python_defensive_programming.ipynb

python_defensive_programming.ipynb

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        "<a href=\"https://colab.research.google.com/gist/qingfengxia/68b1d29837dd43d8493a38112a428c8e/untitled0.ipynb\" target=\"_parent\"><img src=\"https://colab.research.google.com/assets/colab-badge.svg\" alt=\"Open In Colab\"/></a>"
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      "cell_type": "markdown",
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      "source": [
        "## Defensive programming\n",
        "- make your code safer and more reliable\n",
        "- your model more robust"
      ]
    },
    {
      "cell_type": "code",
      "metadata": {
        "id": "7gSpn94-SpoD",
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      "source": [
        "import math\n",
        "def mySqrt(X):\n",
        "  sum = 0.0\n",
        "  for x in X:\n",
        "    sum = sum + x\n",
        "  return math.sqrt(sum)\n",
        "\n",
        "mySqrt([1, 3])"
      ],
      "execution_count": 0,
      "outputs": []
    },
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "g6RmZoevTY4W",
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      "source": [
        "In this function, the develper has several assumpitons\n",
        "+ the input data is iterable\n",
        "+ the sum is greater or equal to zero\n",
        "\n",
        "but the users of this functions do not know this assumptions\n",
        "\n",
        "NOTE: *do not expect user will read the code before using it*"
      ]
    },
    {
      "cell_type": "code",
      "metadata": {
        "id": "bURn5fgEUHjJ",
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      "source": [
        "mySqrt(10)"
      ],
      "execution_count": 0,
      "outputs": []
    },
    {
      "cell_type": "markdown",
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      "source": [
        "another user's input"
      ]
    },
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      "source": [
        "mySqrt([-5, 1])"
      ],
      "execution_count": 0,
      "outputs": []
    },
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "HFb8k2L4Uxf1",
        "colab_type": "text"
      },
      "source": [
        "+ What does that error mean? \n",
        "+ What is wrong with it? a bug in the function?\n",
        "\n",
        "What the function develope can do for better user experience?"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "ByOo_oYXVLZZ",
        "colab_type": "text"
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      "source": [
        "Does this improved version better?"
      ]
    },
    {
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      "source": [
        "def mySqrt1(X):\n",
        "  # accept an iterable sequence: tuple, list, 1D numpy array of numeric\n",
        "  sum = 0.0\n",
        "  for x in X:\n",
        "    sum = sum + x\n",
        "  return math.sqrt(sum)"
      ],
      "execution_count": 0,
      "outputs": []
    },
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "H1uI2BqMWpnP",
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      },
      "source": [
        "Is there any better approach? Yes\n",
        "\n",
        "Note: good library developers will do their best to prevent misusage!"
      ]
    },
    {
      "cell_type": "code",
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          "height": 36
        },
        "outputId": "8422da0d-f962-46c7-bcba-e2d9c6a3f611"
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      "source": [
        "import math\n",
        "def mySqrt2(X):\n",
        "  # accept an iterable sequence: tuple, list, 1D numpy array of numeric\n",
        "  assert hasattr(X, '__getitem__')  # pre-condition check\n",
        "  sum = 0.0\n",
        "  for x in X:\n",
        "    sum = sum + x\n",
        "  assert sum>=0.0  # post condition check\n",
        "  return math.sqrt(sum)\n",
        "\n",
        "\n",
        "mySqrt2([81])\n",
        "mySqrt2([])  # reasonable good response"
      ],
      "execution_count": 5,
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