How to Pass Unique Arguments to Commands in Tkinter Button Loops?

Programmatically Creating Buttons in tkinter with Unique Command Arguments

The task at hand is to generate several buttons within a tkinter interface using a for loop. Each button should contain a unique command argument representing the current iteration count. However, the existing code yields buttons with consistent printed values, indicating a potential issue with the command argument assignment.

The Issue: Disappearing Iteration Values

The provided code creates buttons with titles ranging from "Game 1" to "Game 3." Upon clicking any of these buttons, the printed value is always 2, corresponding to the last iteration count. This suggests that the command arguments are being treated as a single entity, rather than being associated with each individual button.

The Solution: Preserving Iteration Values

The key to resolving this issue lies in preserving the current iteration value (i) when defining the command for each button. To achieve this, a modified lambda expression is required:

command=lambda i=i: self.open_this(i)

This lambda expression assigns the current value of i to a variable named i. This ensures that the i value is captured and attached to the specific button at the time of creation. As a result, each button will have access to its unique iteration count.

Understanding Lambda Closures

By using i=i, the closure stores the current value of i at the time the lambda is defined, rather than relying on the value of i at the time the function is called. This preserves the necessary information for each button.

Fixed Code

With the aforementioned modification, the corrected code appears as follows:

def createGameURLs(self):
    self.button = []
    for i in range(3):
        self.button.append(Button(self, text='Game '+str(i+1),
                                  command=lambda i=i: self.open_this(i)))
        self.button[i].grid(column=4, row=i+1, sticky=W)

def open_this(self, myNum):
    print(myNum)

Now, upon clicking any of the buttons, the corresponding iteration count will be printed accurately, resolving the initial issue.

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