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    {
      "cell_type": "markdown",
      "id": "3e81438d-dc33-4fc9-a304-47851da7a752",
      "metadata": {},
      "source": [
        "# PYTHONPATH Tricks"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "4a51f064-0bb2-4c9b-bddd-49a94e3c7230",
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      "source": [
        "### What is PYTHONPATH\n",
        "PYTHONPATH is an environment variable that defines where python looks for importable modules\n",
        "\n",
        "In bash, running `echo $PYTHONPATH` will show you the current path\n",
        "\n",
        "Python then adds the directories in that path to `sys.path` at runtime"
      ]
    },
    {
      "attachments": {},
      "cell_type": "markdown",
      "id": "f20393d5-bbb2-472b-9549-4c8b8ec1b7b5",
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      "source": [
        "### Handling of dependencies with multiple versions\n",
        "\n",
        "If there are multiple versions of a package in `sys.path`, python searches `sys.path` in order and uses the first one found\n",
        "\n",
        "#### Experiment\n",
        "To prove this, setup the following scenario\n",
        "\n",
        "File: ~/package1/package.py\n",
        "def version():\n",
        "    return \"Version 1\"\n",
        "\n",
        "File: ~/package2/package.py\n",
        "def version():\n",
        "    return \"Version 2\"\n",
        "\n",
        "bash: `PYTHONPATH=~/package1/package.py:~/package2/package.py python`\n",
        "Inside the python interpreter: `import package; package.version()`\n",
        "Output: Version 1\n",
        "\n",
        "This makes sense, running `import sys; sys.path` shows us that package1 is listed first hence it was loaded"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "ebf61e77-2071-4787-b71c-09439a2d7794",
      "metadata": {},
      "source": [
        "## Overriding default resolution behaviors"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "id": "e1b84fc0-236f-4b5d-8b8d-7cf11b403951",
      "metadata": {
        "trusted": true
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      "source": [
        "### Changing default behavior, using path above, package.version() will output Version 1\n",
        "import os\n",
        "import sys\n",
        "MODULE = 'package'\n",
        "\n",
        "def printPackageVersion():\n",
        "    pass",
        "    #import package\n",
        "    #print(f\"Currently loaded package version {package.version()}\")\n",
        "\n",
        "if 'package' in sys.modules.keys():\n",
        "    # If already imported from somewhere else, remove\n",
        "    printPackageVersion()\n",
        "    del sys.modules[MODULE]\n",
        "\n",
        "# Changing to Version 2 of our package\n",
        "# sys.path was [\"\", \"package1\" \"package2\"] but will be [\"\", \"package2\", \"package1\"] now\n",
        "sys.path.insert(1, os.path.abspath(\"~/package2\"))\n",
        "printPackageVersion() # outputs Version2 \n",
        "\n",
        "# What if we wanted to use both versions of the package and use them both in the same file\n",
        "import importlib.util\n",
        "spec = importlib.util.spec_from_file_location('package', '~/package1/package.py')\n",
        "mod = importlib.util.module_from_spec(spec)\n",
        "#spec.loader.exec_module(mod)\n",
        "\n",
        "#mod.version() # Outputs Version 1\n",
        "#package.version() # Outputs Version 2\n",
        "\n",
        "# What about overriding the already loaded version of the module with our new version\n",
        "# Now our module versions are out of sync, to hack in Version 1 again globally\n",
        "#del sys.modules[MODULE]\n",
        "#sys.modules[MODULE] = mod\n",
        "\n",
        "#mod.version() # Outputs Version 1\n",
        "#package.version() # Outputs Version 1"
      ]
    }
  ],
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    "kernelspec": {
      "display_name": "Python (Pyodide)",
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