tkinter python - menu button doesnt work with a loop

Question

I have a project with a problem that I recreated in this small code

from tkinter import *
    
top = Tk()
    
mb=  Menubutton ( top, text="condiments", relief=RAISED )
mb.grid()
mb.menu =  Menu ( mb, tearoff = 0 )
mb["menu"] =  mb.menu

for dressing in ['ketchup','mayo']:
    mb.menu.add_command( label=dressing , command=lambda:print(dressing))

mb.pack()
top.mainloop()

so in this example, no matter what I choose in the menu - it prints "mayo" because the last dressing in the loop is mayo and the loop created the menu.

Does anyone have an idea how to fix this issue?

Answer 1

Try this

from tkinter import *

top = Tk()
    
mb=Menubutton(top,text="condiments",relief=RAISED)
mb.grid()
mb.menu=Menu(mb,tearoff=0)
mb["menu"]=mb.menu

for dressing in ['ketchup','mayo']:
    mb.menu.add_command(label=dressing,command=lambda d=dressing:print(d))

mb.pack()
top.mainloop()

Adding d=dressing stores the current value of dressing in a variable d which is sent to the print statement.

it prints "mayo" because the last dressing in the loop is mayo

That's the precise reason, when the lambda function was executed later, it took the last assigned value of dressing which in your case happens to be mayo and not the value that it had at the time of assignment.