{ "cells": [ { "metadata": {}, "cell_type": "markdown", "source": [ "# Seminar 3\n", "\n", "Working with the environment, CLI and Paths\n", "\n", "Exceptions\n", "\n", "Context Managers\n" ], "id": "2d5ff35bc89a985b" }, { "metadata": {}, "cell_type": "markdown", "source": "## Environment", "id": "329669d100c74f24" }, { "metadata": {}, "cell_type": "markdown", "source": [ "Environment variables are often used in applications for configuration.\n", "They can be accessed through os.environ" ], "id": "7c569146099e5cb8" }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T17:39:38.300280600Z", "start_time": "2026-09-22T17:39:38.230260200Z" } }, "cell_type": "code", "source": [ "import os\n", "from zipfile import __main__\n", "\n", "dict(os.environ).keys()" ], "id": "d93366fcc9360f1b", "outputs": [ { "data": { "text/plain": [ "dict_keys(['ALLUSERSPROFILE', 'APPDATA', 'COMMONPROGRAMFILES', 'COMMONPROGRAMFILES(X86)', 'COMMONPROGRAMW6432', 'COMPUTERNAME', 'COMSPEC', 'DRIVERDATA', 'EFC_25080_1262719628', 'EFC_25080_1592913036', 'EFC_25080_2283032206', 'EFC_25080_2775293581', 'EFC_25080_3789132940', 'EFC_25080_4126798990', 'FPS_BROWSER_APP_PROFILE_STRING', 'FPS_BROWSER_USER_PROFILE_STRING', 'HOMEDRIVE', 'HOMEPATH', 'LOCALAPPDATA', 'LOGONSERVER', 'NUMBER_OF_PROCESSORS', 'ONEDRIVE', 'OS', 'PATH', 'PATHEXT', 'PROCESSOR_ARCHITECTURE', 'PROCESSOR_IDENTIFIER', 'PROCESSOR_LEVEL', 'PROCESSOR_REVISION', 'PROGRAMDATA', 'PROGRAMFILES', 'PROGRAMFILES(X86)', 'PROGRAMW6432', 'PROMPT', 'PSMODULEPATH', 'PUBLIC', 'PYDEVD_IPYTHON_COMPATIBLE_DEBUGGING', 'PYTHONDONTWRITEBYTECODE', 'PYTHONIOENCODING', 'PYTHONPATH', 'PYTHONUNBUFFERED', 'SESSIONNAME', 'SYSTEMDRIVE', 'SYSTEMROOT', 'TEMP', 'TMP', 'USERDOMAIN', 'USERDOMAIN_ROAMINGPROFILE', 'USERNAME', 'USERPROFILE', 'VIRTUAL_ENV', 'WINDIR', '_OLD_VIRTUAL_PATH', '_OLD_VIRTUAL_PROMPT', 'PYDEVD_USE_FRAME_EVAL', 'TERM', 'CLICOLOR', 'FORCE_COLOR', 'CLICOLOR_FORCE', 'PAGER', 'GIT_PAGER', 'MPLBACKEND'])" ] }, "execution_count": 2, "metadata": {}, "output_type": "execute_result" } ], "execution_count": 2 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T17:39:40.269582500Z", "start_time": "2026-09-22T17:39:40.192244100Z" } }, "cell_type": "code", "source": [ "# Some of the most common environment variables (in linux)\n", "print('PATH:', os.environ['PATH']) # all executables accessible from anywhere\n", "print('PYTHONPATH:', os.environ['PYTHONPATH']) # python source path\n", "print('PWD:', os.environ['PWD']) # present working directory\n", "print('HOME:', os.environ['HOME']) # home directory\n", "print('USER:', os.environ['USER']) # user\n", "print('Non existing: ', os.environ['NON_EXISTING']) # non existing key" ], "id": "195588e41a0ca403", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "PATH: C:\\Users\\Carlos.Alfonsobasab\\Work\\Python_TA\\seminars\\sem_03\\.venv\\Scripts;C:\\WINDOWS\\system32;C:\\WINDOWS;C:\\WINDOWS\\System32\\Wbem;C:\\WINDOWS\\System32\\WindowsPowerShell\\v1.0\\;C:\\WINDOWS\\System32\\OpenSSH\\;C:\\Program Files\\Git\\cmd;C:\\Program Files\\Cloudflare\\Cloudflare WARP\\;C:\\Program Files\\GitHub CLI\\;C:\\Program Files\\nodejs\\;C:\\Users\\Carlos.Alfonsobasab\\.elan\\bin;C:\\Users\\Carlos.Alfonsobasab\\AppData\\Local\\Programs\\Python\\Python312\\Scripts\\;C:\\Users\\Carlos.Alfonsobasab\\AppData\\Local\\Programs\\Python\\Python312\\;C:\\Users\\Carlos.Alfonsobasab\\AppData\\Local\\Programs\\Python\\Launcher\\;C:\\Users\\Carlos.Alfonsobasab\\AppData\\Local\\Microsoft\\WindowsApps;C:\\Users\\Carlos.Alfonsobasab\\AppData\\Local\\JetBrains\\Toolbox\\scripts;;C:\\Users\\Carlos.Alfonsobasab\\AppData\\Local\\Programs\\DockerDesktop\\resources\\bin;C:\\Users\\Carlos.Alfonsobasab\\.local\\bin;C:\\Users\\Carlos.Alfonsobasab\\AppData\\Local\\Microsoft\\WinGet\\Packages\\AgileBits.1Password.CLI_Microsoft.Winget.Source_8wekyb3d8bbwe\\.;;C:\\Users\\Carlos.Alfonsobasab\\.bun\\bin;C:\\Users\\Carlos.Alfonsobasab\\AppData\\Local\\Microsoft\\WinGet\\Packages\\astral-sh.uv_Microsoft.Winget.Source_8wekyb3d8bbwe;C:\\Users\\Carlos.Alfonsobasab\\AppData\\Local\\Microsoft\\WinGet\\Packages\\Ninja-build.Ninja_Microsoft.Winget.Source_8wekyb3d8bbwe;C:\\Users\\Carlos.Alfonsobasab\\AppData\\Local\\Microsoft\\WinGet\\Packages\\Kitware.CMake_Microsoft.Winget.Source_8wekyb3d8bbwe\\cmake-4.4.2-windows-x86_64\\bin;C:\\Users\\Carlos.Alfonsobasab\\.dotnet\\tools;C:\\Users\\Carlos.Alfonsobasab\\AppData\\Roaming\\npm;C:\\Users\\Carlos.Alfonsobasab\\AppData\\Local\\Programs\\Microsoft VS Code\\bin;C:\\Users\\Carlos.Alfonsobasab\\AppData\\Local\\Microsoft\\WinGet\\Packages\\JetBrains.TeamCityCLI_Microsoft.Winget.Source_8wekyb3d8bbwe;\n", "PYTHONPATH: C:\\Users\\Carlos.Alfonsobasab\\Work\\Python_TA\\seminars\\sem_03;C:/Users/Carlos.Alfonsobasab/AppData/Local/Programs/PyCharm/plugins/python-ce/helpers\n" ] }, { "ename": "KeyError", "evalue": "'PWD'", "output_type": "error", "traceback": [ "\u001B[31m---------------------------------------------------------------------------\u001B[39m", "\u001B[31mKeyError\u001B[39m Traceback (most recent call last)", "\u001B[36mCell\u001B[39m\u001B[36m \u001B[39m\u001B[32mIn[3]\u001B[39m\u001B[32m, line 4\u001B[39m\n\u001B[32m 1\u001B[39m \u001B[38;5;66;03m# Some of the most common environment variables (in linux)\u001B[39;00m\n\u001B[32m 2\u001B[39m print(\u001B[33m'PATH:'\u001B[39m, os.environ[\u001B[33m'PATH'\u001B[39m]) \u001B[38;5;66;03m# all executables accessible from anywhere\u001B[39;00m\n\u001B[32m 3\u001B[39m print(\u001B[33m'PYTHONPATH:'\u001B[39m, os.environ[\u001B[33m'PYTHONPATH'\u001B[39m]) \u001B[38;5;66;03m# python source path\u001B[39;00m\n\u001B[32m----> \u001B[39m\u001B[32m4\u001B[39m print(\u001B[33m'PWD:'\u001B[39m, os.environ[\u001B[33m'PWD'\u001B[39m]) \u001B[38;5;66;03m# present working directory\u001B[39;00m\n\u001B[32m 5\u001B[39m print(\u001B[33m'HOME:'\u001B[39m, os.environ[\u001B[33m'HOME'\u001B[39m]) \u001B[38;5;66;03m# home directory\u001B[39;00m\n\u001B[32m 6\u001B[39m print(\u001B[33m'USER:'\u001B[39m, os.environ[\u001B[33m'USER'\u001B[39m]) \u001B[38;5;66;03m# user\u001B[39;00m\n\u001B[32m 7\u001B[39m print(\u001B[33m'Non existing: '\u001B[39m, os.environ[\u001B[33m'NON_EXISTING'\u001B[39m]) \u001B[38;5;66;03m# non existing key\u001B[39;00m\n", "\u001B[36mFile \u001B[39m\u001B[32m:709\u001B[39m, in \u001B[36m_Environ.__getitem__\u001B[39m\u001B[34m(self, key)\u001B[39m\n", "\u001B[31mKeyError\u001B[39m: 'PWD'" ] } ], "execution_count": 3 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T17:39:44.177321Z", "start_time": "2026-09-22T17:39:44.159076400Z" } }, "cell_type": "code", "source": [ "# bad example\n", "try:\n", " os.environ['NON_EXISTING']\n", "except KeyError:\n", " ...\n", "\n", "# good example\n", "value = os.environ.get('NON_EXISTING', None)\n", "if value is None:\n", " ..." ], "id": "930a99cfc61dbb17", "outputs": [], "execution_count": 4 }, { "metadata": {}, "cell_type": "markdown", "source": "Let's try passing environment variable DATASET_URL to a python script and look at different ways to do it.", "id": "9fd6b8adf0bc8dba" }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T17:39:46.288139600Z", "start_time": "2026-09-22T17:39:46.222725300Z" } }, "cell_type": "code", "source": [ "%%writefile connect_dataset.py\n", "import os\n", "\n", "\n", "def main():\n", " dataset_url = os.environ.get('DATASET_URL', None)\n", " print('DATASET_URL: ', dataset_url)\n", "\n", "if __name__ == '__main__':\n", " main()" ], "id": "6d07093548147787", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Writing connect_dataset.py\n" ] } ], "execution_count": 5 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T17:39:48.354790100Z", "start_time": "2026-09-22T17:39:48.219275700Z" } }, "cell_type": "code", "source": "!python connect_dataset.py", "id": "61b424efe9d6bdd4", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "DATASET_URL: None\n" ] } ], "execution_count": 6 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T17:40:02.917918900Z", "start_time": "2026-09-22T17:40:02.794701400Z" } }, "cell_type": "code", "source": [ "# from terminal:\n", "# DATASET_URL= python connect_dataset.py\n", "\n", "# from jupyter notebook:\n", "import os\n", "os.environ['DATASET_URL'] = \"\"\n", "!python connect_dataset.py" ], "id": "e86872530552ab62", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "DATASET_URL: \n" ] } ], "execution_count": 7 }, { "metadata": {}, "cell_type": "markdown", "source": [ "The standard way to store environment variables is in \".env\" files (which are always put in .gitignore for security).\n", "Dotenv package allows working with such files easily" ], "id": "20d5ed712de6807d" }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T17:40:13.509359500Z", "start_time": "2026-09-22T17:40:12.153511Z" } }, "cell_type": "code", "source": [ "%%capture\n", "!pip install python-dotenv" ], "id": "9309cca7ddb39f3a", "outputs": [], "execution_count": 8 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T17:40:19.437952500Z", "start_time": "2026-09-22T17:40:19.382183700Z" } }, "cell_type": "code", "source": [ "%%writefile .env\n", "DATASET_URL=somenewdataseturl" ], "id": "984d18cc29ad4ed8", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Writing .env\n" ] } ], "execution_count": 9 }, { "metadata": { "ExecuteTime": { "end_time": "2025-08-10T09:16:13.601219Z", "start_time": "2025-08-10T09:16:13.598237Z" } }, "cell_type": "code", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Overwriting env_check.py\n" ] } ], "execution_count": 46, "source": [ "%%writefile env_check.py\n", "from dotenv import load_dotenv\n", "import os\n", "\n", "print('DATASET_URL:', os.environ.get('DATASET_URL'))\n", "load_dotenv('.env')\n", "print('DATASET_URL:', os.environ.get('DATASET_URL'))" ], "id": "fe6c9c60dc68abf0" }, { "metadata": { "ExecuteTime": { "end_time": "2025-08-10T09:16:15.068066Z", "start_time": "2025-08-10T09:16:14.922553Z" } }, "cell_type": "code", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "DATASET_URL: \r\n", "DATASET_URL: \r\n" ] } ], "execution_count": 47, "source": "!python env_check.py", "id": "c7e060332142b724" }, { "metadata": {}, "cell_type": "markdown", "source": "Oops: when env variable is already declared, it is not overwritten by dotenv. Let's delete the old one first.", "id": "562a4af8673ea59b" }, { "metadata": { "ExecuteTime": { "end_time": "2025-08-10T09:16:53.963398Z", "start_time": "2025-08-10T09:16:53.961014Z" } }, "cell_type": "code", "outputs": [], "execution_count": 48, "source": "del os.environ['DATASET_URL']", "id": "896d41c8ed343521" }, { "metadata": { "ExecuteTime": { "end_time": "2025-08-10T09:16:58.643632Z", "start_time": "2025-08-10T09:16:58.498080Z" } }, "cell_type": "code", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "DATASET_URL: None\r\n", "DATASET_URL: somenewdataseturl\r\n" ] } ], "execution_count": 49, "source": "!python env_check.py", "id": "459542fc7dab0fa3" }, { "metadata": {}, "cell_type": "markdown", "source": "### Other ways to load configuration", "id": "a901587d0ad07996" }, { "metadata": {}, "cell_type": "markdown", "source": "#### Yaml", "id": "47f3f158d8b3b5b0" }, { "metadata": { "ExecuteTime": { "end_time": "2025-08-10T09:20:23.170759Z", "start_time": "2025-08-10T09:20:23.167717Z" } }, "cell_type": "code", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Writing config.yaml\n" ] } ], "execution_count": 52, "source": [ "%%writefile config.yaml\n", "database:\n", " url: \"postgresql://user:pass@localhost:5432/db\"\n", " timeout: 30\n", "logging:\n", " level: \"DEBUG\"" ], "id": "4fa4cae6e28a122b" }, { "metadata": { "ExecuteTime": { "end_time": "2025-08-10T11:06:01.100950Z", "start_time": "2025-08-10T11:05:58.971604Z" } }, "cell_type": "code", "outputs": [], "execution_count": 105, "source": [ "%%capture\n", "!pip install pyyaml" ], "id": "70175b3a3b85f058" }, { "metadata": { "ExecuteTime": { "end_time": "2025-08-10T09:20:34.097841Z", "start_time": "2025-08-10T09:20:34.094596Z" } }, "cell_type": "code", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "{'database': {'url': 'postgresql://user:pass@localhost:5432/db', 'timeout': 30}, 'logging': {'level': 'DEBUG'}}\n", "postgresql://user:pass@localhost:5432/db\n" ] } ], "execution_count": 54, "source": [ "import yaml\n", "\n", "with open(\"config.yaml\", 'r') as f:\n", " config = yaml.safe_load(f)\n", "\n", "print(config)\n", "print(config['database']['url'])" ], "id": "5b6f65d959626a74" }, { "metadata": {}, "cell_type": "markdown", "source": "#### Json", "id": "8f3cfe799aaa9b90" }, { "metadata": { "ExecuteTime": { "end_time": "2025-08-10T09:21:37.415399Z", "start_time": "2025-08-10T09:21:37.412530Z" } }, "cell_type": "code", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Writing config.json\n" ] } ], "execution_count": 55, "source": [ "%%writefile config.json\n", "{\n", " \"database\": {\n", " \"url\": \"postgresql://user:pass@localhost:5432/db\",\n", " \"timeout\": 30\n", " },\n", " \"logging\": {\n", " \"level\": \"DEBUG\"\n", " }\n", "}" ], "id": "772a457da96f850e" }, { "metadata": { "ExecuteTime": { "end_time": "2025-08-10T09:22:05.849150Z", "start_time": "2025-08-10T09:22:05.846332Z" } }, "cell_type": "code", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "{'database': {'url': 'postgresql://user:pass@localhost:5432/db', 'timeout': 30}, 'logging': {'level': 'DEBUG'}}\n", "postgresql://user:pass@localhost:5432/db\n" ] } ], "execution_count": 56, "source": [ "import json\n", "\n", "with open('config.json', 'r') as f:\n", " config = json.load(f)\n", "\n", "print(config)\n", "print(config['database']['url'])" ], "id": "953de0c4c9746469" }, { "metadata": {}, "cell_type": "markdown", "source": "#### INI", "id": "b75a6ef6ee2dca9c" }, { "metadata": { "ExecuteTime": { "end_time": "2025-08-10T09:23:26.542761Z", "start_time": "2025-08-10T09:23:26.539349Z" } }, "cell_type": "code", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Writing config.ini\n" ] } ], "execution_count": 58, "source": [ "%%writefile config.ini\n", "[database]\n", "url = postgresql://user:pass@localhost:5432/db\n", "timeout = 30\n", "\n", "[logging]\n", "level = DEBUG" ], "id": "350a8c0d9ee389de" }, { "metadata": { "ExecuteTime": { "end_time": "2025-08-10T09:23:49.091077Z", "start_time": "2025-08-10T09:23:49.087791Z" } }, "cell_type": "code", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "\n", "postgresql://user:pass@localhost:5432/db\n", "DEBUG\n" ] } ], "execution_count": 60, "source": [ "from configparser import ConfigParser\n", "\n", "config = ConfigParser()\n", "config.read(\"config.ini\")\n", "\n", "print(config)\n", "print(config.get(\"database\", \"url\"))\n", "print(config.get(\"logging\", \"level\"))" ], "id": "8ae24cc1c29c5b8b" }, { "metadata": {}, "cell_type": "markdown", "source": [ "## Paths\n", "\n", "A filesystem is the OS abstraction that maps names to stored data. It has two kinds of objects\n", "\n", "- Files: name, content, metadata\n", "- Directories: special files which content is entries to other files" ], "id": "a98aa75114d9d926" }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-23T10:51:11.842223600Z", "start_time": "2026-09-23T10:51:11.780775700Z" } }, "cell_type": "code", "source": [ "from pathlib import Path\n", "\n", "cwd = Path.cwd()\n", "print(cwd)" ], "id": "f7ac41da3f9deafd", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "C:\\Users\\Carlos.Alfonsobasab\\Work\\Python_TA\\seminars\\sem_03\n" ] } ], "execution_count": 9 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-23T10:51:12.761381100Z", "start_time": "2026-09-23T10:51:12.700187Z" } }, "cell_type": "code", "source": [ "tmp = cwd / \"tmp\"\n", "tmp.mkdir(exist_ok=True) # idempotent\n", "\n", "notes_file = tmp / \"notes.txt\"\n", "notes_file.write_text(\"hello\\n\")" ], "id": "d1d051e19c313a46", "outputs": [ { "data": { "text/plain": [ "6" ] }, "execution_count": 10, "metadata": {}, "output_type": "execute_result" } ], "execution_count": 10 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-23T10:52:28.328472300Z", "start_time": "2026-09-23T10:52:28.272422500Z" } }, "cell_type": "code", "source": [ "relative = notes_file.relative_to(cwd)\n", "\n", "print(notes_file)\n", "print(relative)\n", "print(notes_file.is_absolute(), relative.is_absolute())" ], "id": "77e27c1bfb4c5caf", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "C:\\Users\\Carlos.Alfonsobasab\\Work\\Python_TA\\seminars\\sem_03\\tmp\\notes.txt\n", "tmp\\notes.txt\n", "True False\n" ] } ], "execution_count": 16 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-23T10:52:29.409368800Z", "start_time": "2026-09-23T10:52:29.351934700Z" } }, "cell_type": "code", "source": [ "print(notes_file.name)\n", "print(notes_file.stem)\n", "print(notes_file.suffix)" ], "id": "dc02c7bbd7a4614d", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "notes.txt\n", "notes\n", ".txt\n" ] } ], "execution_count": 17 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-23T10:51:54.447622Z", "start_time": "2026-09-23T10:51:54.382892600Z" } }, "cell_type": "code", "source": [ "print(notes_file.parent)\n", "print(notes_file.parent.parent)\n", "print(list(relative.parents))" ], "id": "34512e476858aafa", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "C:\\Users\\Carlos.Alfonsobasab\\Work\\Python_TA\\seminars\\sem_03\\tmp\n", "C:\\Users\\Carlos.Alfonsobasab\\Work\\Python_TA\\seminars\\sem_03\n", "[WindowsPath('tmp'), WindowsPath('.')]\n" ] } ], "execution_count": 14 }, { "metadata": {}, "cell_type": "code", "outputs": [], "execution_count": null, "source": [ "notes = tmp / \"notes.txt\"\n", "notes.write_text(\"hello\\n\", encoding=\"utf-8\") # works with open\n", "print(notes.read_text(encoding=\"utf-8\"))" ], "id": "aaee631dc2549249" }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-23T10:52:35.750462Z", "start_time": "2026-09-23T10:52:35.686288800Z" } }, "cell_type": "code", "source": [ "notes_file.unlink(missing_ok=True) # idempotent\n", "\n", "print(notes_file.exists())" ], "id": "381de7b01b9d5688", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "False\n" ] } ], "execution_count": 18 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-23T10:57:37.207539500Z", "start_time": "2026-09-23T10:57:37.134342600Z" } }, "cell_type": "code", "source": "type(notes_file)", "id": "71cf70cb9a1bca4f", "outputs": [ { "data": { "text/plain": [ "pathlib.WindowsPath" ] }, "execution_count": 19, "metadata": {}, "output_type": "execute_result" } ], "execution_count": 19 }, { "metadata": {}, "cell_type": "markdown", "source": "`Path()` creates a `PosixPath` or a `WindowsPath` depending on the OS, which follow different rules:", "id": "ea7489934e442cd2" }, { "metadata": {}, "cell_type": "markdown", "source": [ "| | POSIX (Linux, macOS) | Windows |\n", "|---|---|---|\n", "| Root | single `/` | per drive (`C:\\`), or UNC `\\\\server\\share\\` |\n", "| Separator | `/` | `\\` (also accepts `/`) |\n", "| Case | sensitive (macOS: insensitive by default) | insensitive |\n", "| Name encoding | raw bytes | UTF-16 |\n", "| Forbidden in names | `/` and NUL | `< > : \" / \\ \\| ? *`" ], "id": "fbd8f6f979b7319a" }, { "metadata": {}, "cell_type": "markdown", "source": "traversing paths", "id": "24444878f2d3e880" }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-23T19:55:03.516995Z", "start_time": "2026-09-23T19:55:03.325047400Z" } }, "cell_type": "code", "source": "print(sum(1 for p in cwd.iterdir() if p.is_file()))", "id": "7be3b6ef52cd6761", "outputs": [ { "ename": "NameError", "evalue": "name 'cwd' is not defined", "output_type": "error", "traceback": [ "\u001B[31m---------------------------------------------------------------------------\u001B[39m", "\u001B[31mNameError\u001B[39m Traceback (most recent call last)", "\u001B[36mCell\u001B[39m\u001B[36m \u001B[39m\u001B[32mIn[1]\u001B[39m\u001B[32m, line 1\u001B[39m\n\u001B[32m----> \u001B[39m\u001B[32m1\u001B[39m print(sum(\u001B[32m1\u001B[39m \u001B[38;5;28;01mfor\u001B[39;00m p \u001B[38;5;28;01min\u001B[39;00m cwd.iterdir() \u001B[38;5;28;01mif\u001B[39;00m p.is_file()))\n", "\u001B[31mNameError\u001B[39m: name 'cwd' is not defined" ] } ], "execution_count": 1 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-23T11:30:13.830996500Z", "start_time": "2026-09-23T11:30:13.673946800Z" } }, "cell_type": "code", "source": "print(sum(len(files) for current_dir, dirs, files in cwd.walk()))", "id": "dc0f43dc2cba4c90", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "9973\n" ] } ], "execution_count": 22 }, { "metadata": {}, "cell_type": "markdown", "source": [ "Task\n", "\n", "## Task: quarantine watcher\n", "\n", "A service drops user uploads into `tmp/watched/`. Write a script `quarantine.py` that every second:\n", "\n", "1. scans all files in `tmp/watched/`,\n", "2. finds files with a dangerous extension (`.exe`, `.bat`, `.js`, `.ps1`),\n", "3. moves them to `tmp/quarantine/` and prints the name of each moved file." ], "id": "ad432edea4f53ec4" }, { "metadata": {}, "cell_type": "code", "outputs": [], "execution_count": null, "source": [ "BASE_DIR = Path(__file__).resolve().parent / \"tmp\"\n", "WATCHED = BASE_DIR / \"watched\"\n", "QUARANTINE = BASE_DIR / \"quarantine\"\n", "BLOCKED = {\".exe\", \".bat\", \".js\", \".ps1\"}\n", "INTERVAL_SECONDS = 1" ], "id": "598c4ca9cb3c91c1" }, { "metadata": {}, "cell_type": "code", "outputs": [], "execution_count": null, "source": [ "def is_suspicious(path : Path):\n", " pass\n", "\n", "def quarantine(suspicious_file : Path):\n", " QUARANTINE.mkdir(exist_ok=True)\n", " pass\n", "\n", "def scan():\n", " # for dirpath, _, filenames in WATCHED.walk():\n", " pass\n", "\n", "def main():\n", " while True:\n", " time.sleep(INTERVAL_SECONDS)" ], "id": "440b36dd911a111d" }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-23T20:01:55.339142900Z", "start_time": "2026-09-23T20:01:55.261586900Z" } }, "cell_type": "code", "source": [ "%%writefile quarantine_watcher.py\n", "\n", "#solution\n", "def is_suspicious(path : Path):\n", " return path.is_file() and path.suffix.lower() in BLOCKED\n", "\n", "def quarantine(suspicious_file : Path):\n", " QUARANTINE.mkdir(exist_ok=True)\n", " suspicious_file.relative_to(WATCHED).rename(QUARANTINE / suspicious_file)\n", " print(suspicious_file.name)\n", "\n", "def scan():\n", " for dirpath, _, filenames in WATCHED.walk():\n", " for name in filenames:\n", " path = dirpath / name\n", " if is_suspicious(path):\n", " quarantine(path)\n", "\n", "def main():\n", " while True:\n", " scan()\n", " time.sleep(INTERVAL_SECONDS)\n", "\n", "if __name__ == \"__main__\":\n", " main()" ], "id": "42ec188e249d9a9f", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Writing quarantine_watcher.py\n" ] } ], "execution_count": 2 }, { "metadata": {}, "cell_type": "markdown", "source": [ "## Sys\n", "\n", "The sys module provides access to some variables used or maintained by the interpreter and to functions that interact strongly with the interpreter.\n", "\n", "Stages of the python interpreter:\n", "\n", "- Runtime initialization and configuration\n", "- Compilation\n", "- Execution\n", "- Output\n", "\n", "We will only cover just a small subset of the functionalities.\n", "\n", "You can learn more in: https://docs.python.org/3/library/sys.html\n" ], "id": "984ae2a2516bffa" }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T18:12:38.457859400Z", "start_time": "2026-09-22T18:12:38.348332700Z" } }, "cell_type": "code", "source": [ "import sys\n", "\n", "print(\"executable :\", sys.executable)\n", "print(\"prefix :\", sys.prefix)\n", "print(\"base_prefix :\", sys.base_prefix)\n", "print(\"virtualenv :\", sys.prefix != sys.base_prefix)\n" ], "id": "4c115846f7b59159", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "executable : C:\\Users\\Carlos.Alfonsobasab\\Work\\Python_TA\\seminars\\sem_03\\.venv\\Scripts\\python.exe\n", "prefix : C:\\Users\\Carlos.Alfonsobasab\\Work\\Python_TA\\seminars\\sem_03\\.venv\n", "base_prefix : C:\\Users\\Carlos.Alfonsobasab\\AppData\\Roaming\\uv\\python\\cpython-3.14.2-windows-x86_64-none\n", "virtualenv : True\n" ] }, { "data": { "text/plain": [ "{'sys': ,\n", " 'builtins': ,\n", " '_frozen_importlib': ,\n", " '_imp': ,\n", " '_thread': ,\n", " '_warnings': ,\n", " '_weakref': ,\n", " 'winreg': ,\n", " '_io': ,\n", " 'marshal': ,\n", " 'nt': ,\n", " '_frozen_importlib_external': ,\n", " 'time': ,\n", " 'zipimport': ,\n", " '_codecs': ,\n", " 'codecs': ,\n", " 'encodings.aliases': ,\n", " 'encodings._win_cp_codecs': ,\n", " 'encodings': ,\n", " 'encodings.utf_8': ,\n", " '_signal': ,\n", " '__main__': ,\n", " '_abc': ,\n", " 'abc': ,\n", " '_stat': 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,\n", " 'ipykernel.comm': ,\n", " 'ipykernel.compiler': ,\n", " 'packaging': ,\n", " 'packaging.version': ,\n", " 'ipykernel.eventloops': ,\n", " 'IPython.core.magics._table': ,\n", " 'IPython.core.magics': ,\n", " 'IPython.core.magics.code': ,\n", " 'ipykernel.displayhook': ,\n", " 'ipykernel.zmqshell': ,\n", " 'IPython.utils.generics': ,\n", " 'IPython.core.completer': ,\n", " 'ipykernel.ipkernel': ,\n", " 'ipykernel.parentpoller': ,\n", " 'ipykernel.socket_pair': ,\n", " 'ipykernel.subshell': ,\n", " 'ipykernel.subshell_manager': ,\n", " 'ipykernel.shellchannel': ,\n", " 'ipykernel.kernelapp': ,\n", " 'cmd': ,\n", " 'bdb': ,\n", " 'code': ,\n", " '_pyrepl': ,\n", " 'unicodedata': ,\n", " '_pyrepl.types': ,\n", " '_pyrepl.trace': ,\n", " '_pyrepl.utils': ,\n", " 'pdb': ,\n", " 'IPython.core.debugger_backport': ,\n", " 'IPython.core.debugger': ,\n", " 'encodings.cp1252': ,\n", " 'tornado.platform': ,\n", " 'tornado.gen': ,\n", " 'tornado.platform.asyncio': ,\n", " 'faulthandler': ,\n", " 'tornado.locks': ,\n", " 'tornado.queues': ,\n", " 'debugpy._version': ,\n", " 'debugpy.public_api': ,\n", " 'debugpy': ,\n", " 'debugpy._vendored._util': ,\n", " 'debugpy._vendored': ,\n", " '_pydevd_bundle': ,\n", " 'encodings.ascii': ,\n", " 'encodings.latin_1': ,\n", " 'stringprep': ,\n", " 'encodings.idna': ,\n", " '_pydevd_bundle.pydevd_vm_type': ,\n", " '_pydev_bundle': ,\n", " 'xmlrpc': ,\n", " 'http': ,\n", " 'email.errors': ,\n", " 'email.quoprimime': ,\n", " 'email.base64mime': ,\n", " 'quopri': ,\n", " 'email.encoders': ,\n", " 'email.charset': ,\n", " 'email.header': ,\n", " 'email._parseaddr': ,\n", " 'email.utils': ,\n", " 'email._policybase': ,\n", " 'email.feedparser': ,\n", " 'email.parser': ,\n", " 'email._encoded_words': ,\n", " 'email.iterators': ,\n", " 'email.message': ,\n", " 'http.client': ,\n", " 'xml': ,\n", " 'xml.parsers': ,\n", " 'pyexpat.errors': ,\n", " 'pyexpat.model': ,\n", " 'pyexpat': ,\n", " 'xml.parsers.expat.model': ,\n", " 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,\n", " '_pydevd_bundle.pydevd_filtering': ,\n", " '_pydevd_bundle.pydevd_io': ,\n", " '_pydevd_bundle.pydevd_defaults': ,\n", " '_pydevd_bundle.pydevd_utils': ,\n", " '_pydevd_bundle.pydevd_runpy': ,\n", " '_pydev_bundle._pydev_tipper_common': ,\n", " '_pydev_bundle._pydev_imports_tipper': ,\n", " '_pydev_bundle._pydev_calltip_util': ,\n", " '_pydevd_bundle.pydevd_safe_repr': ,\n", " '_pydevd_bundle.pydevd_resolver': ,\n", " '_pydevd_bundle.pydevd_extension_api': ,\n", " '_pydevd_bundle.pydevd_xml': ,\n", " '_pydevd_bundle.pydevd_additional_thread_info_regular': ,\n", " '_pydevd_bundle.pydevd_additional_thread_info': ,\n", " '_pydevd_sys_monitoring': ,\n", " '_pydevd_bundle.pydevd_dont_trace': ,\n", " '_pydevd_frame_eval.vendored': ,\n", " '_pydevd_frame_eval.vendored.bytecode.flags': ,\n", " '_pydevd_frame_eval.vendored.bytecode.instr': ,\n", " '_pydevd_frame_eval.vendored.bytecode.bytecode': ,\n", " '_pydevd_frame_eval.vendored.bytecode.concrete': ,\n", " '_pydevd_frame_eval.vendored.bytecode.cfg': ,\n", " '_pydevd_frame_eval.vendored.bytecode': ,\n", " '_pydevd_bundle.pydevd_bytecode_utils': ,\n", " '_pydevd_bundle.pydevd_frame': ,\n", " '_pydevd_bundle.pydevd_trace_dispatch_regular': ,\n", " '_pydevd_bundle.pydevd_trace_dispatch': ,\n", " '_pydevd_bundle.pydevd_import_class': ,\n", " '_pydevd_bundle.pydevd_breakpoints': ,\n", " '_pydevd_sys_monitoring._pydevd_sys_monitoring': ,\n", " '_pydevd_sys_monitoring.pydevd_sys_monitoring': ,\n", " '_pydevd_bundle.pydevd_thread_lifecycle': ,\n", " '_pydevd_bundle.pydevd_save_locals': ,\n", " '_pydev_bundle.pydev_monkey': ,\n", " 'pydevd_tracing': ,\n", " '_pydevd_bundle.pydevd_collect_bytecode_info': ,\n", " '_pydevd_bundle.pydevd_daemon_thread': ,\n", " '_pydevd_bundle.pydevd_timeout': ,\n", " '_pydevd_bundle.pydevd_vars': ,\n", " '_pydev_bundle.pydev_console_utils': ,\n", " '_pydevd_bundle.pydevd_custom_frames': ,\n", " '_pydevd_bundle.pydevd_net_command': ,\n", " '_pydevd_bundle.pydevconsole_code': ,\n", " '_pydev_bundle.pydev_umd': ,\n", " 'pydevconsole': ,\n", " '_pydev_bundle._pydev_completer': ,\n", " '_pydevd_bundle.pydevd_net_command_factory_xml': ,\n", " '_pydevd_frame_eval.pydevd_frame_eval_main': ,\n", " '_pydevd_bundle.pydevd_source_mapping': ,\n", " '_pydevd_bundle.pydevd_concurrency_analyser': ,\n", " '_pydevd_bundle.pydevd_concurrency_analyser.pydevd_thread_wrappers': ,\n", " '_pydevd_bundle.pydevd_concurrency_analyser.pydevd_concurrency_logger': ,\n", " '_pydevd_bundle._debug_adapter': ,\n", " '_pydevd_bundle._debug_adapter.pydevd_schema_log': ,\n", " '_pydevd_bundle._debug_adapter.pydevd_base_schema': ,\n", " '_pydevd_bundle._debug_adapter.pydevd_schema': ,\n", " '_pydevd_bundle.custom': ,\n", " 'pycharm_tables': ,\n", " 'pycharm_tables.pydevd_tables': ,\n", " '_pydevd_bundle.custom.pydevd_tables': ,\n", " '_pydevd_bundle.pydevd_reload': ,\n", " '_pydev_bundle.fsnotify': ,\n", " '_pydevd_bundle.pydevd_console': ,\n", " '_pydevd_bundle.custom.pydevd_constants': ,\n", " '_pydevd_bundle.custom.pydevd_custom_frames': ,\n", " '_pydevd_bundle.custom.pydevd_user_type_renderers_utils': ,\n", " '_pydevd_bundle.custom.pydevd_asyncio_provider': ,\n", " '_pydevd_bundle.custom.pydevd_utils': ,\n", " '_pydevd_bundle.custom.pydevd_vars': ,\n", " '_pydevd_bundle.pydevd_comm': ,\n", " '_pydevd_bundle.pydevd_net_command_factory_json': ,\n", " '_pydevd_bundle.pydevd_api': ,\n", " '_pydevd_bundle.pydevd_json_debug_options': ,\n", " '_pydevd_bundle.pydevd_process_net_command_json': ,\n", " '_pydevd_bundle.pydevd_traceproperty': ,\n", " '_pydevd_bundle.pydevd_process_net_command': ,\n", " '_pydevd_bundle.pydevd_suspended_frames': ,\n", " 'pydevd_plugins.pydevd_line_validation': ,\n", " 'pydevd_plugins.django_debug': ,\n", " 'pydevd_plugins.jinja2_debug': ,\n", " '_pydevd_bundle.pydevd_plugin_utils': ,\n", " 'pydevd_plugins.extensions.types': ,\n", " '_pydevd_bundle.custom.pydevd_repr_utils': ,\n", " 'pydevd_plugins.extensions.types.pydevd_helpers': ,\n", " 'pydevd_plugins.extensions.types.pydevd_plugin_numpy_types': ,\n", " 'pydevd_plugins.extensions.types.pydevd_plugin_pandas_types': ,\n", " 'pydevd_plugins.extensions.types.pydevd_plugins_django_form_str': ,\n", " 'pydevd_plugins.extensions.types.pydevd_plugin_repr_lib': ,\n", " 'pydevd': ,\n", " 'debugpy._vendored.force_pydevd': ,\n", " 'debugpy.server': ,\n", " 'debugpy.adapter': ,\n", " 'debugpy.common': ,\n", " 'debugpy.common.json': ,\n", " 'debugpy.common.timestamp': ,\n", " 'debugpy.common.util': ,\n", " 'debugpy.common.log': ,\n", " 'debugpy.common.sockets': ,\n", " 'debugpy.server.api': ,\n", " 'ipykernel.debugger': ,\n", " 'IPython.utils.wildcard': ,\n", " 'IPython.core.oinspect': ,\n", " '_sqlite3': ,\n", " 'sqlite3.dbapi2': ,\n", " 'sqlite3': ,\n", " 'IPython.core.completerlib': ,\n", " 'IPython.extensions': ,\n", " 'IPython.extensions.storemagic': ,\n", " 'IPython.core.logger': ,\n", " 'executing._utils': ,\n", " 'executing._exceptions': ,\n", " 'executing._position_node_finder': ,\n", " 'executing.executing': ,\n", " 'executing._pytest_utils': ,\n", " 'executing.version': ,\n", " 'executing': ,\n", " 'asttokens.line_numbers': ,\n", " 'asttokens.util': ,\n", " 'asttokens.asttokens': ,\n", " 'asttokens': ,\n", " 'fractions': ,\n", " 'pure_eval.utils': ,\n", " 'pure_eval.my_getattr_static': ,\n", " 'pure_eval.core': ,\n", " 'pure_eval.version': ,\n", " 'pure_eval': ,\n", " 'stack_data.utils': ,\n", " 'stack_data.core': ,\n", " 'stack_data.formatting': ,\n", " 'stack_data.serializing': ,\n", " 'stack_data.version': ,\n", " 'stack_data': ,\n", " 'pygments.formatters._mapping': ,\n", " 'pygments.plugin': ,\n", " 'pygments.util': ,\n", " 'pygments.formatters': ,\n", " 'pygments.styles._mapping': ,\n", " 'pygments.styles': ,\n", " 'pygments.formatter': ,\n", " 'pygments.console': ,\n", " 'pygments.formatters.terminal256': ,\n", " 'pycharm_jupyter': ,\n", " 'debugpy._vendored.pydevd': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle.pydevd_resolver': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle.pydevd_vars': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle.pydevd_xml': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle.pydevd_utils': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle.pydevd_safe_repr': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle.pydevd_constants': ,\n", " 'pycharm_jupyter.runtime_vars': ,\n", " 'IPython.core.magic_arguments': ,\n", " 'IPython.core.magics.osm': ,\n", " 'gc': ,\n", " 'timeit': ,\n", " 'IPython.utils.module_paths': ,\n", " 'IPython.core.magics.ast_mod': ,\n", " 'IPython.core.magics.execution': ,\n", " '_csv': ,\n", " 'csv': }" ] }, "execution_count": 18, "metadata": {}, "output_type": "execute_result" } ], "execution_count": 18 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T18:03:01.072936600Z", "start_time": "2026-09-22T18:03:00.987987600Z" } }, "cell_type": "code", "source": [ "# We can use the executable to spawn Python subprocesses\n", "import subprocess\n", "\n", "subprocess.run([sys.executable, \"--version\"])" ], "id": "74072834fbafac3d", "outputs": [ { "data": { "text/plain": [ "CompletedProcess(args=['C:\\\\Users\\\\Carlos.Alfonsobasab\\\\Work\\\\Python_TA\\\\seminars\\\\sem_03\\\\.venv\\\\Scripts\\\\python.exe', '--version'], returncode=0)" ] }, "execution_count": 15, "metadata": {}, "output_type": "execute_result" } ], "execution_count": 15 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T18:12:52.970330200Z", "start_time": "2026-09-22T18:12:52.888448700Z" } }, "cell_type": "code", "source": "sys.modules", "id": "211b8ab901cc0eda", "outputs": [ { "data": { "text/plain": [ "{'sys': ,\n", " 'builtins': ,\n", " '_frozen_importlib': ,\n", " '_imp': ,\n", " '_thread': ,\n", " '_warnings': ,\n", " '_weakref': ,\n", " 'winreg': ,\n", " '_io': ,\n", " 'marshal': ,\n", " 'nt': ,\n", " '_frozen_importlib_external': ,\n", " 'time': ,\n", 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,\n", " 'pycharm_tables.pydevd_tables': ,\n", " '_pydevd_bundle.custom.pydevd_tables': ,\n", " '_pydevd_bundle.pydevd_reload': ,\n", " '_pydev_bundle.fsnotify': ,\n", " '_pydevd_bundle.pydevd_console': ,\n", " '_pydevd_bundle.custom.pydevd_constants': ,\n", " '_pydevd_bundle.custom.pydevd_custom_frames': ,\n", " '_pydevd_bundle.custom.pydevd_user_type_renderers_utils': ,\n", " '_pydevd_bundle.custom.pydevd_asyncio_provider': ,\n", " '_pydevd_bundle.custom.pydevd_utils': ,\n", " '_pydevd_bundle.custom.pydevd_vars': ,\n", " '_pydevd_bundle.pydevd_comm': ,\n", " '_pydevd_bundle.pydevd_net_command_factory_json': ,\n", " '_pydevd_bundle.pydevd_api': ,\n", " '_pydevd_bundle.pydevd_json_debug_options': ,\n", " '_pydevd_bundle.pydevd_process_net_command_json': ,\n", " '_pydevd_bundle.pydevd_traceproperty': ,\n", " '_pydevd_bundle.pydevd_process_net_command': ,\n", " '_pydevd_bundle.pydevd_suspended_frames': ,\n", " 'pydevd_plugins.pydevd_line_validation': ,\n", " 'pydevd_plugins.django_debug': ,\n", " 'pydevd_plugins.jinja2_debug': ,\n", " '_pydevd_bundle.pydevd_plugin_utils': ,\n", " 'pydevd_plugins.extensions.types': ,\n", " '_pydevd_bundle.custom.pydevd_repr_utils': ,\n", " 'pydevd_plugins.extensions.types.pydevd_helpers': ,\n", " 'pydevd_plugins.extensions.types.pydevd_plugin_numpy_types': ,\n", " 'pydevd_plugins.extensions.types.pydevd_plugin_pandas_types': ,\n", " 'pydevd_plugins.extensions.types.pydevd_plugins_django_form_str': ,\n", " 'pydevd_plugins.extensions.types.pydevd_plugin_repr_lib': ,\n", " 'pydevd': ,\n", " 'debugpy._vendored.force_pydevd': ,\n", " 'debugpy.server': ,\n", " 'debugpy.adapter': ,\n", " 'debugpy.common': ,\n", " 'debugpy.common.json': ,\n", " 'debugpy.common.timestamp': ,\n", " 'debugpy.common.util': ,\n", " 'debugpy.common.log': ,\n", " 'debugpy.common.sockets': ,\n", " 'debugpy.server.api': ,\n", " 'ipykernel.debugger': ,\n", " 'IPython.utils.wildcard': ,\n", " 'IPython.core.oinspect': ,\n", " '_sqlite3': ,\n", " 'sqlite3.dbapi2': ,\n", " 'sqlite3': ,\n", " 'IPython.core.completerlib': ,\n", " 'IPython.extensions': ,\n", " 'IPython.extensions.storemagic': ,\n", " 'IPython.core.logger': ,\n", " 'executing._utils': ,\n", " 'executing._exceptions': ,\n", " 'executing._position_node_finder': ,\n", " 'executing.executing': ,\n", " 'executing._pytest_utils': ,\n", " 'executing.version': ,\n", " 'executing': ,\n", " 'asttokens.line_numbers': ,\n", " 'asttokens.util': ,\n", " 'asttokens.asttokens': ,\n", " 'asttokens': ,\n", " 'fractions': ,\n", " 'pure_eval.utils': ,\n", " 'pure_eval.my_getattr_static': ,\n", " 'pure_eval.core': ,\n", " 'pure_eval.version': ,\n", " 'pure_eval': ,\n", " 'stack_data.utils': ,\n", " 'stack_data.core': ,\n", " 'stack_data.formatting': ,\n", " 'stack_data.serializing': ,\n", " 'stack_data.version': ,\n", " 'stack_data': ,\n", " 'pygments.formatters._mapping': ,\n", " 'pygments.plugin': ,\n", " 'pygments.util': ,\n", " 'pygments.formatters': ,\n", " 'pygments.styles._mapping': ,\n", " 'pygments.styles': ,\n", " 'pygments.formatter': ,\n", " 'pygments.console': ,\n", " 'pygments.formatters.terminal256': ,\n", " 'pycharm_jupyter': ,\n", " 'debugpy._vendored.pydevd': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle.pydevd_resolver': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle.pydevd_vars': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle.pydevd_xml': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle.pydevd_utils': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle.pydevd_safe_repr': ,\n", " 'debugpy._vendored.pydevd._pydevd_bundle.pydevd_constants': ,\n", " 'pycharm_jupyter.runtime_vars': ,\n", " 'IPython.core.magic_arguments': ,\n", " 'IPython.core.magics.osm': ,\n", " 'gc': ,\n", " 'timeit': ,\n", " 'IPython.utils.module_paths': ,\n", " 'IPython.core.magics.ast_mod': ,\n", " 'IPython.core.magics.execution': ,\n", " '_csv': ,\n", " 'csv': ,\n", " 'zmq.utils.garbage': }" ] }, "execution_count": 19, "metadata": {}, "output_type": "execute_result" } ], "execution_count": 19 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T18:13:37.887397800Z", "start_time": "2026-09-22T18:13:37.823851500Z" } }, "cell_type": "code", "source": [ "print(\"outside except:\", sys.exc_info())\n", "\n", "try:\n", " 1 / 0\n", "except ZeroDivisionError:\n", " exc_type, exc_value, exc_tb = sys.exc_info()\n", " print(\"inside except :\", exc_type.__name__, \"|\", exc_value)" ], "id": "fcec832bfad9cf5", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "outside except: (None, None, None)\n", "inside except : ZeroDivisionError | division by zero\n" ] } ], "execution_count": 20 }, { "metadata": {}, "cell_type": "markdown", "source": "### CLI", "id": "786eceebc8814492" }, { "metadata": {}, "cell_type": "markdown", "source": "![image.png](assets/img.png)", "id": "dbe822ddb4cbce38" }, { "metadata": {}, "cell_type": "code", "outputs": [], "execution_count": null, "source": [ "%%writefile echo_args.py\n", "import sys\n", "\n", "print(\"script :\", sys.argv[0])\n", "print(\"args :\", sys.argv[1:])" ], "id": "f2d95b67457a327f" }, { "metadata": {}, "cell_type": "code", "outputs": [], "execution_count": null, "source": [ "%%writefile flushdemo.py\n", "import sys, time\n", "\n", "for i in range(3):\n", " sys.stdout.write(f\"step {i} \")\n", " sys.stdout.flush()\n", " time.sleep(0.5)\n", "print()" ], "id": "3a5c4dbde20bfdfe" }, { "metadata": {}, "cell_type": "markdown", "source": "Grep like cli tool implementation", "id": "b67453590d5a00d3" }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T17:50:14.734585600Z", "start_time": "2026-09-22T17:50:14.697129600Z" } }, "cell_type": "code", "source": [ "%%writefile mygrep.py\n", "\n", "import sys\n", "\n", "USAGE = \"usage: mygrep.py PATTERN [--limit N] [--ignore-case]\"\n", "\n", "\n", "def print_usage_and_exit(message):\n", " print(f\"{USAGE}\\nmygrep.py: {message}\", file=sys.stderr)\n", " sys.exit(2)\n", "\n", "\n", "def get_parsed_limit_or_fail(args):\n", " if not args or not args[0].isdigit():\n", " print_usage_and_exit(\"--limit must be a non-negative integer\")\n", " return int(args.pop(0))\n", "\n", "\n", "def get_parsed_args(args):\n", " pattern, limit, ignore_case = None, 0, False\n", " while args:\n", " arg = args.pop(0)\n", " if arg == \"--limit\":\n", " limit = get_parsed_limit_or_fail(args)\n", " elif arg == \"--ignore-case\":\n", " ignore_case = True\n", " elif pattern is None:\n", " pattern = arg\n", " else:\n", " print_usage_and_exit(f\"unexpected argument: {arg}\")\n", " if pattern is None:\n", " print_usage_and_exit(\"PATTERN is required\")\n", " return pattern, limit, ignore_case\n", "\n", "\n", "def main():\n", " pattern, limit, ignore_case = get_parsed_args(sys.argv[1:])\n", " if ignore_case:\n", " pattern = pattern.lower()\n", "\n", " matched = 0\n", " for line in sys.stdin:\n", " text = line.lower() if ignore_case else line\n", " if pattern in text:\n", " print(line, end=\"\")\n", " matched += 1\n", " if matched == limit:\n", " break\n", "\n", " print(f\"{matched} matching lines\", file=sys.stderr)\n", " return 0 if matched else 1\n", "\n", "\n", "if __name__ == \"__main__\":\n", " sys.exit(main())" ], "id": "19ca73c39f953580", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Writing mygrep.py\n" ] } ], "execution_count": 13 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T17:08:20.955546600Z", "start_time": "2026-09-22T17:08:20.616919800Z" } }, "cell_type": "code", "source": [ "# better example\n", "import argparse\n", "import sys\n", "\n", "def get_parsed_args():\n", " parser = argparse.ArgumentParser(\n", " prog=\"mygrep.py\",\n", " description=\"Print stdin lines containing PATTERN.\")\n", " parser.add_argument(\"pattern\")\n", " parser.add_argument(\"--limit\", type=int, default=0, metavar=\"N\",\n", " help=\"stop after N matches (default: no limit)\")\n", " parser.add_argument(\"--ignore-case\", action=\"store_true\")\n", " args = parser.parse_args()\n", " if args.limit < 0:\n", " parser.error(\"--limit must be a non-negative integer\")\n", " return args\n", "\n", "\n", "def main():\n", " args = get_parsed_args()\n", " pattern = args.pattern.lower() if args.ignore_case else args.pattern\n", "\n", " matched = 0\n", " for line in sys.stdin:\n", " text = line.lower() if args.ignore_case else line\n", " if pattern in text:\n", " print(line, end=\"\")\n", " matched += 1\n", " if matched == args.limit:\n", " break\n", "\n", " print(f\"{matched} matching lines\", file=sys.stderr)\n", " return 0 if matched else 1\n", "\n", "\n", "if __name__ == \"__main__\":\n", " sys.exit(main())" ], "id": "dc22504cdf92a123", "outputs": [ { "name": "stderr", "output_type": "stream", "text": [ "\u001B[1;34musage: \u001B[0m\u001B[1;35mmygrep.py\u001B[0m [\u001B[32m-h\u001B[0m] [\u001B[36m--limit \u001B[33mN\u001B[0m] [\u001B[36m--ignore-case\u001B[0m] \u001B[32mpattern\u001B[0m\n", "mygrep.py: error: unrecognized arguments: -f --IPCompleter.use_jedi=False --IPKernelApp.log_level=INFO\n" ] }, { "ename": "SystemExit", "evalue": "2", "output_type": "error", "traceback": [ "An exception has occurred, use %tb to see the full traceback.\n", "\u001B[31mSystemExit\u001B[39m\u001B[31m:\u001B[39m 2\n" ] }, { "name": "stderr", "output_type": "stream", "text": [ "C:\\Users\\Carlos.Alfonsobasab\\Work\\Python_TA\\seminars\\sem_03\\.venv\\Lib\\site-packages\\IPython\\core\\interactiveshell.py:3831: UserWarning: To exit: use 'exit', 'quit', or Ctrl-D.\n", " warn(\"To exit: use 'exit', 'quit', or Ctrl-D.\", stacklevel=1)\n" ] } ], "execution_count": 2 }, { "metadata": {}, "cell_type": "markdown", "source": "You can also use [click](https://click.palletsprojects.com/en/stable/) to create command-line interfaces.", "id": "ce1f98d64a4da8e5" }, { "metadata": {}, "cell_type": "markdown", "source": "## Exceptions", "id": "ec845e9c9ed6e0d0" }, { "metadata": {}, "cell_type": "code", "source": [ "num = int(\"42\")\n", "print(num)\n", "another_num = int(\"42s\")\n", "print(another_num)" ], "id": "f7f98db63b156975", "outputs": [], "execution_count": null }, { "metadata": {}, "cell_type": "code", "source": [ "def infinite_recursion():\n", " return infinite_recursion()\n", "\n", "infinite_recursion()" ], "id": "4eaae5bbc7963832", "outputs": [], "execution_count": null }, { "metadata": { "ExecuteTime": { "end_time": "2025-07-21T09:24:11.441959Z", "start_time": "2025-07-21T09:24:11.375278Z" } }, "cell_type": "code", "outputs": [ { "ename": "FileNotFoundError", "evalue": "[Errno 2] No such file or directory: 'non-existing-file.txt'", "output_type": "error", "traceback": [ "\u001B[0;31m---------------------------------------------------------------------------\u001B[0m", "\u001B[0;31mFileNotFoundError\u001B[0m Traceback (most recent call last)", "Cell \u001B[0;32mIn[52], line 1\u001B[0m\n\u001B[0;32m----> 1\u001B[0m \u001B[38;5;28;01mwith\u001B[39;00m \u001B[38;5;28;43mopen\u001B[39;49m\u001B[43m(\u001B[49m\u001B[38;5;124;43m'\u001B[39;49m\u001B[38;5;124;43mnon-existing-file.txt\u001B[39;49m\u001B[38;5;124;43m'\u001B[39;49m\u001B[43m,\u001B[49m\u001B[43m \u001B[49m\u001B[38;5;124;43m'\u001B[39;49m\u001B[38;5;124;43mr\u001B[39;49m\u001B[38;5;124;43m'\u001B[39;49m\u001B[43m)\u001B[49m \u001B[38;5;28;01mas\u001B[39;00m f:\n\u001B[1;32m 2\u001B[0m content \u001B[38;5;241m=\u001B[39m f\u001B[38;5;241m.\u001B[39mreadline()\n\u001B[1;32m 3\u001B[0m \u001B[38;5;28mprint\u001B[39m(content)\n", "File \u001B[0;32m~/Documents/Msu/DataSpell/python3.10/lib/python3.10/site-packages/IPython/core/interactiveshell.py:324\u001B[0m, in \u001B[0;36m_modified_open\u001B[0;34m(file, *args, **kwargs)\u001B[0m\n\u001B[1;32m 317\u001B[0m \u001B[38;5;28;01mif\u001B[39;00m file \u001B[38;5;129;01min\u001B[39;00m {\u001B[38;5;241m0\u001B[39m, \u001B[38;5;241m1\u001B[39m, \u001B[38;5;241m2\u001B[39m}:\n\u001B[1;32m 318\u001B[0m \u001B[38;5;28;01mraise\u001B[39;00m \u001B[38;5;167;01mValueError\u001B[39;00m(\n\u001B[1;32m 319\u001B[0m \u001B[38;5;124mf\u001B[39m\u001B[38;5;124m\"\u001B[39m\u001B[38;5;124mIPython won\u001B[39m\u001B[38;5;124m'\u001B[39m\u001B[38;5;124mt let you open fd=\u001B[39m\u001B[38;5;132;01m{\u001B[39;00mfile\u001B[38;5;132;01m}\u001B[39;00m\u001B[38;5;124m by default \u001B[39m\u001B[38;5;124m\"\u001B[39m\n\u001B[1;32m 320\u001B[0m \u001B[38;5;124m\"\u001B[39m\u001B[38;5;124mas it is likely to crash IPython. If you know what you are doing, \u001B[39m\u001B[38;5;124m\"\u001B[39m\n\u001B[1;32m 321\u001B[0m \u001B[38;5;124m\"\u001B[39m\u001B[38;5;124myou can use builtins\u001B[39m\u001B[38;5;124m'\u001B[39m\u001B[38;5;124m open.\u001B[39m\u001B[38;5;124m\"\u001B[39m\n\u001B[1;32m 322\u001B[0m )\n\u001B[0;32m--> 324\u001B[0m \u001B[38;5;28;01mreturn\u001B[39;00m \u001B[43mio_open\u001B[49m\u001B[43m(\u001B[49m\u001B[43mfile\u001B[49m\u001B[43m,\u001B[49m\u001B[43m \u001B[49m\u001B[38;5;241;43m*\u001B[39;49m\u001B[43margs\u001B[49m\u001B[43m,\u001B[49m\u001B[43m \u001B[49m\u001B[38;5;241;43m*\u001B[39;49m\u001B[38;5;241;43m*\u001B[39;49m\u001B[43mkwargs\u001B[49m\u001B[43m)\u001B[49m\n", "\u001B[0;31mFileNotFoundError\u001B[0m: [Errno 2] No such file or directory: 'non-existing-file.txt'" ] } ], "execution_count": 52, "source": [ "with open('non-existing-file.txt', 'r') as f:\n", " content = f.readline()\n", " print(content)" ], "id": "a533acd07391e7c4" }, { "metadata": { "ExecuteTime": { "end_time": "2025-07-22T06:06:37.407051Z", "start_time": "2025-07-22T06:06:37.394942Z" } }, "cell_type": "code", "outputs": [ { "ename": "UnsupportedOperation", "evalue": "not readable", "output_type": "error", "traceback": [ "\u001B[0;31m---------------------------------------------------------------------------\u001B[0m", "\u001B[0;31mUnsupportedOperation\u001B[0m Traceback (most recent call last)", "Cell \u001B[0;32mIn[40], line 2\u001B[0m\n\u001B[1;32m 1\u001B[0m \u001B[38;5;28;01mwith\u001B[39;00m \u001B[38;5;28mopen\u001B[39m(\u001B[38;5;124m'\u001B[39m\u001B[38;5;124mnon-existing-file.txt\u001B[39m\u001B[38;5;124m'\u001B[39m, \u001B[38;5;124m'\u001B[39m\u001B[38;5;124mw\u001B[39m\u001B[38;5;124m'\u001B[39m) \u001B[38;5;28;01mas\u001B[39;00m f:\n\u001B[0;32m----> 2\u001B[0m \u001B[38;5;28mprint\u001B[39m(\u001B[43mf\u001B[49m\u001B[38;5;241;43m.\u001B[39;49m\u001B[43mread\u001B[49m\u001B[43m(\u001B[49m\u001B[43m)\u001B[49m)\n", "\u001B[0;31mUnsupportedOperation\u001B[0m: not readable" ] } ], "execution_count": 40, "source": [ "with open('non-existing-file.txt', 'w') as f:\n", " print(f.read())" ], "id": "1b82ff9b440b2ec1" }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-21T06:42:59.479479200Z", "start_time": "2026-09-21T06:42:59.087263800Z" } }, "cell_type": "code", "source": "import non_existing_module", "id": "3d96b6467772dc0b", "outputs": [ { "ename": "ModuleNotFoundError", "evalue": "No module named 'numpy'", "output_type": "error", "traceback": [ "\u001B[31m---------------------------------------------------------------------------\u001B[39m", "\u001B[31mModuleNotFoundError\u001B[39m Traceback (most recent call last)", "\u001B[36mCell\u001B[39m\u001B[36m \u001B[39m\u001B[32mIn[1]\u001B[39m\u001B[32m, line 1\u001B[39m\n\u001B[32m----> \u001B[39m\u001B[32m1\u001B[39m \u001B[38;5;28;01mimport\u001B[39;00m numpy\n", "\u001B[31mModuleNotFoundError\u001B[39m: No module named 'numpy'" ] } ], "execution_count": 1 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-21T07:02:47.268573200Z", "start_time": "2026-09-21T07:02:46.781186200Z" } }, "cell_type": "code", "source": [ "import requests\n", "\n", "response = requests.get(\"https://api.github.com/users/non-existing-user-12345\")\n", "print(response.status_code) # 404\n", "print(response.ok) # False\n", "response.raise_for_status()" ], "id": "515939486b47b0cf", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "404\n", "False\n" ] }, { "ename": "HTTPError", "evalue": "404 Client Error: Not Found for url: https://api.github.com/users/non-existing-user-12345", "output_type": "error", "traceback": [ "\u001B[31m---------------------------------------------------------------------------\u001B[39m", "\u001B[31mHTTPError\u001B[39m Traceback (most recent call last)", "\u001B[36mCell\u001B[39m\u001B[36m \u001B[39m\u001B[32mIn[3]\u001B[39m\u001B[32m, line 6\u001B[39m\n\u001B[32m 2\u001B[39m \n\u001B[32m 3\u001B[39m response = requests.get(\u001B[33m\"https://api.github.com/users/non-existing-user-12345\"\u001B[39m)\n\u001B[32m 4\u001B[39m print(response.status_code) \u001B[38;5;66;03m# 404\u001B[39;00m\n\u001B[32m 5\u001B[39m print(response.ok) \u001B[38;5;66;03m# False\u001B[39;00m\n\u001B[32m----> \u001B[39m\u001B[32m6\u001B[39m response.raise_for_status() \u001B[38;5;66;03m# ← only now\u001B[39;00m\n\u001B[32m 7\u001B[39m \u001B[38;5;66;03m# requests.exceptions.HTTPError: 404 Client Error: Not Found for url: ...\u001B[39;00m\n", "\u001B[36mFile \u001B[39m\u001B[32m~\\Work\\Python_TA\\seminars\\sem_03\\.venv\\Lib\\site-packages\\requests\\models.py:1167\u001B[39m, in \u001B[36mResponse.raise_for_status\u001B[39m\u001B[34m(self)\u001B[39m\n\u001B[32m 1162\u001B[39m http_error_msg = (\n\u001B[32m 1163\u001B[39m \u001B[33mf\u001B[39m\u001B[33m\"\u001B[39m\u001B[38;5;132;01m{\u001B[39;00m\u001B[38;5;28mself\u001B[39m.status_code\u001B[38;5;132;01m}\u001B[39;00m\u001B[33m Server Error: \u001B[39m\u001B[38;5;132;01m{\u001B[39;00mreason\u001B[38;5;132;01m}\u001B[39;00m\u001B[33m for url: \u001B[39m\u001B[38;5;132;01m{\u001B[39;00m\u001B[38;5;28mself\u001B[39m.url\u001B[38;5;132;01m}\u001B[39;00m\u001B[33m\"\u001B[39m\n\u001B[32m 1164\u001B[39m )\n\u001B[32m 1166\u001B[39m \u001B[38;5;28;01mif\u001B[39;00m http_error_msg:\n\u001B[32m-> \u001B[39m\u001B[32m1167\u001B[39m \u001B[38;5;28;01mraise\u001B[39;00m HTTPError(http_error_msg, response=\u001B[38;5;28mself\u001B[39m)\n", "\u001B[31mHTTPError\u001B[39m: 404 Client Error: Not Found for url: https://api.github.com/users/non-existing-user-12345" ] } ], "execution_count": 3 }, { "metadata": {}, "cell_type": "markdown", "source": "Hierarchy of built-in exceptions: https://docs.python.org/3/library/exceptions.html#exception-hierarchy", "id": "d2bcba68daf90505" }, { "metadata": {}, "cell_type": "markdown", "source": [ "
\n", "Exception hierarchy\n", "\n", "```\n", "BaseException\n", " ├── BaseExceptionGroup\n", " ├── GeneratorExit\n", " ├── KeyboardInterrupt\n", " ├── SystemExit\n", " └── Exception\n", " ├── ArithmeticError\n", " │ ├── FloatingPointError\n", " │ ├── OverflowError\n", " │ └── ZeroDivisionError\n", " ├── AssertionError\n", " ├── AttributeError\n", " ├── BufferError\n", " ├── EOFError\n", " ├── ExceptionGroup [BaseExceptionGroup]\n", " ├── ImportError\n", " │ └── ModuleNotFoundError\n", " ├── LookupError\n", " │ ├── IndexError\n", " │ └── KeyError\n", " ├── MemoryError\n", " ├── NameError\n", " │ └── UnboundLocalError\n", " ├── OSError\n", " │ ├── BlockingIOError\n", " │ ├── ChildProcessError\n", " │ ├── ConnectionError\n", " │ │ ├── BrokenPipeError\n", " │ │ ├── ConnectionAbortedError\n", " │ │ ├── ConnectionRefusedError\n", " │ │ └── ConnectionResetError\n", " │ ├── FileExistsError\n", " │ ├── FileNotFoundError\n", " │ ├── InterruptedError\n", " │ ├── IsADirectoryError\n", " │ ├── NotADirectoryError\n", " │ ├── PermissionError\n", " │ ├── ProcessLookupError\n", " │ └── TimeoutError\n", " ├── ReferenceError\n", " ├── RuntimeError\n", " │ ├── NotImplementedError\n", " │ └── RecursionError\n", " ├── StopAsyncIteration\n", " ├── StopIteration\n", " ├── SyntaxError\n", " │ └── IndentationError\n", " │ └── TabError\n", " ├── SystemError\n", " ├── TypeError\n", " ├── ValueError\n", " │ └── UnicodeError\n", " │ ├── UnicodeDecodeError\n", " │ ├── UnicodeEncodeError\n", " │ └── UnicodeTranslateError\n", " └── Warning\n", " ├── BytesWarning\n", " ├── DeprecationWarning\n", " ├── EncodingWarning\n", " ├── FutureWarning\n", " ├── ImportWarning\n", " ├── PendingDeprecationWarning\n", " ├── ResourceWarning\n", " ├── RuntimeWarning\n", " ├── SyntaxWarning\n", " ├── UnicodeWarning\n", " └── UserWarning\n", "```\n", "\n", "
" ], "id": "a0cf8a0275324ba" }, { "metadata": {}, "cell_type": "markdown", "source": "What will this print?", "id": "64f3ce483243432c" }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-21T07:51:57.493969800Z", "start_time": "2026-09-21T07:51:57.453994700Z" } }, "cell_type": "code", "source": [ "f = None\n", "try:\n", " # f = open(\"filename.txt\", 'r') # something dangerous\n", " # div = 1 / 0\n", " print('all good')\n", "except ValueError as e: # scope failure\n", " print(f'Something bad happened: {e!r}')\n", "else: # scope success\n", " print('Nothing bad happened')\n", "finally: # scope exit\n", " if f is not None:\n", " f.close()\n", " print('Print this no matter what')" ], "id": "6afe1d98e2cf1af9", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "all good\n", "Nothing bad happened\n", "Print this no matter what\n" ] } ], "execution_count": 6 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-21T08:15:01.670553600Z", "start_time": "2026-09-21T08:15:01.644995300Z" } }, "cell_type": "code", "source": [ "from requests.exceptions import HTTPError, RetryError\n", "\n", "def get(url):\n", " r = requests.get(url, timeout=5)\n", " r.raise_for_status()\n", "\n", "def get_with_fallback():\n", " try:\n", " get(\"https://api.github.com/users/nobody-12345\") # 404\n", " except HTTPError as primary:\n", " try:\n", " get(\"https://httpbin.org/status/503\") # 503\n", " except HTTPError:\n", " raise RetryError(\"both failed\") from primary" ], "id": "70c4b6292716e14e", "outputs": [], "execution_count": 19 }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-21T08:15:59.345173700Z", "start_time": "2026-09-21T08:15:58.516590900Z" } }, "cell_type": "code", "source": [ "try:\n", " get_with_fallback()\n", "except RetryError as e:\n", " print(\"cause :\", e.__cause__) # 404\n", " print(\"context :\", e.__context__) # 503\n", " print(\"same? :\", e.__cause__ is e.__context__) # False\n", " print(\"suppressed :\", e.__suppress_context__) # True\n" ], "id": "9e08bda6ce052113", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "cause : 404 Client Error: Not Found for url: https://api.github.com/users/nobody-12345\n", "context : 503 Server Error: SERVICE UNAVAILABLE for url: https://httpbin.org/status/503\n", "same? : False\n", "suppressed : True\n" ] } ], "execution_count": 21 }, { "metadata": {}, "cell_type": "markdown", "source": [ "Example 1 - Config loader\n", "\n" ], "id": "74f5f19145043c77" }, { "metadata": {}, "cell_type": "code", "outputs": [], "execution_count": null, "source": [ "import json\n", "from pathlib import Path\n", "\n", "DEFAULTS = {\"timeout\": 30, \"retries\": 3}\n", "\n", "class ConfigError(Exception): ...\n", "\n", "def load_config(path: Path) -> dict:\n", " try:\n", " raw = path.read_text(encoding=\"utf-8\")\n", " except FileNotFoundError:\n", " return dict(DEFAULTS) # no config → defaults\n", " except PermissionError as e:\n", " raise ConfigError(f\"cannot read config {path}: permission denied \") from e\n", " except OSError as e: # IsADirectoryError, broken symlink, ...\n", " raise ConfigError(f\"cannot read {path}\") from e\n", "\n", " try:\n", " return DEFAULTS | json.loads(raw)\n", " except json.JSONDecodeError as e: # subclass of ValueError\n", " raise ConfigError(f\"{path}:{e.lineno}: {e.msg}\") from e" ], "id": "3d1718774f90a14d" }, { "metadata": {}, "cell_type": "markdown", "source": "Example 2: Retrying HTTP requests", "id": "3b056100d31e9082" }, { "metadata": {}, "cell_type": "code", "outputs": [], "execution_count": null, "source": [ "import time\n", "import requests\n", "\n", "RETRYABLE = {429, 500, 502, 503, 504}\n", "\n", "def fetch(url: str, *, attempts: int = 3, backoff: float = 0.5, timeout: float = 5.0):\n", " for attempt in range(1, attempts + 1):\n", " try:\n", " r = requests.get(url, timeout=timeout)\n", " r.raise_for_status()\n", " return r.json()\n", "\n", " except requests.HTTPError as e: # server ANSWERED: 4xx/5xx\n", " status = e.response.status_code\n", " if status not in RETRYABLE or attempt == attempts:\n", " raise # 404/401 — retrying\n", " wait = float(e.response.headers.get(\"Retry-After\") or backoff * 2 ** (attempt - 1))\n", "\n", " except (requests.ConnectionError, requests.Timeout):\n", " if attempt == attempts:\n", " raise\n", " wait = backoff * 2 ** (attempt - 1)\n", "\n", " time.sleep(wait)" ], "id": "c3542e9cd9c65557" }, { "metadata": {}, "cell_type": "markdown", "source": [ "## Context managers\n", "\n", "How can we guarantee that a certain action will run regardless of whether an exception occurred or not?" ], "id": "9a8359d5b2b4045c" }, { "metadata": {}, "cell_type": "code", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Closing file\n", "File closed\n" ] }, { "ename": "RuntimeError", "evalue": "Not today!", "output_type": "error", "traceback": [ "\u001B[0;31m---------------------------------------------------------------------------\u001B[0m", "\u001B[0;31mRuntimeError\u001B[0m Traceback (most recent call last)", "Cell \u001B[0;32mIn[40], line 6\u001B[0m\n\u001B[1;32m 4\u001B[0m fd \u001B[38;5;241m=\u001B[39m \u001B[38;5;28mopen\u001B[39m(\u001B[38;5;124m'\u001B[39m\u001B[38;5;124mmyfile.txt\u001B[39m\u001B[38;5;124m'\u001B[39m, \u001B[38;5;124m'\u001B[39m\u001B[38;5;124mw\u001B[39m\u001B[38;5;124m'\u001B[39m)\n\u001B[1;32m 5\u001B[0m \u001B[38;5;28;01mtry\u001B[39;00m:\n\u001B[0;32m----> 6\u001B[0m \u001B[43mdo_something_dangerous\u001B[49m\u001B[43m(\u001B[49m\u001B[43mfd\u001B[49m\u001B[43m)\u001B[49m\n\u001B[1;32m 7\u001B[0m \u001B[38;5;28;01mfinally\u001B[39;00m:\n\u001B[1;32m 8\u001B[0m \u001B[38;5;28mprint\u001B[39m(\u001B[38;5;124m'\u001B[39m\u001B[38;5;124mClosing file\u001B[39m\u001B[38;5;124m'\u001B[39m)\n", "Cell \u001B[0;32mIn[40], line 2\u001B[0m, in \u001B[0;36mdo_something_dangerous\u001B[0;34m(fd)\u001B[0m\n\u001B[1;32m 1\u001B[0m \u001B[38;5;28;01mdef\u001B[39;00m \u001B[38;5;21mdo_something_dangerous\u001B[39m(fd):\n\u001B[0;32m----> 2\u001B[0m \u001B[38;5;28;01mraise\u001B[39;00m \u001B[38;5;167;01mRuntimeError\u001B[39;00m(\u001B[38;5;124m'\u001B[39m\u001B[38;5;124mNot today!\u001B[39m\u001B[38;5;124m'\u001B[39m)\n", "\u001B[0;31mRuntimeError\u001B[0m: Not today!" ] } ], "execution_count": 40, "source": [ "def do_something_dangerous(fd):\n", " raise RuntimeError('Not today!')\n", "\n", "fd = open('myfile.txt', 'w')\n", "try:\n", " do_something_dangerous(fd)\n", "finally:\n", " print('Closing file')\n", " fd.close()\n", " print('File closed')" ], "id": "66007d6e40c33644" }, { "metadata": {}, "cell_type": "markdown", "source": [ "Context managers provide a convenient way to perform initialization and guaranteed finalization of a “context”.\n", "\n", "``` python\n", "r = acquire_resource()\n", "try:\n", " use_resource(r)\n", "finally:\n", " release_resource(r)\n", "```\n", "\n", "``` python\n", "with acquire_resource() as r:\n", " use_resource(r)\n", "```" ], "id": "776ff329b1a2a8a3" }, { "metadata": {}, "cell_type": "markdown", "source": "### Examples", "id": "6daae05d97333d68" }, { "metadata": {}, "cell_type": "code", "outputs": [ { "ename": "ValueError", "evalue": "I/O operation on closed file.", "output_type": "error", "traceback": [ "\u001B[0;31m---------------------------------------------------------------------------\u001B[0m", "\u001B[0;31mValueError\u001B[0m Traceback (most recent call last)", "Cell \u001B[0;32mIn[1], line 4\u001B[0m\n\u001B[1;32m 2\u001B[0m fd\u001B[38;5;241m.\u001B[39mwrite(\u001B[38;5;124m\"\u001B[39m\u001B[38;5;124mHello\u001B[39m\u001B[38;5;124m\"\u001B[39m)\n\u001B[1;32m 3\u001B[0m \u001B[38;5;66;03m# file is closed\u001B[39;00m\n\u001B[0;32m----> 4\u001B[0m \u001B[43mfd\u001B[49m\u001B[38;5;241;43m.\u001B[39;49m\u001B[43mwrite\u001B[49m\u001B[43m(\u001B[49m\u001B[38;5;124;43m\"\u001B[39;49m\u001B[38;5;124;43mworld\u001B[39;49m\u001B[38;5;124;43m\"\u001B[39;49m\u001B[43m)\u001B[49m\n", "\u001B[0;31mValueError\u001B[0m: I/O operation on closed file." ] } ], "execution_count": 1, "source": [ "with open('filename.txt', 'w') as fd:\n", " fd.write(\"Hello\")\n", "\n", "fd.write(\"world\")" ], "id": "2b4430856b75f7e6" }, { "metadata": { "ExecuteTime": { "end_time": "2026-09-22T15:23:12.490070600Z", "start_time": "2026-09-22T15:23:12.298487400Z" } }, "cell_type": "code", "source": [ "import sqlite3\n", "from contextlib import closing\n", "\n", "with closing(sqlite3.connect(\":memory:\")) as conn:\n", " print(conn.execute(\"SELECT 42\").fetchone())\n", "# connection is closed here\n", "print(conn.execute(\"SELECT 42\"))" ], "id": "d95e38cbb4c7b610", "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "(42,)\n" ] }, { "ename": "ProgrammingError", "evalue": "Cannot operate on a closed database.", "output_type": "error", "traceback": [ "\u001B[31m---------------------------------------------------------------------------\u001B[39m", "\u001B[31mProgrammingError\u001B[39m Traceback (most recent call last)", "\u001B[36mCell\u001B[39m\u001B[36m \u001B[39m\u001B[32mIn[1]\u001B[39m\u001B[32m, line 7\u001B[39m\n\u001B[32m 3\u001B[39m \n\u001B[32m 4\u001B[39m \u001B[38;5;28;01mwith\u001B[39;00m closing(sqlite3.connect(\u001B[33m\":memory:\"\u001B[39m)) \u001B[38;5;28;01mas\u001B[39;00m conn:\n\u001B[32m 5\u001B[39m print(conn.execute(\u001B[33m\"SELECT 42\"\u001B[39m).fetchone())\n\u001B[32m 6\u001B[39m \u001B[38;5;66;03m# connection is closed here\u001B[39;00m\n\u001B[32m----> \u001B[39m\u001B[32m7\u001B[39m print(conn.execute(\u001B[33m\"SELECT 42\"\u001B[39m))\n", "\u001B[31mProgrammingError\u001B[39m: Cannot operate on a closed database." ] } ], "execution_count": 1 }, { "metadata": {}, "cell_type": "markdown", "source": [ "Context managers are objects that implement a special protocol \\\n", "In other words, you can create your own context managers by following the protocol." ], "id": "a6949d6b5954e0c6" }, { "metadata": {}, "cell_type": "code", "outputs": [], "execution_count": 14, "source": [ "import typing as tp\n", "from types import TracebackType\n", "\n", "class MyContextManager:\n", " def __enter__(self) -> tp.Self: # with () as X; analogue of acquire()\n", " # initialize context\n", " # e.g. open a file, connect to a database, etc.\n", " return self\n", "\n", " def __exit__(self,\n", " exc_type: type[BaseException] | None,\n", " exc_value: BaseException | None,\n", " traceback: TracebackType | None) -> bool | None: # analogue of release()\n", " # finalize context\n", " # e.g. close a file, disconnect from a database, etc.\n", " if exc_value is not None:\n", " return True # return True from __exit__ to suppress the exception" ], "id": "a49a11ad5fdaa9a9" }, { "metadata": {}, "cell_type": "markdown", "source": [ "Task\n", "\n", "Implement the atomic_write context manager.\n", "\n", "It should open a temp file and return a file descriptor.\n", "\n", "If any operation on the block fails we should delete the file.\n", "\n", "If the block succeeds we should write the file" ], "id": "a7f3c2bd63f3239" }, { "metadata": {}, "cell_type": "code", "outputs": [], "execution_count": null, "source": [ "from pathlib import Path\n", "\n", "class atomic_write:\n", " \"\"\"Write into a temp file; publish it only if the block succeeded.\"\"\"\n", "\n", " def __init__(self, path, mode=\"w\", **kwargs):\n", " self.path = Path(path)\n", " self.tmp = self.path.with_suffix(self.path.suffix + \".tmp\")\n", " self.mode, self.kwargs = mode, kwargs\n", "\n", " def __enter__(self):\n", " pass\n", "\n", " def __exit__(self, exc_type, exc_value, traceback):\n", " pass # never suppress" ], "id": "9e9523ce7f9a4a25" }, { "metadata": {}, "cell_type": "code", "outputs": [], "execution_count": null, "source": [ "# solution\n", "class atomic_write:\n", " \"\"\"Write into a temp file; publish it only if the block succeeded.\"\"\"\n", "\n", " def __init__(self, path, mode=\"w\", **kwargs):\n", " self.path = Path(path)\n", " self.tmp = self.path.with_suffix(self.path.suffix + \".tmp\")\n", " self.mode, self.kwargs = mode, kwargs\n", "\n", " def __enter__(self):\n", " self.fd = self.tmp.open(self.mode, **self.kwargs)\n", " return self.fd\n", "\n", " def __exit__(self, exc_type, exc_value, traceback):\n", " self.fd.close()\n", " if exc_type is None:\n", " self.tmp.replace(self.path) # atomic rename\n", " else:\n", " self.tmp.unlink(missing_ok=True) # original file untouched\n", " return False # never suppress" ], "id": "8ad749f89878b95a" } ], "metadata": { "kernelspec": { "display_name": "Python 3", "language": "python", "name": "python3" }, "language_info": { "codemirror_mode": { "name": "ipython", "version": 2 }, "file_extension": ".py", "mimetype": "text/x-python", "name": "python", "nbconvert_exporter": "python", "pygments_lexer": "ipython2", "version": "2.7.6" } }, "nbformat": 4, "nbformat_minor": 5 }