Number Of instances.ipynb

number-of-instances.ipynb

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      "name": "Number Of instances.ipynb",
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      "include_colab_link": true
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    "kernelspec": {
      "name": "python3",
      "display_name": "Python 3"
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  "cells": [
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "view-in-github",
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        "<a href=\"https://colab.research.google.com/gist/simecek/b00f0df694c6318130cfeaf1586dca3f/number-of-instances.ipynb\" target=\"_parent\"><img src=\"https://colab.research.google.com/assets/colab-badge.svg\" alt=\"Open In Colab\"/></a>"
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        "outputId": "1c7b3bdb-4eec-4a19-ef54-17f92f7a4b9f"
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      "source": [
        "# This counter does not work\n",
        "\n",
        "class Foo:\n",
        "  _num_instances = 0\n",
        "  def __init__(self):\n",
        "    self._num_instances += 1\n",
        "        \n",
        "f1 = Foo()\n",
        "f2 = Foo()\n",
        "print(Foo._num_instances)"
      ],
      "execution_count": 1,
      "outputs": [
        {
          "output_type": "stream",
          "text": [
            "0\n"
          ],
          "name": "stdout"
        }
      ]
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          "height": 35
        },
        "outputId": "53f47d3b-1b6a-4644-cf04-fd27e93216ad"
      },
      "source": [
        "# This counter works thanks to @classmethod\n",
        "\n",
        "class Foo: \n",
        "  _num_instances = 0\n",
        "  @classmethod\n",
        "  def create(cls):\n",
        "      instance = cls()\n",
        "      cls._num_instances += 1\n",
        "      return instance\n",
        "  \n",
        "f1 = Foo.create()\n",
        "f2 = Foo.create()\n",
        "print(Foo._num_instances)"
      ],
      "execution_count": 2,
      "outputs": [
        {
          "output_type": "stream",
          "text": [
            "2\n"
          ],
          "name": "stdout"
        }
      ]
    },
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        "id": "Fxwao0RC902L",
        "colab_type": "code",
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      "source": [
        ""
      ],
      "execution_count": 0,
      "outputs": []
    }
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