176 commands · 10 cheat sheets · Python

Concurrency, Networking, and Performance master quick reference

Browse 176 commands from 10 focused cheat sheets on page 1 of 1. Each example opens its matching detailed section.

Concurrency, Networking, and Performance · 12 commands

Python asyncio and await Cheat Sheet

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

Concurrency, Networking, and Performance · 19 commands

Python Profiling, Benchmarking, and Tracing Cheat Sheet

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Use	Syntax	Examples
Read a monotonic performance clock	`started = time.perf_counter()`	View examples
Read integer nanoseconds	`started_ns = time.perf_counter_ns()`	View examples
Record interpreter identity	`identity = (sys.implementation.name, platform.python_version())`	View examples
Time a callable	`seconds = timeit.timeit(callable_under_test, number=1000)`	View examples
Collect repeated timings	`samples = timeit.repeat(stmt, setup=setup, repeat=7, number=1000)`	View examples
Run the timeit CLI	`python -m timeit -s 'data = list(range(100))' 'sum(data)'`	View examples
Profile a callable	`profile.runcall(main)`	View examples
Profile a module to a file	`python -m cProfile -o profile.pstats -m package.module`	View examples
Sort by cumulative time	`stats.sort_stats(pstats.SortKey.CUMULATIVE).print_stats(20)`	View examples
Start allocation tracing	`tracemalloc.start(10)`	View examples
Capture allocations	`snapshot = tracemalloc.take_snapshot()`	View examples
Compare snapshots	`diff = after.compare_to(before, 'lineno')`	View examples
Install a trace hook	`previous = sys.gettrace(); sys.settrace(trace_function)`	View examples
Restore a trace hook	`sys.settrace(previous)`	View examples
Trace threading workers	`threading.settrace(trace_function)`	View examples
Enable fault tracebacks	`faulthandler.enable()`	View examples
Inspect current thread frames	`frames = sys._current_frames()`	View examples
Summarize the median	`middle = statistics.median(samples)`	View examples
Compute quartile cut points	`quartiles = statistics.quantiles(samples, n=4, method='inclusive')`	View examples

Concurrency, Networking, and Performance · 18 commands

Python Sockets and Selectors Cheat Sheet

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Use	Syntax	Examples
Resolve stream candidates	`addresses = socket.getaddrinfo(host, port, type=socket.SOCK_STREAM)`	View examples
Open a TCP connection	`sock = socket.create_connection((host, port), timeout=5.0)`	View examples
Close a socket reliably	`with socket.socket() as sock: use(sock)`	View examples
Send the full buffer	`sock.sendall(payload)`	View examples
Detect stream EOF	`chunk = sock.recv(65536)`	View examples
Encode a network-order length	`header = struct.pack('!I', len(payload))`	View examples
Bind an ephemeral loopback port	`listener.bind(('127.0.0.1', 0))`	View examples
Start listening	`listener.listen(128)`	View examples
Accept one connection	`connection, address = listener.accept()`	View examples
Set an operation timeout	`sock.settimeout(2.0)`	View examples
Enable non-blocking mode	`sock.setblocking(False)`	View examples
Register read interest	`selector.register(sock, selectors.EVENT_READ, data=state)`	View examples
Wait for readiness	`events = selector.select(timeout=1.0)`	View examples
Change event interest	`selector.modify(sock, selectors.EVENT_READ \| selectors.EVENT_WRITE, state)`	View examples
Send a UDP datagram	`sent = sock.sendto(payload, destination)`	View examples
Receive a UDP datagram	`payload, peer = sock.recvfrom(65507)`	View examples
Half-close the write side	`sock.shutdown(socket.SHUT_WR)`	View examples
Create safe client TLS defaults	`context = ssl.create_default_context()`	View examples

Concurrency, Networking, and Performance · 16 commands

Python sqlite3 Databases Cheat Sheet

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Use	Syntax	Examples
Open an in-memory database	`con = sqlite3.connect(':memory:')`	View examples
Open a database file	`con = sqlite3.connect('app.db', timeout=5.0)`	View examples
Create a table safely	`con.execute('CREATE TABLE IF NOT EXISTS task(id INTEGER PRIMARY KEY, title TEXT NOT NULL)')`	View examples
Bind positional values	`con.execute('SELECT * FROM task WHERE id = ?', (task_id,))`	View examples
Bind named values	`con.execute('UPDATE task SET done = :done WHERE id = :id', {'done': 1, 'id': task_id})`	View examples
Insert a batch	`con.executemany('INSERT INTO task(title) VALUES(?)', [(title,) for title in titles])`	View examples
Commit or roll back a unit	`with con: con.execute('UPDATE account SET balance = balance - ? WHERE id = ?', (amount, account_id))`	View examples
Select PEP 249 control	`con = sqlite3.connect('app.db', autocommit=False)`	View examples
Inspect transaction state	`if con.in_transaction: con.rollback()`	View examples
Enforce foreign keys	`con.execute('PRAGMA foreign_keys = ON')`	View examples
Handle constraint failures	`except sqlite3.IntegrityError as error: con.rollback()`	View examples
Read columns by name	`con.row_factory = sqlite3.Row`	View examples
Fetch one result	`row = con.execute('SELECT title FROM task WHERE id = ?', (task_id,)).fetchone()`	View examples
Create a nested recovery point	`con.execute('SAVEPOINT before_optional_work')`	View examples
Undo to a savepoint	`con.execute('ROLLBACK TO SAVEPOINT before_optional_work')`	View examples
Copy a live database	`source.backup(destination, pages=100)`	View examples

Concurrency, Networking, and Performance · 19 commands

Python Threading and Synchronization Cheat Sheet

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Use	Syntax	Examples
Start a thread	`worker.start()`	View examples
Wait with a deadline	`worker.join(timeout=2.0)`	View examples
Name a worker	`worker = threading.Thread(name='indexer', target=build_index)`	View examples
Guard a critical section	`with lock: update_shared_state()`	View examples
Attempt bounded acquisition	`acquired = lock.acquire(timeout=0.5)`	View examples
Create a reentrant lock	`lock = threading.RLock()`	View examples
Wait for a predicate	`ready = condition.wait_for(predicate, timeout=1.0)`	View examples
Notify one waiter	`condition.notify()`	View examples
Request cooperative stop	`stop_event.set()`	View examples
Limit concurrent entries	`limit = threading.Semaphore(4)`	View examples
Detect excess release	`limit = threading.BoundedSemaphore(value=4)`	View examples
Create a phase barrier	`barrier = threading.Barrier(parties=3, timeout=5.0)`	View examples
Arrive at a barrier	`index = barrier.wait()`	View examples
Abort a barrier	`barrier.abort()`	View examples
Create backpressure	`jobs = queue.Queue(maxsize=100)`	View examples
Acknowledge a queued task	`jobs.task_done()`	View examples
Wait for task acknowledgements	`jobs.join()`	View examples
Check completion after join	`if worker.is_alive(): handle_timeout()`	View examples
Install an exception observer	`threading.excepthook = report_thread_failure`	View examples

Concurrency, Networking, and Performance · 15 commands

Python urllib HTTP Clients Cheat Sheet

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Use	Syntax	Examples
Open a URL	`with urlopen(request, timeout=10) as response: body = response.read(1_000_001)`	View examples
Build a request	`request = Request(url, headers={'Accept': 'application/json'}, method='GET')`	View examples
Inspect a response	`status, final_url = response.status, response.geturl()`	View examples
Decode a response body	`text = body.decode(response.headers.get_content_charset() or 'utf-8')`	View examples
Encode a query string	`query = urlencode({'q': 'red fox', 'page': 2})`	View examples
Encode repeated parameters	`query = urlencode({'tag': ['python', 'web']}, doseq=True)`	View examples
Build a form POST	`request = Request(url, data=urlencode(fields).encode('ascii'), method='POST')`	View examples
Split a URL	`parts = urlsplit(candidate)`	View examples
Quote a path segment	`segment = quote(user_value, safe='')`	View examples
Resolve a relative URL	`next_url = urljoin(base_url, relative_url)`	View examples
Catch HTTP status errors	`except HTTPError as error: status = error.code`	View examples
Catch transport errors	`except URLError as error: reason = error.reason`	View examples
Create verified TLS settings	`context = ssl.create_default_context()`	View examples
Disable inherited proxies	`opener = build_opener(ProxyHandler({}))`	View examples
Keep a header off redirects	`request.add_unredirected_header('Authorization', token)`	View examples

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