Bind Tkinter Grid Button Callbacks to Row and Column: Using Lambda Default Arguments (and functools.partial)

Fix Tkinter grid callbacks by capturing row and column with lambda defaults. Learn why loop closures fail and see examples with functools.partial in Python.

When you generate a grid of tk.Button widgets in nested loops, all of them can end up calling the same callback without any hint about which cell was pressed. For a minesweeper board, that makes it impossible to tell whether the user clicked (2, 3) or (7, 8). The fix is straightforward once you understand how Python binds variables in callbacks.

Problem setup

Below is a minimalized fragment that builds a 10×10 board on a Canvas and assigns one shared handler to every button. It shows the essence of the issue: the callback receives no coordinates, so you can’t identify the clicked cell.

import tkinter as tk

# simplified handler used by all buttons

def on_cell():
    pass

pos_x = -400
pos_y = -200
cell_idx = 0
btn_cells = []

# imagine this canvas comes from turtle's screen.getcanvas()
root = tk.Tk()
cnv = tk.Canvas(root)
cnv.pack()

for r in range(10):
    for c in range(10):
        btn_cells.append([tk.Button(cnv.master, text="////", command=on_cell)])
        cnv.create_window(pos_x, pos_y, window=btn_cells[cell_idx])
        cell_idx += 1
        pos_x += 40
    pos_y += 40
    pos_x += -400

root.mainloop()

Every widget points at the same function that takes no arguments, so at click time there is no row or column to work with. Trying to rely on mouse coordinates is fragile for a grid snapped to a logical board.

What actually goes wrong

Reusing a single function is fine, but the function needs stable, per-button data about its position. If you try to close over loop variables directly, Python will resolve them when the callback runs, not when it’s created. After the loops finish, those variables typically hold their last values, and all buttons report the same coordinates. The reliable way is to bind the current row and column at definition time using default arguments.

The fix: capture indices via default arguments

Pass a lambda to command that freezes the current loop indices as default arguments and forwards them to a function that expects row and column. This keeps the code compact and lets every button report its own coordinates.

#!/usr/bin/python3
import tkinter as tk


def cell_hit(rx, cx):
    print("Hello from ({}, {})!".format(rx, cx))

app = tk.Tk()
for r in range(10):
    for c in range(10):
        tk.Button(text="{}, {}".format(r, c),
                  command=lambda rr=r, cc=c: cell_hit(rr, cc))\
                  .grid(column=r, row=c)

app.mainloop()

The key detail is command=lambda rr=r, cc=c: cell_hit(rr, cc). The rr and cc defaults capture the current r and c values as constants for that specific button. When the user clicks, those saved values are passed to cell_hit, and you immediately know which cell fired.

Applying the same idea to a Canvas-based layout

If you are placing the buttons inside a Canvas, you can keep the layout logic and only adjust the command to capture indices. The approach is identical: bind per-button data at definition time.

import tkinter as tk


def cell_open(rx, cx):
    print("Clicked cell ({}, {})".format(rx, cx))

x0 = -400
y0 = -200
k = 0
widgets = []

root = tk.Tk()
cv = tk.Canvas(root)
cv.pack()

for r in range(10):
    for c in range(10):
        btn = tk.Button(cv.master, text="////", command=lambda rr=r, cc=c: cell_open(rr, cc))
        widgets.append([btn])
        cv.create_window(x0, y0, window=widgets[k])
        k += 1
        x0 += 40
    y0 += 40
    x0 += -400

root.mainloop()

This preserves the original structure while giving each Button a stable reference to its own row and column.

Why this matters

GUI callbacks are created in loops all the time, not just in simple games. Understanding that Python evaluates free variables when a function is called, and that default arguments snapshot values at definition time, prevents elusive bugs where every widget behaves as if it were the last one created. The same technique keeps your code clean because you don’t need to thread coordinates through global state or reverse-engineer positions from pointer events.

If you prefer a different syntax, you can achieve the same effect with functools.partial, which also binds arguments ahead of time. The core idea remains identical: create a per-button closure over the indices you need.

Takeaways

Make your callbacks self-sufficient. When generating buttons in a loop, freeze the loop variables right in the command. Default arguments in a lambda are a concise and reliable way to do this, and they scale well as the board grows or the callback logic evolves. With that one change, every click carries its own context, and the rest of your minesweeper logic can focus on gameplay instead of guessing which cell was pressed.