How Can I Pass Unique Arguments to Multiple Tkinter Buttons Created in a Loop?

Understanding Button Creation in Tkinter with Command Arguments

In Tkinter, creating multiple buttons within a loop can be useful for generating dynamic user interfaces. However, passing command arguments to buttons can present challenges, especially when trying to distinguish which button was pressed.

Consider the following code, where buttons are created with their titles incremented by the loop counter:

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

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

The issue arises when we attempt to print the button's identifier (myNum) upon clicking any of them. The output consistently displays 2, the value of the last iteration. This behavior indicates that the buttons are essentially indistinguishable despite their unique titles.

Resolving the Problem

To resolve this issue, we need to ensure that each button captures its own distinct value of i at the time of creation. To achieve this, we can employ a clever technique with lambda functions:

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)

By adding the assignment i=i within the lambda function, we effectively "freeze" the current value of i at the time the lambda is defined. This ensures that each button maintains its unique identifier even after the loop completes.

Conclusion

This technique allows us to create multiple Tkinter buttons dynamically within a loop, where each button can be identified uniquely when clicked. By understanding the behavior of lambda functions and closures, we can achieve more control and flexibility in our Tkinter applications.

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