# Essential built-ins
len([1, 2, 3])              # 3
sum([1, 2, 3])              # 6
min([3, 1, 4])              # 1
max([3, 1, 4])              # 4
sorted([3, 1, 4])           # [1, 3, 4]
reversed([1, 2, 3])         # iterator: 3, 2, 1
enumerate(['a', 'b', 'c'])  # (0,'a'), (1,'b'), (2,'c')
zip([1, 2], ['a', 'b'])     # (1,'a'), (2,'b')
map(str, [1, 2, 3])         # ['1', '2', '3']
filter(bool, [0, 1, '', 'a'])  # [1, 'a']
any([False, True, False])   # True
all([True, True, False])    # False

from collections import defaultdict, Counter, deque, namedtuple

# defaultdict - dict with default factory
word_count = defaultdict(int)
for word in words:
    word_count[word] += 1

# Counter - count hashable objects
Counter(['a', 'b', 'a', 'c', 'a'])  # Counter({'a': 3, 'b': 1, 'c': 1})
Counter("hello").most_common(2)    # [('l', 2), ('h', 1)]

# deque - double-ended queue
d = deque([1, 2, 3], maxlen=5)
d.appendleft(0)  # [0, 1, 2, 3]
d.pop()          # 3

# namedtuple - lightweight class
Point = namedtuple('Point', ['x', 'y'])
p = Point(3, 4)
p.x, p.y  # 3, 4

from functools import lru_cache, partial, reduce

# lru_cache - memoization
@lru_cache(maxsize=128)
def fibonacci(n):
    if n < 2:
        return n
    return fibonacci(n-1) + fibonacci(n-2)

# partial - fix function arguments
from operator import mul
double = partial(mul, 2)
double(5)  # 10

# reduce - fold a sequence
reduce(lambda x, y: x + y, [1, 2, 3, 4])  # 10

from pathlib import Path

# Path operations
p = Path("/home/user/documents")
p / "file.txt"           # /home/user/documents/file.txt
p.exists()               # True/False
p.is_dir()               # True
p.parent                 # /home/user
p.name                   # documents
p.suffix                 # '' (no extension)

# File operations
Path("file.txt").read_text()
Path("file.txt").write_text("content")
list(Path(".").glob("*.py"))  # all Python files

import json

# Serialize
data = {"name": "Alice", "age": 30}
json_str = json.dumps(data, indent=2)
Path("data.json").write_text(json_str)

# Deserialize
loaded = json.loads(json_str)
data = json.loads(Path("data.json").read_text())

from typing import Optional, List, Dict, Callable, TypeVar

def greet(name: str) -> str:
    return f"Hello, {name}"

def process(items: List[int]) -> Dict[str, int]:
    return {"sum": sum(items), "count": len(items)}

def maybe_int(value: str) -> Optional[int]:
    try:
        return int(value)
    except ValueError:
        return None

# Generic types
T = TypeVar('T')
def first(items: List[T]) -> Optional[T]:
    return items[0] if items else None