python

class MyClass:
    def __init__(self):
        # Public attribute
        self.public_var: str = "visible"
        
        # Protected attribute (convention only)
        self._protected_var: str = "use with care"
        
        # Private attribute (name mangled to _MyClass__secret)
        self.__secret: str = "truly private"

# Good
from absl import flags
from doctor.who import jodie

# Bad
import jodie  # Ambiguous

def fetch_smalltable_rows(
    table_handle: smalltable.Table,
    keys: Sequence[bytes | str],
    require_all_keys: bool = False,
) -> Mapping[bytes, tuple[str, ...]]:
    """Fetches rows from a Smalltable.

    Retrieves rows pertaining to the given keys from the Table instance
    represented by table_handle. String keys will be UTF-8 encoded.

    Args:
        table_handle: An open smalltable.Table instance.
        keys: A sequence of strings representing the key of each table
            row to fetch. String keys will be UTF-8 encoded.
        require_all_keys: If True only rows with values set for all keys will be
            returned.

    Returns:
        A dict mapping keys to the corresponding table row data
        fetched. Each row is represented as a tuple of strings. For
        example:

        {b'Serak': ('Rigel VII', 'Preparer'),
         b'Zim': ('Irk', 'Invader'),
         b'Lrrr': ('Omicron Persei 8', 'Emperor')}

        Returned keys are always bytes. If a key from the keys argument is
        missing from the dictionary, then that row was not found in the
        table (and require_all_keys must have been False).

    Raises:
        IOError: An error occurred accessing the smalltable.
    """

class SampleClass:
    """Summary of class here.

    Longer class information...
    Longer class information...

    Attributes:
        likes_spam: A boolean indicating if we like SPAM or not.
        eggs: An integer count of the eggs we have laid.
    """

    def __init__(self, likes_spam: bool = False):
        """Initializes the instance based on spam preference.

        Args:
          likes_spam: Defines if instance exhibits this preference.
        """
        self.likes_spam = likes_spam
        self.eggs = 0

"""A one-line summary of the module or program, terminated by a period.

Leave one blank line. The rest of this docstring should contain an
overall description of the module or program. Optionally, it may also
contain a brief description of exported classes and functions and/or usage
examples.

Typical usage example:

  foo = ClassFoo()
  bar = foo.function_bar()
"""

def func(a: int) -> list[int]:
    return [a * 2]

# For variables when type isn't obvious
a: SomeType = some_func()

# Use modern syntax (Python 3.10+)
def process(data: str | None = None) -> dict[str, int]:
    pass

from typing import Dict, List, Set, Tuple, Optional

# Good - using typing module
def process_users(users: List[str]) -> Dict[str, int]:
    return {user: len(user) for user in users}

def get_config() -> Dict[str, List[int]]:
    return {"ports": [8080, 8081]}

# Good - with Optional
def find_user(user_id: int) -> Optional[str]:
    return None

# Bad - using built-in lowercase types (avoid)
def process_users(users: list[str]) -> dict[str, int]:
    return {user: len(user) for user in users}

# Good
foo_bar(
    self, width, height, color='black', design=None, x='foo',
    emphasis=None, highlight=0
)

# Good
if (width == 0 and height == 0 and
    color == 'red' and emphasis == 'strong'):
    pass

# Bad - backslash continuation
if width == 0 and height == 0 and \
    color == 'red' and emphasis == 'strong':
    pass

# Good
def connect_to_next_port(self, minimum: int) -> int:
    """Connects to the next available port.

    Args:
        minimum: A port value greater or equal to 1024.

    Returns:
        The new minimum port.

    Raises:
        ConnectionError: If no available port is found.
    """
    if minimum < 1024:
        raise ValueError(f'Min. port must be at least 1024, not {minimum}.')
    
    port = self._find_next_port(minimum)
    if port is None:
        raise ConnectionError(
            f'Could not connect to service on port {minimum} or higher.')
    return port

# Good
def foo(a, b: list[int] | None = None):
    if b is None:
        b = []

# Bad
def foo(a, b: list[int] = []):
    pass

# Good
if not users:
    print('no users')

if foo:
    bar()

# Check for None explicitly
if x is None:
    pass

# Bad
if len(users) == 0:
    print('no users')

if foo != []:
    bar()

# Good
result = [mapping_expr for value in iterable if filter_expr]

# Good
result = [
    is_valid(metric={'key': value})
    for value in interesting_iterable
    if a_longer_filter_expression(value)
]

# Bad - multiple for clauses
result = [(x, y) for x in range(10) for y in range(5) if x * y > 10]

# Good - using underscore when variable is not used
for _user in users:
    print("Processing a user")
    send_notification()

for _item in items:
    count += 1

# Good - using the variable
for user in users:
    print(f"Processing {user.name}")
    user.process()

# Bad - not using underscore when variable is unused
for user in users:  # 'user' is never referenced
    print("Processing a user")

def do_PUT(self):  # WSGI name, so pylint: disable=invalid-name
    pass

import this