trying to reproduce E.Zag's issue with λ

tkinter_intvar_lambda_issue.ipynb

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   "cell_type": "code",
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   "source": [
    "import tkinter as tk"
   ]
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "See [E.Zag's question on stackoverflow](http://stackoverflow.com/questions/43831296/how-to-assign-unique-intvar-s-to-a-large-set-of-checkbuttons-in-tkinter/43832036#comment74702106_43832036); I'm trying to reproduce their issue.\n",
    "\n",
    "Here's their code, unaltered except for the default argument in the λ to bind to var (`command=lambda v=var: ...`):"
   ]
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   "source": [
    "class application():\n",
    "\n",
    "    def __init__(self):\n",
    "        self.win = tk.Tk()\n",
    "        self.createWidgets()\n",
    "\n",
    "    def createWidgets(self):\n",
    "        a=[]\n",
    "        b=[]\n",
    "        c=[1 for i in range(7)]\n",
    "        k=1\n",
    "        for index, item in enumerate(c):\n",
    "            var=tk.IntVar()\n",
    "            a.append(var)\n",
    "            check=tk.Checkbutton(self.win, text='Button %d' %(k), command=lambda v=var: self.a(v.get()), variable=var)\n",
    "            b.append(check)\n",
    "            b[index].grid(row=k)\n",
    "            k=k+1\n",
    "\n",
    "    def a(self, var):\n",
    "        print(var)"
   ]
  },
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   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
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     "name": "stdout",
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     "text": [
      "1\n",
      "1\n",
      "1\n",
      "1\n",
      "1\n",
      "1\n",
      "1\n"
     ]
    }
   ],
   "source": [
    "if __name__ == \"__main__\":\n",
    "    app = application()\n",
    "    app.win.mainloop()\n",
    "\n",
    "# another window appears.\n",
    "# Clicking the buttons in sequence, then close that window:"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "All these ones are making me suspicious. I want some indication of what happens:"
   ]
  },
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   "execution_count": 4,
   "metadata": {
    "collapsed": true
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   "outputs": [],
   "source": [
    "class verbose_application():\n",
    "\n",
    "    def __init__(self):\n",
    "        self.win = tk.Tk()\n",
    "        self.createWidgets()\n",
    "\n",
    "    def createWidgets(self):\n",
    "        a=[]\n",
    "        b=[]\n",
    "        c=[1 for i in range(7)]\n",
    "        k=1\n",
    "        for index, item in enumerate(c):\n",
    "            var=tk.IntVar()\n",
    "            a.append(var)\n",
    "            check=tk.Checkbutton(self.win, text='Button %d' %(k), command=lambda v=var: self.a(v.get()), variable=var,\n",
    "                                onvalue=k, offvalue=-k)   # <-- this is new\n",
    "            b.append(check)\n",
    "            b[index].grid(row=k)\n",
    "            k=k+1\n",
    "\n",
    "    def a(self, var):\n",
    "        print(var)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1\n",
      "2\n",
      "3\n",
      "4\n",
      "5\n",
      "6\n",
      "7\n",
      "-1\n",
      "-2\n",
      "-3\n",
      "-4\n",
      "-5\n",
      "-6\n",
      "-7\n"
     ]
    }
   ],
   "source": [
    "if __name__ == \"__main__\":\n",
    "    app = verbose_application()\n",
    "    app.win.mainloop()\n",
    "\n",
    "# another window appears.\n",
    "# Clicking the buttons in sequence, and then clicking again to unselect:"
   ]
  }
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