888 commands · 53 cheat sheets · 7 subcategories

Python master quick reference — Page 3

Browse 206 commands from 12 focused cheat sheets on page 3 of 5. Each example opens its matching detailed section.

Data and Serialization · 13 commands

Python Regular Expressions Cheat Sheet

Use	Syntax	Examples
Compile a pattern	`pattern = re.compile(r'\d{4}-\d{2}-\d{2}')`	View examples
Search anywhere	`match = pattern.search(text)`	View examples
Match from start	`match = pattern.match(text)`	View examples
Validate the whole string	`match = pattern.fullmatch(text)`	View examples
Capture a group	`value = match.group(1)`	View examples
Named capture	`r'(?P<year>\d{4})-(?P<month>\d{2})'`	View examples
Non-capturing group	`r'(?:https?\|ftp)://'`	View examples
Iterate matches	`for match in pattern.finditer(text): print(match.span())`	View examples
Collect matches	`values = pattern.findall(text)`	View examples
Split by pattern	`parts = re.split(r'\s,\s', text)`	View examples
Replace matches	`clean = re.sub(r'\s+', ' ', text).strip()`	View examples
Verbose pattern	`pattern = re.compile(r'''...''', re.VERBOSE)`	View examples
Ignore case	`pattern = re.compile(r'error', re.IGNORECASE)`	View examples

Data and Serialization · 17 commands

Python Text Encoding and Unicode Cheat Sheet

Open full cheat sheet

Use	Syntax	Examples
Encode UTF-8	`payload = text.encode('utf-8')`	View examples
Decode UTF-8	`text = payload.decode('utf-8')`	View examples
Use strict decoding	`text = payload.decode('utf-8', errors='strict')`	View examples
Open UTF-8 text	`with open(path, 'r', encoding='utf-8') as stream: text = stream.read()`	View examples
Write stable LF newlines	`with open(path, 'w', encoding='utf-8', newline='\n') as stream: stream.write(text)`	View examples
Wrap a binary stream	`text_stream = io.TextIOWrapper(binary_stream, encoding='utf-8', newline='')`	View examples
Normalize canonical composition	`normalized = unicodedata.normalize('NFC', text)`	View examples
Check normalization	`ok = unicodedata.is_normalized('NFC', text)`	View examples
Build a caseless key	`key = unicodedata.normalize('NFC', text).casefold()`	View examples
Lowercase for presentation	`lowered = text.lower()`	View examples
Read a code point	`number = ord(character)`	View examples
Create a character	`character = chr(number)`	View examples
Read a Unicode name	`name = unicodedata.name(character, 'UNNAMED')`	View examples
Replace malformed input	`text = payload.decode('utf-8', errors='replace')`	View examples
Preserve OS bytes	`text = payload.decode(filesystem_encoding, errors='surrogateescape')`	View examples
Create a streaming decoder	`decoder = codecs.getincrementaldecoder('utf-8')(errors='strict')`	View examples
Finish a decode stream	`tail = decoder.decode(b'', final=True)`	View examples

Data and Serialization · 20 commands

Python XML Parsing and Generation Cheat Sheet

Open full cheat sheet

Use	Syntax	Examples
Parse an XML value	`root = ET.fromstring(xml_bytes)`	View examples
Parse an XML file	`tree = ET.parse(path)`	View examples
Catch malformed XML	`except ET.ParseError as error: report(error.position)`	View examples
Create an expanded name	`tag = '{urn:books}title'`	View examples
Query with a prefix map	`items = root.findall('b:item', {'b': 'urn:books'})`	View examples
Choose a serialization prefix	`ET.register_namespace('b', 'urn:books')`	View examples
Find one matching element	`item = root.find('./item[@id="a"]')`	View examples
Find matching elements	`items = root.findall('.//item')`	View examples
Iterate matching descendants	`for item in root.iter('item'): consume(item)`	View examples
Append a child element	`child = ET.SubElement(parent, 'item', {'id': item_id})`	View examples
Set element text	`child.text = value`	View examples
Remove a child	`parent.remove(child)`	View examples
Serialize to text	`xml_text = ET.tostring(root, encoding='unicode')`	View examples
Write UTF-8 XML	`tree.write(path, encoding='utf-8', xml_declaration=True)`	View examples
Canonicalize XML	`canonical = ET.canonicalize(xml_data=xml_text)`	View examples
Iterate completed elements	`events = ET.iterparse(source, events=('end',))`	View examples
Release processed content	`element.clear()`	View examples
Create a pull parser	`parser = ET.XMLPullParser(events=('start', 'end'))`	View examples
Inspect the Expat version	`version = pyexpat.EXPAT_VERSION`	View examples
Bound XML input bytes	`if len(xml_bytes) > MAX_XML_BYTES: raise ValueError('XML too large')`	View examples

Pandas Data Analysis · 15 commands

Pandas Data Cleaning and Missing Data Cheat Sheet

Open full cheat sheet

Use	Syntax	Examples
Count missing values	`missing = df.isna().sum()`	View examples
Select complete rows	`complete = df.loc[df[['id', 'email']].notna().all(axis='columns')]`	View examples
Drop incomplete records	`clean = df.dropna(subset=['customer_id', 'ordered_at'])`	View examples
Fill column defaults	`clean = df.fillna({'country': 'unknown', 'quantity': 0})`	View examples
Forward-fill briefly	`df['status'] = df['status'].ffill(limit=1)`	View examples
Interpolate numeric gaps	`df['reading'] = df['reading'].interpolate(limit_area='inside')`	View examples
Replace sentinels	`df['status'] = df['status'].replace({'N/A': pd.NA, '': pd.NA})`	View examples
Normalize text	`df['email'] = df['email'].str.strip().str.lower()`	View examples
Normalize categories	`df['status'] = df['status'].replace({'in progress': 'active', 'open': 'active'})`	View examples
Parse numeric values	`df['amount'] = pd.to_numeric(df['amount'], errors='coerce')`	View examples
Parse exact dates	`df['ordered_at'] = pd.to_datetime(df['ordered_at'], format='%Y-%m-%d', errors='coerce')`	View examples
Use nullable dtypes	`df = df.convert_dtypes()`	View examples
Find values out of range	`invalid = df.loc[df['quantity'].notna() & ~df['quantity'].between(1, 100)]`	View examples
Find duplicate keys	`duplicates = df.loc[df.duplicated('order_id', keep=False)]`	View examples
Keep the latest record	`latest = df.sort_values('updated_at').drop_duplicates('order_id', keep='last')`	View examples

Pandas Data Analysis · 16 commands

Pandas DataFrames and Indexing Cheat Sheet

Open full cheat sheet

Use	Syntax	Examples
Create a DataFrame	`df = pd.DataFrame({'name': ['Ada', 'Lin'], 'score': [91, 84]})`	View examples
Read CSV data	`df = pd.read_csv('scores.csv', usecols=['name', 'score'])`	View examples
Preview rows	`preview = df.head(3)`	View examples
Inspect column types	`types = df.dtypes`	View examples
Select one column	`scores = df['score']`	View examples
Select by labels	`result = df.loc[df.index[:2], ['name', 'score']]`	View examples
Select by position	`result = df.iloc[:2, [0, 2]]`	View examples
Filter with a mask	`high_scores = df.loc[df['score'].ge(90)]`	View examples
Match allowed values	`selected = df.loc[df['team'].isin({'red', 'blue'})]`	View examples
Query rows	`selected = df.query('score >= @minimum and active')`	View examples
Update matching rows	`df.loc[df['score'].ge(90), 'level'] = 'advanced'`	View examples
Create a derived column	`result = df.assign(percent=lambda frame: frame['score'] / frame['possible'] * 100)`	View examples
Rename columns	`result = df.rename(columns={'score': 'points'})`	View examples
Sort rows	`result = df.sort_values(['team', 'score'], ascending=[True, False])`	View examples
Set an index	`indexed = df.set_index('student_id', verify_integrity=True)`	View examples
Restore a column index	`flat = indexed.reset_index()`	View examples

Pandas Data Analysis · 15 commands

Pandas GroupBy, Aggregation, and Reshaping Cheat Sheet

Open full cheat sheet

Use	Syntax	Examples
Sum by group	`totals = df.groupby('region')['revenue'].sum()`	View examples
Keep group columns	`totals = df.groupby('region', as_index=False)['revenue'].sum()`	View examples
Group by several keys	`totals = df.groupby(['region', 'product'], as_index=False)['revenue'].sum()`	View examples
Name aggregate columns	`summary = df.groupby('region').agg(total=('revenue', 'sum'), average=('revenue', 'mean'))`	View examples
Count group rows	`counts = df.groupby('region').size()`	View examples
Count present values	`counts = df.groupby('region')['revenue'].count()`	View examples
Broadcast group totals	`df['region_total'] = df.groupby('region')['revenue'].transform('sum')`	View examples
Calculate group share	`df['share'] = df['revenue'] / df.groupby('region')['revenue'].transform('sum')`	View examples
Calculate grouped running totals	`df['running'] = df.groupby('account')['amount'].cumsum()`	View examples
Keep qualifying groups	`result = df.groupby('region').filter(lambda group: len(group) >= 2)`	View examples
Pivot unique coordinates	`wide = df.pivot(index='date', columns='metric', values='value')`	View examples
Aggregate a pivot table	`wide = df.pivot_table(index='region', columns='product', values='revenue', aggfunc='sum', fill_value=0)`	View examples
Unpivot wide columns	`long = df.melt(id_vars='id', var_name='metric', value_name='value')`	View examples
Explode list values	`long = df.explode('tags', ignore_index=True)`	View examples
Build a cross-tabulation	`counts = pd.crosstab(df['region'], df['status'], margins=True)`	View examples

Pandas Data Analysis · 14 commands

Pandas Merging, Joining, and Concatenation Cheat Sheet

Open full cheat sheet

Use	Syntax	Examples
Keep matching keys	`result = orders.merge(customers, on='customer_id', how='inner')`	View examples
Preserve left rows	`result = orders.merge(customers, on='customer_id', how='left')`	View examples
Join different key names	`result = orders.merge(customers, left_on='customer_id', right_on='id', how='left')`	View examples
Validate key cardinality	`result = orders.merge(customers, on='customer_id', validate='many_to_one')`	View examples
Track row provenance	`audit = left.merge(right, on='id', how='outer', indicator=True)`	View examples
Label overlapping columns	`result = current.merge(previous, on='id', suffixes=('_current', '_previous'))`	View examples
Stack row batches	`combined = pd.concat([january, february], ignore_index=True)`	View examples
Require identical columns	`combined = pd.concat(frames, join='inner', ignore_index=True)`	View examples
Align columns by index	`combined = pd.concat([features, targets], axis='columns')`	View examples
Preserve batch identity	`combined = pd.concat({'jan': january, 'feb': february}, names=['month'])`	View examples
Join on indexes	`result = customers.join(accounts, how='left', validate='one_to_one')`	View examples
Fill from a fallback	`combined = primary.combine_first(fallback)`	View examples
Match the nearest prior key	`result = pd.merge_asof(events, rates, on='time', direction='backward')`	View examples
Show changed values	`changes = before.compare(after, result_names=('before', 'after'))`	View examples

Pandas Data Analysis · 16 commands

Pandas Time Series, Resampling, and Rolling Cheat Sheet

Open full cheat sheet

Use	Syntax	Examples
Parse exact timestamps	`df['time'] = pd.to_datetime(df['time'], format='%Y-%m-%d %H:%M', errors='raise')`	View examples
Normalize to UTC	`df['time'] = pd.to_datetime(df['time'], utc=True, errors='coerce')`	View examples
Create a regular index	`index = pd.date_range('2026-08-01', periods=24, freq='h', tz='UTC')`	View examples
Set a sorted time index	`series = df.set_index('time').sort_index()`	View examples
Extract time components	`df['weekday'] = df['time'].dt.day_name()`	View examples
Localize wall times	`localized = naive.dt.tz_localize('America/Sao_Paulo', ambiguous='raise', nonexistent='raise')`	View examples
Convert time zones	`local = utc.dt.tz_convert('America/Sao_Paulo')`	View examples
Aggregate daily totals	`daily = series.resample('D').sum(min_count=1)`	View examples
Control interval edges	`daily = series.resample('D', closed='right', label='right').sum()`	View examples
Expose missing intervals	`hourly = series.asfreq('h')`	View examples
Interpolate by time	`hourly = series.resample('h').asfreq().interpolate(method='time', limit_area='inside')`	View examples
Calculate a rolling mean	`result = series.rolling('3h', min_periods=2).mean()`	View examples
Calculate an expanding total	`result = series.expanding(min_periods=1).sum()`	View examples
Calculate an EWM mean	`result = series.ewm(span=3, adjust=False).mean()`	View examples
Create a one-period lag	`df['previous'] = df['value'].shift(1)`	View examples
Calculate fractional change	`df['change'] = df['value'].pct_change(fill_method=None)`	View examples

Files, OS, and CLI · 22 commands

Python argparse Command-Line Interfaces Cheat Sheet

Open full 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

Open full cheat sheet

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

Open full cheat sheet

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

Open full cheat sheet

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

Back to Python cheat sheets