How to Avoid Variable Scope Issues When Assigning Tkinter Button Commands in a Loop?

Tkinter Button Command Assignment in a For Loop Using Lambda

In Tkinter, a common task is to create a series of buttons using a for loop. However, when assigning commands to these buttons with a lambda function, a pitfall arises.

The issue occurs when using a variable name within the lambda function that is also used in the for loop iterator. This variable is constantly reassigned as the loop progresses, leading to all buttons using the same value for the assigned variable.

To resolve this, modify the lambda expression by introducing a default keyword argument. This binds the current value of the variable to the lambda's keyword argument each time through the loop:

user_button = Tkinter.Button(self.root, text=name,
                             command=lambda name=name: self.a(name))

By assigning the variable name to the name keyword argument, the current value is bound to the argument each iteration. This ensures that each button retains its unique parameter when clicked.

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