888 commands · 53 cheat sheets · 7 subcategories

Python master quick reference — Page 4

Browse 197 commands from 12 focused cheat sheets on page 4 of 5. Each example opens its matching detailed section.

Files, OS, and CLI · 16 commands

Python subprocess and Command Execution Cheat Sheet

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

Packages, Testing, and Quality · 15 commands

Python importlib, Metadata, Resources, and Plugins Cheat Sheet

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Use	Syntax	Examples
Import by name	`module = importlib.import_module('package.module')`	View examples
Resolve a relative import	`module = importlib.import_module('.codec', package='app.plugins')`	View examples
Find a module specification	`spec = importlib.util.find_spec('package.module')`	View examples
Invalidate finder caches	`importlib.invalidate_caches()`	View examples
Read a distribution version	`release = importlib.metadata.version('distribution-name')`	View examples
Read core metadata	`details = importlib.metadata.metadata('distribution-name')`	View examples
Read declared requirements	`requirements = importlib.metadata.requires('distribution-name') or []`	View examples
Map import to distributions	`owners = importlib.metadata.packages_distributions().get('import_name', [])`	View examples
Get a resource root	`root = importlib.resources.files('package_name')`	View examples
Read a text resource	`text = root.joinpath('data/defaults.ini').read_text(encoding='utf-8')`	View examples
Materialize a resource path	`with importlib.resources.as_file(resource) as path: consume(path)`	View examples
Discover a plugin group	`plugins = importlib.metadata.entry_points(group='acme.plugins')`	View examples
Select one entry point	`matches = plugins.select(name='formatter')`	View examples
Load a plugin object	`plugin = entry_point.load()`	View examples
Handle missing distribution metadata	`except importlib.metadata.PackageNotFoundError: use_fallback()`	View examples

Packages, Testing, and Quality · 17 commands

Python Logging and Observability Cheat Sheet

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Use	Syntax	Examples
Create a module logger	`logger = logging.getLogger(__name__)`	View examples
Set a logger threshold	`logger.setLevel(logging.INFO)`	View examples
Defer message formatting	`logger.info('processed %d records', count)`	View examples
Guard expensive diagnostics	`if logger.isEnabledFor(logging.DEBUG): logger.debug('state=%r', build_state())`	View examples
Configure a small application	`logging.basicConfig(level=logging.INFO, format='%(levelname)s:%(name)s:%(message)s')`	View examples
Apply dictionary configuration	`logging.config.dictConfig({'version': 1, 'handlers': handlers, 'root': root})`	View examples
Preserve existing loggers	`config = {'version': 1, 'disable_existing_loggers': False, 'root': root}`	View examples
Add a stream destination	`handler = logging.StreamHandler(sys.stdout)`	View examples
Set a destination threshold	`handler.setLevel(logging.ERROR)`	View examples
Stop duplicate propagation	`logger.propagate = False`	View examples
Attach event context	`logger.info('checkout accepted', extra={'order_id': order_id})`	View examples
Reuse stable context	`request_log = logging.LoggerAdapter(logger, {'request_id': request_id})`	View examples
Record the active exception	`except OSError: logger.exception('configuration load failed')`	View examples
Include exception information	`logger.error('operation failed', exc_info=True)`	View examples
Attribute a helper's caller	`logger.warning('deprecated call', stacklevel=2)`	View examples
Filter one destination	`handler.addFilter(lambda record: record.name != 'app.health')`	View examples
Emit structured records	`handler.setFormatter(JsonFormatter())`	View examples

Packages, Testing, and Quality · 12 commands

Python Modules and Packages Cheat Sheet

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Use	Syntax	Examples
Import a module	`import statistics`	View examples
Import a name	`from pathlib import Path`	View examples
Alias an import	`import collections.abc as cabc`	View examples
Guard script entry	`if __name__ == '__main__': main()`	View examples
Run by module name	`python -m package.module`	View examples
Regular package marker	`package/__init__.py`	View examples
Relative import	`from .formatting import render`	View examples
Declare star-import names	`__all__ = ['Client', 'connect']`	View examples
Inspect module identity	`print(module.__name__)`	View examples
Inspect source location	`print(module.__file__)`	View examples
Find without importing	`spec = importlib.util.find_spec('package.module')`	View examples
Read package data	`text = resources.files('package').joinpath('defaults.json').read_text()`	View examples

Packages, Testing, and Quality · 19 commands

Python Packaging, Virtual Environments, and pyproject.toml Cheat Sheet

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Use	Syntax	Examples
Create a virtual environment	`python -m venv .venv`	View examples
Seed current packaging tools	`python -m venv --upgrade-deps .venv`	View examples
Invoke the environment directly	`.venv/bin/python -m pip --version`	View examples
Declare backend requirements	`requires = ['hatchling>=1.26'] # in [build-system]`	View examples
Select a build backend	`build-backend = 'hatchling.build'`	View examples
Declare Python compatibility	`requires-python = '>=3.11'`	View examples
Declare a runtime dependency	`dependencies = ['httpx>=0.27,<1']`	View examples
Publish a console command	`acme = 'acme.cli:main' # in [project.scripts]`	View examples
Declare an optional feature	`test = ['pytest>=8'] # in [project.optional-dependencies]`	View examples
Apply deployment constraints	`python -m pip install -c constraints.txt -r requirements.txt`	View examples
Require artifact hashes	`python -m pip install --require-hashes -r requirements.txt`	View examples
Use a src package layout	`src/acme/__init__.py`	View examples
Open packaged text	`text = resources.files('acme').joinpath('data.txt').read_text(encoding='utf-8')`	View examples
Build sdist and wheel	`python -m build`	View examples
Build only a wheel	`python -m build --wheel`	View examples
Install the built wheel	`python -m pip install --force-reinstall dist/acme_tools-1.2.0-py3-none-any.whl`	View examples
Validate distribution metadata	`python -m twine check dist/*`	View examples
Upload to TestPyPI	`python -m twine upload --repository testpypi dist/*`	View examples
Read installed metadata	`version = importlib.metadata.version('acme-tools')`	View examples

Packages, Testing, and Quality · 14 commands

Python unittest and Mocking Cheat Sheet

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Use	Syntax	Examples
Create a test case	`class ParserTests(unittest.TestCase): ...`	View examples
Declare a test	`def test_rejects_empty_input(self): ...`	View examples
Compare values	`self.assertEqual(actual, expected)`	View examples
Assert an exception	`with self.assertRaises(ValueError): parse('')`	View examples
Assert message text	`with self.assertRaisesRegex(ValueError, 'positive'): validate(0)`	View examples
Prepare each test	`def setUp(self): self.client = Client()`	View examples
Register cleanup	`self.addCleanup(resource.close)`	View examples
Name table cases	`with self.subTest(value=value): self.assertTrue(valid(value))`	View examples
Create a specified mock	`client = Mock(spec=ApiClient)`	View examples
Patch with signature checks	`@patch('module.ApiClient', autospec=True)`	View examples
Configure a return	`client.fetch.return_value = {'status': 'ok'}`	View examples
Raise or vary calls	`client.fetch.side_effect = TimeoutError('slow')`	View examples
Verify one call	`client.fetch.assert_called_once_with('/status')`	View examples
Use a temporary directory	`with tempfile.TemporaryDirectory() as directory: ...`	View examples

Concurrency, Networking, and Performance · 12 commands

Python asyncio and await Cheat Sheet

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Use	Syntax	Examples
Define a coroutine	`async def fetch(): return await client.get('/')`	View examples
Run an entry coroutine	`asyncio.run(main())`	View examples
Await completion	`result = await operation()`	View examples
Schedule a task	`task = asyncio.create_task(operation())`	View examples
Group child tasks	`async with asyncio.TaskGroup() as group: group.create_task(operation())`	View examples
Collect ordered results	`results = await asyncio.gather(*coroutines)`	View examples
Bound a block by time	`async with asyncio.timeout(5): result = await operation()`	View examples
Request cancellation	`task.cancel()`	View examples
Yield to the loop	`await asyncio.sleep(0)`	View examples
Create a bounded queue	`queue = asyncio.Queue(maxsize=100)`	View examples
Bound concurrent access	`async with asyncio.Semaphore(10): await operation()`	View examples
Run blocking I/O in a thread	`result = await asyncio.to_thread(blocking_function, argument)`	View examples

Concurrency, Networking, and Performance · 16 commands

Python concurrent.futures and Parallel Work Cheat Sheet

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Use	Syntax	Examples
Create a thread pool	`with ThreadPoolExecutor(max_workers=8) as executor: results = list(executor.map(fetch, urls))`	View examples
Create a process pool	`with ProcessPoolExecutor(max_workers=4) as executor: results = list(executor.map(cpu_task, values))`	View examples
Create an interpreter pool	`with InterpreterPoolExecutor(max_workers=4) as executor: results = list(executor.map(cpu_task, values))`	View examples
Submit one call	`future = executor.submit(function, argument)`	View examples
Retrieve a result	`value = future.result(timeout=5)`	View examples
Add a completion callback	`future.add_done_callback(record_completion)`	View examples
Map in input order	`results = executor.map(function, items)`	View examples
Bound submitted map work	`results = executor.map(function, items, buffersize=16)`	View examples
Batch process-pool items	`results = executor.map(function, items, chunksize=64)`	View examples
Consume completed futures	`results = [future.result() for future in as_completed(futures)]`	View examples
Wait for a condition	`done, pending = wait(futures, timeout=5, return_when=FIRST_EXCEPTION)`	View examples
Limit a result wait	`future.result(timeout=2)`	View examples
Cancel pending work	`cancelled = future.cancel()`	View examples
Shut down an executor	`executor.shutdown(wait=True, cancel_futures=True)`	View examples
Guard process entry	`if __name__ == '__main__': main()`	View examples
Choose a process context	`ProcessPoolExecutor(mp_context=multiprocessing.get_context('spawn'))`	View examples

Concurrency, Networking, and Performance · 20 commands

Python Hashing, HMAC, and Secrets Cheat Sheet

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Use	Syntax	Examples
Hash bytes with SHA-256	`digest = hashlib.sha256(data).digest()`	View examples
Render a hexadecimal digest	`text = hashlib.sha256(data).hexdigest()`	View examples
Hash data incrementally	`hasher.update(chunk)`	View examples
Hash an open binary file	`with path.open('rb') as file: digest = hashlib.file_digest(file, 'sha256')`	View examples
Branch a partial hash	`branch = hasher.copy()`	View examples
Construct an algorithm by name	`hasher = hashlib.new('sha256', data)`	View examples
Inspect portable algorithms	`portable = hashlib.algorithms_guaranteed`	View examples
Build an HMAC incrementally	`mac = hmac.new(key, message, digestmod=hashlib.sha256)`	View examples
Calculate an HMAC in one call	`tag = hmac.digest(key, message, 'sha256')`	View examples
Compare authenticators safely	`valid = hmac.compare_digest(received_tag, expected_tag)`	View examples
Generate random secret bytes	`key = secrets.token_bytes(32)`	View examples
Generate a hexadecimal token	`token = secrets.token_hex(32)`	View examples
Generate a URL-safe token	`token = secrets.token_urlsafe(32)`	View examples
Choose securely from a sequence	`character = secrets.choice(alphabet)`	View examples
Generate a bounded integer	`index = secrets.randbelow(exclusive_upper_bound)`	View examples
Derive a PBKDF2 verifier	`derived = hashlib.pbkdf2_hmac('sha256', password, salt, iterations, dklen=32)`	View examples
Derive a scrypt verifier	`derived = hashlib.scrypt(password, salt=salt, n=16384, r=8, p=1, dklen=32)`	View examples
Create a unique password salt	`salt = secrets.token_bytes(16)`	View examples
Authenticate with keyed BLAKE2	`tag = hashlib.blake2b(message, key=key, digest_size=32).digest()`	View examples
Separate BLAKE2 domains	`digest = hashlib.blake2b(data, person=b'cache-v1', digest_size=16).digest()`	View examples

Concurrency, Networking, and Performance · 15 commands

Python Memory, Garbage Collection, and Weak References Cheat Sheet

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Use	Syntax	Examples
Measure shallow size	`shallow_bytes = sys.getsizeof(value)`	View examples
Inspect CPython references	`count_with_temporary = sys.getrefcount(value)`	View examples
Run cyclic collection	`unreachable = gc.collect()`	View examples
Check collector state	`collector_enabled = gc.isenabled()`	View examples
Read GC thresholds	`thresholds = gc.get_threshold()`	View examples
Freeze tracked objects	`gc.freeze()`	View examples
Create a weak reference	`reference = weakref.ref(instance)`	View examples
Cache values weakly	`cache = weakref.WeakValueDictionary()`	View examples
Associate metadata weakly	`metadata = weakref.WeakKeyDictionary()`	View examples
Track instances weakly	`instances = weakref.WeakSet()`	View examples
Register a finalizer	`cleanup = weakref.finalize(owner, close_resource, resource_id)`	View examples
Start allocation tracing	`tracemalloc.start(10)`	View examples
Capture a snapshot	`snapshot = tracemalloc.take_snapshot()`	View examples
Compare snapshots	`changes = after.compare_to(before, 'lineno')`	View examples
Read traced current and peak	`current, peak = tracemalloc.get_traced_memory()`	View examples

Concurrency, Networking, and Performance · 26 commands

Python multiprocessing and Shared Memory Cheat Sheet

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Use	Syntax	Examples
List available start methods	`methods = multiprocessing.get_all_start_methods()`	View examples
Create an explicit context	`ctx = multiprocessing.get_context('spawn')`	View examples
Set the global start method	`multiprocessing.set_start_method('spawn')`	View examples
Guard application startup	`if __name__ == '__main__': main()`	View examples
Start one process	`process = ctx.Process(target=worker, args=(input_value,)); process.start()`	View examples
Wait for process completion	`process.join(timeout=5)`	View examples
Release a Process handle	`process.close()`	View examples
Map work through a pool	`with ctx.Pool(processes=4) as pool: results = pool.map(transform, items, chunksize=32)`	View examples
Submit an asynchronous pool call	`pending = pool.apply_async(transform, (item,)); result = pending.get(timeout=5)`	View examples
Drain and close a pool	`pool.close(); pool.join()`	View examples
Send a queued message	`queue.put(message); received = queue.get(timeout=5)`	View examples
Create a one-way pipe	`receiver, sender = ctx.Pipe(duplex=False)`	View examples
Wait for ready connections	`ready = multiprocessing.connection.wait(connections, timeout=5)`	View examples
Signal workers with an Event	`ready.set(); ready.wait(timeout=5)`	View examples
Protect a critical section	`with lock: shared_value.value += 1`	View examples
Create a synchronized scalar	`counter = ctx.Value('i', 0)`	View examples
Create a shared-memory block	`block = SharedMemory(create=True, size=byte_count)`	View examples
Attach by shared-memory name	`block = SharedMemory(name=block_name)`	View examples
Close and unlink shared memory	`block.close(); block.unlink()`	View examples
Opt out of resource tracking	`block = SharedMemory(name=block_name, track=False)`	View examples
Run a manager server	`with ctx.Manager() as manager: shared = manager.dict()`	View examples
Create a managed list	`shared_items = manager.list(initial_items)`	View examples
Receive only trusted objects	`message = connection.recv()`	View examples
Use an importable worker	`def worker(payload): return process_payload(payload)`	View examples
Request cooperative shutdown	`stop_event.set(); process.join(timeout=5)`	View examples
Terminate an unresponsive process	`if process.is_alive(): process.terminate(); process.join()`	View examples

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