for loop to place buttons not working (Python, Tkinter)

Question

I used a for loop to place buttons for a calculator in Tkinter. The idea is simple: every button is placed in a specific row and column, based on its value. This is the code (I wanted to make it generic):

for i in range(10):
    btn = tk.Button(root,
                text=str(i),
                command=lambda: expression.set(expression.get() + str(i)),
                width=10,
                height=2
                )
    row = 3 - (i - 1) // 3
    col = i % 3
    col += 3 if not col else 0
    col = col if i else 2
    btn.grid(row=row, columns=col)
    #print(f"{i}: {row}, {col}") ## Debug
    nums.append(btn)

Here's a screenshow of the result:

I tried to print rows and columns and the output is:

0: 4, 2
1: 3, 1
2: 3, 2
3: 3, 3
4: 2, 1
5: 2, 2
6: 2, 3
7: 1, 1
8: 1, 2
9: 1, 3

Which seems okay, so I guess there's something I don't understand in Tkinter grid.

Not related to your immediate problem but change command=lambda: ... to command=lambda i=i: .... It will save you a few min of debugging. — TheLizzard
– TheLizzard, Commented Jan 9, 2023 at 22:16

Bryan Oakley · Accepted Answer · 2023-01-09 22:38:03Z

1

You have a typo in this line:

btn.grid(row=row, columns=col)

columns (plural) is treated as a shortcut for columnspan. Since you don't specify the column with column (singular), all buttons are going in column zero with a columnspan equal to whatever is in col.

TL;DR: change columns=col to column=col.

edited Jan 9, 2023 at 22:38

answered Jan 9, 2023 at 22:15

Bryan Oakley

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6 Comments

TheLizzard Over a year ago

Do you know why that shortcut exists? columns doesn't appear to be in the tcl docs. In the docs it's specified as columnspan. I know about the bd/border shortcut but sometimes bd stands for something else - I think. I don't see the point to those shortcuts.

Bryan Oakley Over a year ago

@TheLizzard: the shortcut exists because the underlying tcl/tk interpreter supports abbreviating all options to the shortest unique string possible. You can find a mention of it in the options man page: "Command-line switches may be abbreviated, as long as the abbreviation is unambiguous. " In that context, "command-line switches" refers to options of a tk command (eg: -background, -command, etc). I don't see it mentioned anywhere in the official tkinter documentation.

TheLizzard Over a year ago

Didn't know that was part of tcl but column and columns are too close imo. I am surprised that I haven't made this typo before. colspan and rowspan seem more logical abbreviations. Also tkinter's official docs aren't well designed and are missing quite a bit of info.

Bryan Oakley Over a year ago

@TheLizzard: I agree, the tkinter docs are a bit shallow. I suspect that when they first wrote them, they assumed the reader was already very familiar with tcl/tk. Also, this isn't a tcl feature, it's specific to how tk handles command options.

TheLizzard Over a year ago

Welp, I will have to read more about tk vs tcl and how they handle arguments. Thx for the info.

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