# Naming
class MyClass: ...              # CamelCase for classes
def my_function(): ...         # snake_case for functions
MY_CONSTANT = 42               # UPPER_SNAKE_CASE for constants
_instance = SomeClass()        # _prefix for private

# Imports (on separate lines)
# Bad: import sys, os
# Good:
import sys
import os
from typing import Optional

# Line length: 88 characters (Black default)
# Line breaks: align with opening delimiter
result = some_function(
    arg1, arg2, arg3,
    arg4, arg5, arg6,
)

# Spaces around operators
# Bad: x=1+2
# Good: x = 1 + 2

# Blank lines
class MyClass:
    """Docstring."""            # 2 blank lines after docstring


    def method(self):           # 2 blank lines between methods
        ...

"""Module-level docstring.

One blank line after, then imports.
"""

class Calculator:
    """Perform arithmetic operations.

    This class provides basic math functions.

    Example:
        >>> calc = Calculator()
        >>> calc.add(2, 3)
        5
    """

    def add(self, a: int, b: int) -> int:
        """Add two numbers.

        Args:
            a: First number.
            b: Second number.

        Returns:
            Sum of a and b.

        Raises:
            ValueError: If inputs are not integers.
        """
        if not isinstance(a, int) or not isinstance(b, int):
            raise ValueError("Inputs must be integers")
        return a + b

# Loop with index
for i, item in enumerate(items):
    ...

# Multiple assignments
a, b = b, a  # Swap

# List comprehension (preferred)
squares = [x*x for x in range(10)]

# Generator for large sequences
def get_lines(filename):
    with open(filename) as f:
        for line in f:
            yield line

# Context managers
with open("file.txt") as f:
    data = f.read()

# Multiple context managers
with open("input.txt") as infile, open("output.txt", "w") as outfile:
    outfile.write(infile.read())

# Ternary operator
value = "positive" if x > 0 else "non-positive"

# Check membership (not len)
if items:  # Not if len(items) > 0
    ...

# Merge dictionaries (3.9+)
d1 = {"a": 1}
d2 = {"b": 2}
merged = d1 | d2