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Add playground.ipynb
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‎README.md

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raise ModuleNotFoundError
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```
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## Experiments
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See [playground.ipynb](./playground.ipynb) for some experiments on the diagram.
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[1]: https://docs.python.org/3/reference/import.html
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‎playground.ipynb

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{
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"metadata": {
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.7.8-final"
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},
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"orig_nbformat": 2,
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"kernelspec": {
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"name": "python3",
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"display_name": "Python 3",
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"language": "python"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 2,
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"cells": [
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{
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"source": [
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"### `None` in sys.modules"
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],
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"cell_type": "markdown",
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"metadata": {}
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"metadata": {},
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"outputs": [
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{
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"output_type": "error",
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"ename": "ModuleNotFoundError",
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"evalue": "import of module halted; None in sys.modules",
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"traceback": [
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"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
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"\u001b[0;31mModuleNotFoundError\u001b[0m Traceback (most recent call last)",
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"\u001b[0;32m<ipython-input-1-20156aa94da0>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m 2\u001b[0m \u001b[0msys\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mmodules\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;34m'module'\u001b[0m\u001b[0;34m]\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;32mNone\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 3\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 4\u001b[0;31m \u001b[0;32mimport\u001b[0m \u001b[0mmodule\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
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"\u001b[0;31mModuleNotFoundError\u001b[0m: import of module halted; None in sys.modules"
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]
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}
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],
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"source": [
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"import sys\n",
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"sys.modules['module'] = None\n",
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"\n",
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"import module"
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]
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},
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{
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"source": [
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"### `sys.meta_path` exhausted"
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],
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"cell_type": "markdown",
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"metadata": {}
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},
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{
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"source": [
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"del sys.modules['module']\n",
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"del sys.meta_path[:]\n",
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"\n",
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"import module"
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],
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"cell_type": "code",
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"metadata": {},
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"execution_count": 2,
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"outputs": [
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{
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"output_type": "error",
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"ename": "ModuleNotFoundError",
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"evalue": "No module named 'module'",
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"traceback": [
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"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
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"\u001b[0;31mModuleNotFoundError\u001b[0m Traceback (most recent call last)",
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"\u001b[0;32m<ipython-input-2-fd1bf8284402>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m 2\u001b[0m \u001b[0;32mdel\u001b[0m \u001b[0msys\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mmeta_path\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 3\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 4\u001b[0;31m \u001b[0;32mimport\u001b[0m \u001b[0mmodule\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
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"\u001b[0;31mModuleNotFoundError\u001b[0m: No module named 'module'"
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]
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}
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]
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},
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{
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"source": [
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"### Spec's loader is `None`"
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],
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"cell_type": "markdown",
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"metadata": {}
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},
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{
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"cell_type": "code",
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"execution_count": 7,
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"metadata": {},
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"outputs": [
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{
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"output_type": "error",
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"ename": "ImportError",
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"evalue": "missing loader",
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"traceback": [
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"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
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"\u001b[0;31mImportError\u001b[0m Traceback (most recent call last)",
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"\u001b[0;32m<ipython-input-7-85f7fa80cfc0>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m 9\u001b[0m \u001b[0msys\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mmeta_path\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m[\u001b[0m\u001b[0mfinder\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 10\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 11\u001b[0;31m \u001b[0;32mimport\u001b[0m \u001b[0mmodule\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
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"\u001b[0;31mImportError\u001b[0m: missing loader"
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]
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}
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],
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"source": [
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"from importlib.abc import MetaPathFinder\n",
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"from importlib.machinery import ModuleSpec\n",
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"\n",
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"class NoLoaderFinder(MetaPathFinder):\n",
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" def find_spec(self, fullname, path, target=None):\n",
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" return ModuleSpec('module', None)\n",
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"\n",
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"finder = NoLoaderFinder()\n",
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"sys.meta_path = [finder]\n",
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"\n",
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"import module"
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]
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},
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{
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"source": [
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"### Regular loader"
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],
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"cell_type": "markdown",
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"metadata": {}
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},
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{
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"cell_type": "code",
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"execution_count": 17,
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"metadata": {},
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"outputs": [
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{
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"output_type": "stream",
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"name": "stdout",
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"text": [
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"module <module 'module' (<__main__.ExampleLoader object at 0x7f782ed6e3d0>)>\nmodule.name module\nmodule.x 1\nmodule.y 2\n----------\nmodule2 is module? False\nmodule2 <module 'module' (<__main__.ExampleLoader object at 0x7f782deab5d0>)>\nmodule2.name module\nmodule2.x 1\nmodule2.y 2\n"
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]
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}
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],
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"source": [
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"from types import ModuleType\n",
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"from importlib.abc import Loader\n",
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"\n",
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"class Module(ModuleType):\n",
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" def __init__(self, name):\n",
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" self.x = 1\n",
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" self.name = name\n",
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"\n",
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"class ExampleLoader(Loader):\n",
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" def create_module(self, spec):\n",
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" return Module(spec.name)\n",
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"\n",
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" def exec_module(self, module):\n",
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" module.y = 2\n",
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"\n",
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"class ExampleFinder(MetaPathFinder):\n",
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" def find_spec(self, fullname, path, target=None):\n",
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" return ModuleSpec('module', ExampleLoader())\n",
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"\n",
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"sys.meta_path = [ExampleFinder()]\n",
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"\n",
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"import module\n",
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"print('module', module)\n",
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"print('module.name', module.name)\n",
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"print('module.x', module.x)\n",
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"print('module.y', module.y)\n",
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"\n",
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"del sys.modules['module']\n",
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"\n",
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"print('-' * 10)\n",
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"module2 = __import__('module')\n",
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"\n",
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"print('module2 is module?', module2 is module)\n",
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"print('module2', module2)\n",
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"print('module2.name', module2.name)\n",
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"print('module2.x', module2.x)\n",
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"print('module2.y', module2.y)\n",
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"\n"
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]
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}
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]
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}

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