Reflected Operands

reflected-operands.ipynb

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      "name": "Reflected Operands",
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      "source": [
        "<a href=\"https://colab.research.google.com/gist/simecek/8be0adf3d3f1cd0f82524229efeb4216/reflected-operands.ipynb\" target=\"_parent\"><img src=\"https://colab.research.google.com/assets/colab-badge.svg\" alt=\"Open In Colab\"/></a>"
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      "source": [
        "## A custom class for modular arithmetic"
      ]
    },
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      "source": [
        "class Mod(object):\n",
        "  def __init__(self, value, mod):\n",
        "    self.value = value % mod\n",
        "    self.mod = mod\n",
        "  def __repr__(self):\n",
        "    return f'{self.value} (mod {self.mod})'\n",
        "  def __add__(self, i):\n",
        "    new_value = (self.value + i) % self.mod\n",
        "    return Mod(new_value, self.mod)"
      ],
      "execution_count": 0,
      "outputs": []
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        "outputId": "039f6abc-7f5d-48f9-a21e-0b3077f7ffd4"
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      "source": [
        "# this works ok (calls Mod.__add__)\n",
        "Mod(4, mod=7) + 4"
      ],
      "execution_count": 2,
      "outputs": [
        {
          "output_type": "execute_result",
          "data": {
            "text/plain": [
              "1 (mod 7)"
            ]
          },
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            "tags": []
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          "execution_count": 2
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      "source": [
        "# this throws an error because (calls int.__add__)\n",
        "4 + Mod(4, mod=7)"
      ],
      "execution_count": 3,
      "outputs": [
        {
          "output_type": "error",
          "ename": "TypeError",
          "evalue": "ignored",
          "traceback": [
            "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
            "\u001b[0;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
            "\u001b[0;32m<ipython-input-3-24edf17886ea>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0;36m4\u001b[0m \u001b[0;34m+\u001b[0m \u001b[0mMod\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;36m4\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mmod\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0;36m7\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
            "\u001b[0;31mTypeError\u001b[0m: unsupported operand type(s) for +: 'int' and 'Mod'"
          ]
        }
      ]
    },
    {
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      "source": [
        "### Corrected version (with `__radd__` method)"
      ]
    },
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      "source": [
        "class CorrectedMod(object):\n",
        "  def __init__(self, value, mod):\n",
        "    self.value = value % mod\n",
        "    self.mod = mod\n",
        "  def __repr__(self):\n",
        "    return f'{self.value} (mod {self.mod})'\n",
        "  def __add__(self, i):\n",
        "    new_value = (self.value + i) % self.mod\n",
        "    return CorrectedMod(new_value, self.mod)\n",
        "  def __radd__(self, i):\n",
        "    return self.__add__(i)"
      ],
      "execution_count": 0,
      "outputs": []
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        "outputId": "05b3cab6-5bf1-4c74-894f-8a01f39ff70e"
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      "source": [
        "4 + CorrectedMod(4, mod=7)"
      ],
      "execution_count": 5,
      "outputs": [
        {
          "output_type": "execute_result",
          "data": {
            "text/plain": [
              "1 (mod 7)"
            ]
          },
          "metadata": {
            "tags": []
          },
          "execution_count": 5
        }
      ]
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      "source": [
        "Another example on Stack Overflow: \n",
        "\n",
        "https://stackoverflow.com/questions/41598203/overloading-bitwise-operators-to-work-with-booleans-in-python"
      ]
    }
  ]
}