cbox_variable = tk.BooleanVar()
cbox_1 = tk.Checkbutton(main, variable=cbox_variable, text="yes or no")
cbox_1.pack()
testbutton = tk.Button(main,text="Test", command=cbox_var)
testbutton.pack()
main.mainloop()
all. I'm working on a simple Notepad-like program that saves files and closes the program when the escape key is pressed. I mention this because it is in this method that the program runs into problems. textpad is a ScrolledText object.
This line:
`contents = self.textPad.get(self, 1.0, END)`
results in the following error:
Exception in Tkinter callback
Traceback (most recent call last):
File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1535, in __call__
return self.func(*args)
File "todopad.py", line 24, in save_and_quit
contents = self.textPad.get(self, 1.0, END)
AttributeError: Event instance has no attribute 'textPad'
I know this is the problem, because the program executes and terminates without issue when this line is commented out. Although I don't understand the error at all.
This has been a very long-winded way of asking: How can I retrieve the contents of a ScrolledText text pad and save it to a variable or directly write it to a file? And also an explanation about the error message?
Thank you in advance.
EDIT: As requested, here is the code for the entire thing.
import sys
import Tkinter
from Tkinter import *
from ScrolledText import *
root = Tkinter.Tk(className = "TodoPad");
textPad = ScrolledText(root, width = 80, height = 20)
def start_and_open():
textFile = open('/home/colin/documents/prog/py/todopad/todo', 'r')
contents = textFile.read()
textPad.insert('1.0', contents)
textFile.close()
def save_and_quit(self):
textFile = open('/home/colin/documents/prog/py/todopad/todo', 'w')
#contents = self.textPad.get(self, 1.0, END) # The line in question
#textFile.write(contents)
textFile.close()
root.destroy()
textPad.pack()
root.bind('<Escape>', save_and_quit)
root.after(1, start_and_open)
root.mainloop()
Since I have posted the whole thing I may as well explain the rationale behind everything. It's supposed to be a fast little thing that opens a to-do list and displays what's already on the list in the text box. I make whatever edits I like, then it saves before closing when I hit escape, problem being is that it doesn't like closing because of the line that I mentioned previously in my post.
First of all, kudos on identifying the problem.
Placing the Widget
To answer what is going wrong: you need to actually place the widget into the window frame. You have a choice between .grid() and .pack(). The first allows you to pick exactly where you want it to go, the second puts in a (technically) default location.
Right now, the instance of your widget is not preset, so your program has no idea where to pull the value from. You have to set a location. i would recommend using .grid(), but for the example .pack() will work as well.
textPad = ScrolledText(root, width = 80, height = 20)
textPad.pack()
Try this, and see if it works. This should fix it, but I could be wrong.
Do NOT just do
textPad = ScrolledText(root, width = 80, height = 20).pack()
The pack() function returns a NULL and will nullify your widget.
Your Issue With Self
Finally, why are you using self at all? You are not using any classes--you need to globalize the variable. The error that is thrown is a result of your program not knowing what class you are pulling the self instance from. Remove the self variables from the program, and put this into the function:
global textPad
This will make it global and all functions will be able to use it.
This should solve all the problems you have right now. However, give it a try and report what happens.
Here are some resources on global variables, getting input from widgets, and saving to files;
http://www.python-course.eu/python3_global_vs_local_variables.php
http://effbot.org/tkinterbook/text.htm
http://www.afterhoursprogramming.com/tutorial/Python/Writing-to-Files/
Happy coding, and best of luck!!
As part of my program I ask the user for their name and class (high school class). Once the user presses 'Enter' after typing their name the button is disabled and the 'tutor' field appears. However, the user is in essence able to submit their name even if they haven't typed anything. I only want the 'Enter' button to be active once the user has started typing.
What I have done below doesn't seem to work :(
Also, my input validation doesn't work - know why?
class Enter_Name_Window(tk.Toplevel):
'''A simple instruction window'''
def __init__(self, parent):
tk.Toplevel.__init__(self, parent)
self.text = tk.Label(self, width=40, height=2, text= "Please enter your name and class." )
self.text.pack(side="top", fill="both", expand=True)
name_var = StringVar()
def validate_enter_0():
self.Enter_0.config(state=(NORMAL if name_var.get() else DISABLED))
print("validate enter worked")
name_var.trace('w', lambda name, index, mode: validate_enter_0)
enter_name = Entry(self, textvariable=name_var)
enter_name.pack()
enter_name.focus_set()
def callback():
if len(name_var) > 10 or any(l not in string.ascii_letters for l in name_var):
print("Input validation worked")
self.display_name = tk.Label(self, width=40, height=2, text = "Now please enter your tutor group.")
self.display_name.pack(side="top", fill="both", expand=True)
tutor_var = StringVar()
def validate_enter_2():
self.Enter_0_2.config(state=(NORMAL if tutor_var.get() else DISABLED))
print("validate enter worked")
tutor_var.trace('w', lambda name, index, mode: validate_enter_0_2)
tutor = Entry(self, textvariable=tutor_var)
tutor.pack()
tutor.focus_set()
self.Enter_0.config(state="disabled")
self.Enter_0_2 = Button(self, text="Enter", width=10, command=self.destroy)
self.Enter_0_2.pack()
self.Enter_0 = Button(self, text="Enter", width=10, command=callback)
self.Enter_0.pack()
The first obvious problem is this line:
tutor_var.trace('w', lambda name, index, mode: validate_enter_0_2)
You've created a function that takes three variables, and returns the validate_enter_0_2 function as a function object. That doesn't do any good.
You want to create a function that calls the validate_enter_0_2 function. Like this:
tutor_var.trace('w', lambda name, index, mode: validate_enter_0_2())
You have the exact same problem with name_var and will also need to fix it there, of course.
On top of that, you don't actually have a function named validate_enter_0_2 to call, because you defined it as validate_enter_2. This means your validation function just raises a NameError instead of doing useful. Or, if you have a validate_enter_2 function defined somewhere else in your code, it calls the wrong function. (This is one reason that cryptic names like enter_0_2 and enter_2 are not a good thing.)
There's at least one other problem with your code: You're repeatedly trying to use name_var, which is a StringVar object, as if it were a string. You can't do that. And if you actually look at the console output, Tkinter will tell you this, with tracebacks like this:
Exception in Tkinter callback
Traceback (most recent call last):
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk/Tkinter.py", line 1410, in __call__
return self.func(*args)
File "tkval2.py", line 25, in callback
if len(name_var) > 10 or any(l not in string.ascii_letters for l in name_var):
AttributeError: StringVar instance has no attribute '__len__'
And that exception is happening before you get a chance to create the new Entry.
To fix that, you need to call get on the StringVar whenever you want to get its value, like this:
if len(name_var.get()) > 10 or any(l not in string.ascii_letters for l in name_var.get())
Finally, as I explained in the answer to your other question, your trace validator isn't going to get called until something changes. This means you will either need to call it explicitly, or explicitly name_var.set(''), or just start the button off disabled. As written, it will start off enabled, and only disable if you type something and then erase it.
I'm not sure whether those are the only problems with your code, but all of them will certainly prevent your validation from working as expected. So, you need to fix all of them, and any other errors in your code, before it will work.
From your comments:
I am however wondering how to create a pop up message displaying an error…
When do you want to do that? What condition do you want to check, and when do you want to check it?
At any rate, as in most GUIs, the way to "pop up" anything like this is a dialog. Dialog Windows in the Tkinter book explains everything you need to know. But you don't need to copy-paste all that code, or write it from scratch; the stdlib comes with Tkinter helper modules that do most of the work for you. In your case, you probably just want tkMessageBox.
… and something that forces the user to re enter their name
Force them how? Just erasing the existing Entry contents would leave them with an empty box to fill in, which would also disable the button. Is that what you want?
Anyway, guessing at what you want, it could look something like this:
def callback():
if len(name_var.get()) > 10:
tkMessageBox.showerror("Bad name", "Your name is too long. What's wrong with good American names like Joe?")
name_var.set('')
return
# the rest of your code here
In the callback function (called when they click the button after typing their name), instead of just checking some condition and printing something out, I check a condition and pop up an error dialog, clear out the existing name, and return early instead of creating the second half of the form. I didn't handle your other condition (any non-ASCII letters), but it should be obvious how to add that.
However, validation like this might be better done through actual validation—instead of making them wait until they click the button, catch it as soon as they try to type the 11th character, or a space or accented character, or whatever else you don't like. Then you can pop up a message box, and either disable the button until they fix it, reject/undo the change (which is easier with a validatecommand function than with a trace function, as shown in my answer to your previous question).
One last thing: Instead of a message box, it may be better to just embed the error as, say, a Label that appears in the form itself (maybe with the error description in red, with a big flag icon). This is common in web apps and in more modern GUIs because it provides more immediate feedback, and is less obtrusive to the user flow.