Why Does My Button\'s Command Always Print the Same Index in a Loop with a Lambda?

Understanding Closure in a Lambda: Resolving Variables

In this situation, you're attempting to create multiple buttons within a loop, with each button triggering a command that prints a specific index value. However, you're encountering an issue where the button's command always prints the same index, "5."

This behavior stems from the nature of closures in lambdas. When a lambda is defined, it captures the variables of the enclosing scope and references them when executed. In your case, the enclosing scope is the loop, where the variable i represents the current index.

Unfortunately, when the lambda is executed (when the button is pressed), the value of i has already reached the last iteration and is equal to "5" for all buttons. This is because the captured variable i is a reference to the same memory location, and the value it holds is updated as the loop progresses.

To resolve this issue, you need to create a closure that captures the correct value of i for each button. You can do this by providing a default value for the i parameter in the lambda function. For example:

<code class="python">make_button = Tkinter.Button(frame, text="make!",
                              command=lambda i=i: makeId(i))</code>

By providing i=i as the default value for the lambda parameter, you're creating a local variable i that holds the correct index value for each button. When the button is pressed, the lambda function will execute with the captured local variable i, and the correct index will be printed.

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