111 commands · 6 cheat sheets · Python

Files, OS, and CLI master quick reference

Browse 111 commands from 6 focused cheat sheets on page 1 of 1. Each example opens its matching detailed section.

Files, OS, and CLI · 22 commands

Python argparse Command-Line Interfaces Cheat Sheet

Use	Syntax	Examples
Create a parser	`parser = argparse.ArgumentParser(prog='tool', description='Process records')`	View examples
Add a positional	`parser.add_argument('input', help='input path')`	View examples
Add an option	`parser.add_argument('-o', '--output', default='-')`	View examples
Parse an explicit list	`args = parser.parse_args(['input.csv', '--output', 'result.json'])`	View examples
Convert a value	`parser.add_argument('--limit', type=int, default=100)`	View examples
Restrict choices	`parser.add_argument('--format', choices=('json', 'csv'))`	View examples
Add positive and negative flags	`parser.add_argument('--cache', action=argparse.BooleanOptionalAction, default=True)`	View examples
Count repeated flags	`parser.add_argument('-v', '--verbose', action='count', default=0)`	View examples
Require one or more values	`parser.add_argument('files', nargs='+')`	View examples
Append repeated option values	`parser.add_argument('--tag', action='append', default=[])`	View examples
Omit an absent attribute	`parser.add_argument('--token', default=argparse.SUPPRESS)`	View examples
Set parser-wide defaults	`parser.set_defaults(timeout=30, handler=run)`	View examples
Create required subcommands	`commands = parser.add_subparsers(dest='command', required=True)`	View examples
Declare a subcommand	`build = commands.add_parser('build', help='build artifacts')`	View examples
Dispatch to a handler	`result = args.handler(args)`	View examples
Validate with a type function	`parser.add_argument('--port', type=parse_port)`	View examples
Make options mutually exclusive	`mode = parser.add_mutually_exclusive_group(required=True)`	View examples
Retain unknown tokens	`args, remaining = parser.parse_known_args(argv)`	View examples
Populate an existing namespace	`args = parser.parse_args(argv, namespace=argparse.Namespace(source='config'))`	View examples
Render plain help	`parser = argparse.ArgumentParser(prog='tool', color=False)`	View examples
Catch conversion errors	`parser = argparse.ArgumentParser(exit_on_error=False)`	View examples
Generate help text	`help_text = parser.format_help()`	View examples

Files, OS, and CLI · 19 commands

Python Configuration with tomllib and configparser Cheat Sheet

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Use	Syntax	Examples
Read a TOML file	`with path.open('rb') as file: config = tomllib.load(file)`	View examples
Read a TOML string	`config = tomllib.loads(source)`	View examples
Support older Python	`tomllib = importlib.import_module('tomllib' if sys.version_info >= (3, 11) else 'tomli')`	View examples
Parse exact decimal values	`config = tomllib.loads(source, parse_float=Decimal)`	View examples
Read TOML date-time values	`released = config['package']['released']`	View examples
Catch invalid TOML	`except tomllib.TOMLDecodeError as error: report(error)`	View examples
Bound untrusted input	`if path.stat().st_size > MAX_CONFIG_BYTES: raise ValueError('configuration too large')`	View examples
Validate a required value	`port = require_port(config['server'].get('port'))`	View examples
Read available INI files	`loaded = parser.read(['defaults.ini', 'local.ini'], encoding='utf-8')`	View examples
Read INI text	`parser.read_string(source)`	View examples
Convert an INI integer	`workers = parser.getint('service', 'workers')`	View examples
Convert an INI boolean	`debug = parser.getboolean('service', 'debug')`	View examples
Provide a missing-option fallback	`timeout = parser.getfloat('service', 'timeout', fallback=5.0)`	View examples
Define shared defaults	`parser['DEFAULT'] = {'timeout': '5', 'retries': '2'}`	View examples
Layer configuration files	`parser.read(['base.ini', 'deployment.ini', 'local.ini'], encoding='utf-8')`	View examples
Disable interpolation	`parser = ConfigParser(interpolation=None)`	View examples
Use cross-section interpolation	`parser = ConfigParser(interpolation=ExtendedInterpolation())`	View examples
Preserve option-name case	`parser.optionxform = str`	View examples
Serialize INI configuration	`parser.write(file, space_around_delimiters=True)`	View examples

Files, OS, and CLI · 19 commands

Python Files and Paths Cheat Sheet

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Use	Syntax	Examples
Create a path object	`config = Path('config/settings.json')`	View examples
Join path segments	`report = base / 'reports' / 'daily.txt'`	View examples
Inspect path components	`path.name, path.stem, path.suffix, path.parent`	View examples
Check existence	`path.exists()`	View examples
Check the path kind	`path.is_file(), path.is_dir()`	View examples
Resolve an absolute path	`absolute = path.resolve()`	View examples
Create parent directories	`output.mkdir(parents=True, exist_ok=True)`	View examples
List directory entries	`for child in directory.iterdir(): print(child.name)`	View examples
Match child paths	`for path in directory.glob('*.json'): print(path)`	View examples
Search recursively	`for path in directory.rglob('*.py'): print(path)`	View examples
Read text	`text = path.read_text(encoding='utf-8')`	View examples
Write text	`path.write_text(text, encoding='utf-8')`	View examples
Process lines lazily	`with path.open(encoding='utf-8') as file: lines = list(file)`	View examples
Read bytes	`data = path.read_bytes()`	View examples
Write bytes	`path.write_bytes(data)`	View examples
Load JSON	`data = json.loads(path.read_text(encoding='utf-8'))`	View examples
Write readable JSON	`path.write_text(json.dumps(data, indent=2) + '\n', encoding='utf-8')`	View examples
Use a temporary directory	`with TemporaryDirectory() as directory: work = Path(directory)`	View examples
Replace a file atomically	`temporary.replace(destination)`	View examples

Files, OS, and CLI · 20 commands

Python OS Signals and Process Environment Cheat Sheet

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Use	Syntax	Examples
Install a handler	`previous = signal.signal(signal.SIGTERM, handle_shutdown)`	View examples
Check the main thread	`is_main = threading.current_thread() is threading.main_thread()`	View examples
List supported signals	`supported = signal.valid_signals()`	View examples
Request graceful stop	`def handler(signum, frame): shutdown.set()`	View examples
Wait interruptibly	`requested = shutdown.wait(timeout=1.0)`	View examples
Restore a disposition	`signal.signal(signal.SIGTERM, previous)`	View examples
Schedule SIGALRM	`remaining = signal.alarm(seconds)`	View examples
Schedule a real-time timer	`previous = signal.setitimer(signal.ITIMER_REAL, delay, interval)`	View examples
Block signals in one thread	`previous = signal.pthread_sigmask(signal.SIG_BLOCK, signals)`	View examples
Read with a default	`mode = os.getenv('APP_MODE', 'production')`	View examples
Require a variable	`database_url = os.environ['DATABASE_URL']`	View examples
Copy the environment	`environment = os.environ.copy()`	View examples
Set a process variable	`os.environ['APP_MODE'] = 'test'`	View examples
Remove a process variable	`os.environ.pop('APP_MODE', None)`	View examples
Reload external changes	`os.reload_environ()`	View examples
Pass a child environment	`subprocess.run(argv, env=child_env, check=True)`	View examples
Override selected child values	`child_env = os.environ \| {'APP_MODE': 'batch'}`	View examples
Expand environment syntax	`expanded = os.path.expandvars(template)`	View examples
Read a bytes environment	`raw = os.environb.get(b'KEY')`	View examples
Check bytes environment support	`available = os.supports_bytes_environ`	View examples

Files, OS, and CLI · 16 commands

Python subprocess and Command Execution Cheat Sheet

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Use	Syntax	Examples
Run an argument sequence	`subprocess.run([program, '--flag', value], check=True)`	View examples
Reuse this Python	`subprocess.run([sys.executable, '-m', 'package'], check=True)`	View examples
Capture both streams	`result = subprocess.run(args, capture_output=True, text=True)`	View examples
Choose text encoding	`subprocess.run(args, capture_output=True, text=True, encoding='utf-8')`	View examples
Merge stderr into stdout	`subprocess.run(args, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True)`	View examples
Require success	`result = subprocess.run(args, check=True)`	View examples
Check after inspection	`result.check_returncode()`	View examples
Read the exit status	`if result.returncode != 0: handle_failure(result.stderr)`	View examples
Bound runtime	`subprocess.run(args, timeout=10, check=True)`	View examples
Handle expiration	`except subprocess.TimeoutExpired as exc: report(exc.cmd, exc.timeout)`	View examples
Send standard input	`subprocess.run(args, input=payload, text=True, check=True)`	View examples
Set child environment	`subprocess.run(args, env={**os.environ, 'APP_MODE': 'test'}, check=True)`	View examples
Set child directory	`subprocess.run(args, cwd=workspace, check=True)`	View examples
Start a managed process	`with subprocess.Popen(args, stdout=subprocess.PIPE, text=True) as process: stdout, _ = process.communicate()`	View examples
Drain process pipes	`stdout, stderr = process.communicate(input=payload, timeout=10)`	View examples
Discard a stream	`subprocess.run(args, stdout=subprocess.DEVNULL, check=True)`	View examples

Files, OS, and CLI · 15 commands

Python zipfile, tarfile, and Compression Cheat Sheet

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Use	Syntax	Examples
Create a ZIP archive	`with ZipFile(path, 'w', compression=ZIP_DEFLATED) as archive: archive.write(source, arcname='data.txt')`	View examples
Write bytes to ZIP	`archive.writestr('manifest.json', payload)`	View examples
Read one ZIP member	`with archive.open('manifest.json') as member: data = member.read(limit + 1)`	View examples
Inspect ZIP metadata	`for info in archive.infolist(): print(info.filename, info.file_size, info.compress_size)`	View examples
Check ZIP CRC values	`bad_member = archive.testzip()`	View examples
Create a compressed tar	`with tarfile.open(path, 'w:gz') as archive: archive.add(source, arcname='data')`	View examples
Detect tar compression	`with tarfile.open(path, 'r:*') as archive: members = archive.getmembers()`	View examples
Add generated bytes to tar	`archive.addfile(info, io.BytesIO(payload))`	View examples
Use the tar data filter	`archive.extractall(destination, filter='data')`	View examples
Validate ZIP destinations	`target = (destination / info.filename).resolve()`	View examples
Compress with gzip	`compressed = gzip.compress(data, compresslevel=6, mtime=0)`	View examples
Compress with bzip2	`compressed = bz2.compress(data, compresslevel=9)`	View examples
Compress with XZ	`compressed = lzma.compress(data, format=lzma.FORMAT_XZ)`	View examples
Incremental zlib compression	`compressor = zlib.compressobj(level=6)`	View examples
Create an archive by format	`archive_path = shutil.make_archive(base_name, 'zip', root_dir=source_dir)`	View examples

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