tkinter creating buttons in for loop passing command arguments

Question

I am trying to create buttons in tkinter within a for loop. And with each loop pass the i count value out as an argument in the command value. So when the function is called from the command value I can tell which button was pressed and act accordingly.

The problem is, say the length is 3, it will create 3 buttons with titles Game 1 through Game 3 but when any of the buttons are pressed the printed value is always 2, the last iteration. So it appears the buttons are being made as separate entities, but the i value in the command arguments seem to be all the same. Here is the code:

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) 

Is there a way to get the current i value, each iteration, to stick with that particular button?

Answer 1

Change your lambda to lambda i=i: self.open_this(i).

This may look magical, but here's what's happening. When you use that lambda to define your function, the open_this call doesn't get the value of the variable i at the time you define the function. Instead, it makes a closure, which is sort of like a note to itself saying "I should look for what the value of the variable i is at the time that I am called". Of course, the function is called after the loop is over, so at that time i will always be equal to the last value from the loop.

Using the i=i trick causes your function to store the current value of i at the time your lambda is defined, instead of waiting to look up the value of i later.