On clicking the numbers to input it onto the entry widget, it always adds 10 rather than the number supposed to

Question

for i in range(1,4):
    for j in range(3):
        button = tk.Button(text=str(num+1),master=window,padx=40,pady=20,command=lambda:button_click(num+1))
        button.grid(row=i,column=j)
        num+=1


def button_click(Number):
    ent_number.insert(tk.END,Number)

Whenever I click any button, which shows the appropriate numbers i.e 1,2,3,etc. it always inserts 10 to the entry widget.

You use `num+1` in your code, but you don't define it. Where does it come from, and is `num` maybe equal to 9? — joanis, Apr 08 '22 at 14:52
Does this answer your question? https://stackoverflow.com/questions/71716380/function-not-changing-with-for-loop-python — Sriram Srinivasan, Apr 08 '22 at 15:03
@SriramSrinivasan Yes that does. If it isn't a bother, why does lambda num=num: button_click(num) solve this? Is it because lambda has a property where it will change the value as we go in the for loop? Thanks — Afif Mohammed Varikkodan, Apr 08 '22 at 15:11
@AfifMohammedVarikkodan Was the explanation in the answer clear to you? If you have any doubts, please feel free to ask. — Sriram Srinivasan, Apr 08 '22 at 16:29
@SriramSrinivasan yes it did. Thank you for your explanation, it makes sense now. — Afif Mohammed Varikkodan, Apr 08 '22 at 20:01

score 0 · Accepted Answer · answered Apr 08 '22 at 15:36

You can easily solve your problem by making num a default parameter:

lambda num=num: button_click(num)

Why does this work?

A pre-defined variable in a function could either be a parameter or a global variable. The first preference goes to the function parameter.

For example, if you execute the below code, it will print out 10, not 6.

def func(num):
    print(num)
    
num = 6
func(10)

In your code, when you use lambda:button_click(num+1), num is considered a global variable and the value of num is always 10 irrespective of which button triggered the event.

However, when num is passed as a parameter, the parametric value doesn't change with iterations of the loop. When the function is executed, the parametric value of num is considered, which depends on the source button.

On clicking the numbers to input it onto the entry widget, it always adds 10 rather than the number supposed to

1 Answers1

Why does this work?

Linked