Python loop dictionary items through a tkinter GUI using a button

In your callBack method, globalvar = number + 1 does not update the value of the global variable globalvar, it creates a new local variable called globalvar. If you want the globalvar variable to be altered, you have to add global globalvar in your method to explicitly refer to your global variable.

def callBack(number):    global globalvar    globalvar = number + 1    item(globalvar)

Note that using such a global variable, you do not need to have the value passed as a parameter and could just use Button(...,command=callBack)

Other remarks:

• with the grid geometry manager, you do not have to create the 20x14 "empty label" table (removing this loop will not change anything)
• in item method, instead of creating a Label, you could update the text of the existing one (it implies (1) holding a reference to the label in a variable (2) call config(text="new text") on this reference). Creating new labels will reveal hazardous when replacing a label by a shorter (you are now just stacking them on top of others)
• when you initialize B, L, I, V, you do not store anything in the variable. You store the answer of the call to grid (which is always None). To keep a reference on items you have to split your code in two lines :

L = Label(root, text="What comes in the following", fg="blue")L.grid(row=6, column=0)

So, what exactly is the problem? The title mentions looping through a dictionary. Tkinter is no different than any other library - you can do looping like you do for anything else.

For example:

for thing in ("Lettuce", "Cabbage", "Cheese"):    var[thing] = IntVar()    cb[thing] = Checkbutton(root, text=thing, variable=var[thing], ...)    cb[thing].grid(...)

Is there something more you were looking for?