Why am I getting a "bad window path name" error when trying to add a label widget to the s-CodePudding

I'm creating a homework planner program using Tkinter, and I've run into a problem when trying to add an error label to the screen to show the user that they might have entered a duplicate assignment. Here's the constructor for the label (entFrame is where I put the user entries):

duplicateLabel = Label(entFrame, text="Warning: the entered assignment is a duplicate!", bg=bgColor, font=regularFont)

When a user submits an assignment, a function runs that creates a new assignment object. In that function, I call a method of the assignment to check if it is a duplicate. In that method, I create a list of all the lines of a csv file where I store the assignments. Then, I check the new assignment's attributes to some of the stored attributes of previous assignments. If the conditional is true, I add the warning label to the screen. Otherwise, I try to destroy the label to remove it from the screen to get rid of a previous warning from an old assignment.

    def checkDuplicates(self):
        contents = []
        file = open("homeworkAssets/assignmentsFile", "r")
        for content in csv.reader(file):
            contents.append(content)
        file.close()
        for assignment in contents:
            if self.course == assignment[1] and self.dueDate == assignment[2] and self.details == assignment[3]:
                duplicateLabel.grid(row=0, column=0, columnspan=2)
            else:
                duplicateLabel.destroy()

My first thought was that the .destroy() method was deleting the Label object, although when I added a print statement after that last line, the console read: .!labelframe.!labelframe.!label6 which I assume means it hasn't been deleted. When I run the program with an empty csv file and I add one assignment, and then a duplicate assignment, I receive this error message (sorry for the bad formatting, I couldn't figure out how to do it properly):

File "/Users/max/Desktop/Coding/Python/Misc./homeworkPlannerRevised.py", line 212, in checkDuplicates duplicateLabel.grid(row=0, column=0, columnspan=2) File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/tkinter/__init__.py", line 2493, in grid_configure self.tk.call( _tkinter.TclError: bad window path name ".!labelframe.!labelframe.!label6"

Why is this error occurring and how do I fix it? Thanks in advance!

CodePudding user response：

.destroy() removes widget from window (and memory) but it doesn't remove path from variable.
print(duplicateLabel) shows path to object even if it is destroyed.

You run destroy() in loop - so one loop can destroy label and next loop may try to destroy it again - and this can make problem.

You could assign None to variable after destroying and check None before destroying.

if duplicateLabel is not None:
    duplicateLabel.destroy()
    duplicateLabel = None

but if you destroy object then later you have to create it again

if duplicateLabel is None:
   duplicateLabel = Label(...)

But frankly you don't need destroy() but grid_forget() to hide widget without destroying.

if self.course == assignment[1] and self.dueDate == assignment[2] and self.details == assignment[3]:
    duplicateLabel.grid(row=0, column=0, columnspan=2)
else:
    duplicateLabel.grid_forget()