How to Avoid Parameter Duplication in Tkinter Button Creation Using For Loops?

Overcoming Button Parameter Duplication in Tkinter For Loops

In Tkinter, creating buttons through a for loop can introduce unexpected behavior if proper parameter assignment is not implemented. Consider the following code snippet:

users = {"Test": "127.0.0.0", "Test2": "128.0.0.0"}
row = 1
for name in users:
    user_button = Tkinter.Button(self.root, text=name,
                                 command=lambda: self.a(name))
    user_button.grid(row=row, column=0)
    row += 1

The intended outcome is for each button to receive its own unique parameter from the users dictionary. However, pressing any button results in only the last value from the dictionary (e.g. "Test2") being printed.

This issue arises because lambda expressions use the same name variable throughout the loop. Each iteration overwrites the previous value, leaving the lambda with the last assigned name from the loop.

Solution: Default Keyword Parameters in Lambda

To resolve this, you can employ default keyword parameters in your lambda expression. Here's the corrected code:

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

By explicitly binding the current value of the name variable to the lambda's name keyword argument, the lambda retains the correct parameter for each button. Each button press now triggers the desired unique parameter output.

This technique effectively ensures that each button retains its intended parameter assignment within the for loop.

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