Standard Library Mastery
Pathlib for File Operations
from pathlib import Path
# Path creation and manipulation
project_root = Path(__file__).parent.parent
config_file = project_root / "config" / "settings.toml"
data_dir = Path.home() / "data"
# File operations
def read_config(config_path: Path) -> dict[str, str]:
if not config_path.exists():
raise FileNotFoundError(f"Config not found: {config_path}")
# Read text
content = config_path.read_text(encoding="utf-8")
# Read bytes
binary = config_path.read_bytes()
return parse_config(content)
# Path traversal
def find_python_files(directory: Path) -> list[Path]:
# Recursive glob
return list(directory.rglob("*.py"))
def get_file_info(path: Path) -> dict[str, Any]:
stat = path.stat()
return {
"size": stat.st_size,
"modified": stat.st_mtime,
"is_file": path.is_file(),
"is_dir": path.is_dir(),
"suffix": path.suffix,
"stem": path.stem,
}
# Creating directories
def ensure_dir(path: Path) -> None:
path.mkdir(parents=True, exist_ok=True)
# Temporary files
from tempfile import TemporaryDirectory
from pathlib import Path
def process_with_temp() -> None:
with TemporaryDirectory() as tmpdir:
temp_path = Path(tmpdir) / "output.txt"
temp_path.write_text("data")
Dataclasses for Data Structures
from dataclasses import dataclass, field, asdict, replace
from typing import ClassVar
# Basic dataclass
@dataclass
class User:
id: int
name: str
email: str
active: bool = True
# Post-init processing
@dataclass
class Product:
name: str
price: float
discount: float = 0.0
def __post_init__(self) -> None:
if self.discount > 1.0:
raise ValueError("Discount must be <= 1.0")
@property
def final_price(self) -> float:
return self.price * (1 - self.discount)
# Field with factory
@dataclass
class ShoppingCart:
user_id: int
items: list[str] = field(default_factory=list)
metadata: dict[str, Any] = field(default_factory=dict)
# Frozen dataclass (immutable)
@dataclass(frozen=True)
class Point:
x: float
y: float
def distance(self, other: "Point") -> float:
return ((self.x - other.x)**2 + (self.y - other.y)**2)**0.5
# Class variables
@dataclass
class Config:
API_VERSION: ClassVar[str] = "v1"
BASE_URL: ClassVar[str] = "https://api.example.com"
timeout: int = 30
retries: int = 3
# Ordered dataclass for comparison
@dataclass(order=True)
class Priority:
level: int
name: str = field(compare=False)
# Convert to/from dict
user = User(1, "Alice", "alice@example.com")
user_dict = asdict(user)
updated = replace(user, name="Alice Smith")
Functools for Function Tools
from functools import (
cache, lru_cache, cached_property,
partial, wraps, reduce, singledispatch
)
# Caching
@cache # Unlimited cache (Python 3.9+)
def fibonacci(n: int) -> int:
if n < 2:
return n
return fibonacci(n - 1) + fibonacci(n - 2)
@lru_cache(maxsize=128) # LRU cache with size limit
def fetch_user(user_id: int) -> dict[str, Any]:
# Expensive database call
return {"id": user_id, "name": "User"}
# Cached property
class DataProcessor:
def __init__(self, data: list[int]) -> None:
self._data = data
@cached_property
def mean(self) -> float:
"""Computed once, then cached."""
return sum(self._data) / len(self._data)
# Partial application
from operator import mul
double = partial(mul, 2)
triple = partial(mul, 3)
print(double(5)) # 10
# Decorator preservation
def timing_decorator(func: Callable[P, R]) -> Callable[P, R]:
@wraps(func)
def wrapper(*args: P.args, **kwargs: P.kwargs) -> R:
start = time.time()
result = func(*args, **kwargs)
print(f"{func.__name__} took {time.time() - start:.2f}s")
return result
return wrapper
# Reduce for aggregation
from operator import add
total = reduce(add, [1, 2, 3, 4, 5]) # 15
product = reduce(mul, [1, 2, 3, 4], 1) # 24
# Single dispatch for polymorphism
@singledispatch
def process(arg: Any) -> str:
return f"Unknown type: {type(arg)}"
@process.register
def _(arg: int) -> str:
return f"Integer: {arg * 2}"
@process.register
def _(arg: str) -> str:
return f"String: {arg.upper()}"
@process.register(list)
def _(arg: list[Any]) -> str:
return f"List with {len(arg)} items"
Itertools for Iteration
from itertools import (
chain, islice, cycle, repeat,
groupby, accumulate, combinations, permutations,
product, zip_longest, tee, filterfalse
)
# Chain multiple iterables
combined = list(chain([1, 2], [3, 4], [5, 6])) # [1,2,3,4,5,6]
# Slice iterator (memory efficient)
first_10 = list(islice(range(1000), 10))
# Infinite iterators
from itertools import count
counter = count(start=1, step=2) # 1, 3, 5, 7, ...
# Groupby for grouping
data = [("A", 1), ("A", 2), ("B", 1), ("B", 2)]
grouped = {k: list(v) for k, v in groupby(data, key=lambda x: x[0])}
# Accumulate for running totals
cumsum = list(accumulate([1, 2, 3, 4, 5])) # [1, 3, 6, 10, 15]
# Combinations and permutations
combos = list(combinations([1, 2, 3], 2)) # [(1,2), (1,3), (2,3)]
perms = list(permutations([1, 2, 3], 2)) # [(1,2), (1,3), (2,1), ...]
# Cartesian product
pairs = list(product([1, 2], ['a', 'b'])) # [(1,'a'), (1,'b'), (2,'a'), (2,'b')]
# Zip with different lengths
from itertools import zip_longest
paired = list(zip_longest([1, 2], ['a', 'b', 'c'], fillvalue=0))
# Tee for multiple iterators
it1, it2 = tee(range(5), 2)
# Filter false
odds = list(filterfalse(lambda x: x % 2 == 0, range(10)))
Collections for Data Structures
from collections import (
defaultdict, Counter, deque, namedtuple,
ChainMap, OrderedDict
)
# defaultdict for automatic defaults
word_index: defaultdict[str, list[int]] = defaultdict(list)
for i, word in enumerate(["hello", "world", "hello"]):
word_index[word].append(i)
# Counter for counting
from collections import Counter
word_counts = Counter(["apple", "banana", "apple", "cherry", "banana", "apple"])
print(word_counts.most_common(2)) # [('apple', 3), ('banana', 2)]
# Counter operations
c1 = Counter(a=3, b=1)
c2 = Counter(a=1, b=2)
print(c1 + c2) # Counter({'a': 4, 'b': 3})
# deque for efficient queue operations
from collections import deque
queue: deque[str] = deque()
queue.append("first")
queue.append("second")
queue.appendleft("priority")
item = queue.popleft() # "priority"
# Ring buffer with maxlen
recent: deque[int] = deque(maxlen=3)
for i in range(5):
recent.append(i) # Only keeps last 3
# namedtuple for lightweight classes
from collections import namedtuple
Point = namedtuple('Point', ['x', 'y'])
p = Point(1, 2)
print(p.x, p.y)
# ChainMap for layered configs
from collections import ChainMap
defaults = {'color': 'red', 'user': 'guest'}
environment = {'user': 'admin'}
combined = ChainMap(environment, defaults)
print(combined['user']) # 'admin' (from environment)
Context Managers
from contextlib import contextmanager, suppress, ExitStack
# Custom context manager
@contextmanager
def managed_resource(resource_id: str) -> Iterator[Resource]:
resource = acquire_resource(resource_id)
try:
yield resource
finally:
release_resource(resource)
# Suppress exceptions
with suppress(FileNotFoundError):
Path("nonexistent.txt").unlink()
# ExitStack for dynamic context managers
def process_files(filenames: list[str]) -> None:
with ExitStack() as stack:
files = [stack.enter_context(open(fn)) for fn in filenames]
# All files auto-closed on exit
for f in files:
process(f.read())
Enum for Constants
from enum import Enum, auto, IntEnum, Flag
# Basic enum
class Status(Enum):
PENDING = "pending"
APPROVED = "approved"
REJECTED = "rejected"
# Auto values
class Color(Enum):
RED = auto()
GREEN = auto()
BLUE = auto()
# IntEnum for numeric values
class Priority(IntEnum):
LOW = 1
MEDIUM = 2
HIGH = 3
# Flag for bit flags
class Permission(Flag):
READ = auto()
WRITE = auto()
EXECUTE = auto()
user_perms = Permission.READ | Permission.WRITE
if Permission.READ in user_perms:
print("Can read")
Logging
import logging
from pathlib import Path
# Configure logging
logging.basicConfig(
level=logging.INFO,
format='%(asctime)s - %(name)s - %(levelname)s - %(message)s',
handlers=[
logging.FileHandler('app.log'),
logging.StreamHandler()
]
)
logger = logging.getLogger(__name__)
# Structured logging
def process_user(user_id: int) -> None:
logger.info("Processing user", extra={"user_id": user_id})
try:
# Process...
logger.debug("User data loaded", extra={"user_id": user_id})
except Exception as e:
logger.exception("Failed to process user", extra={"user_id": user_id})
