《Python编程入门》附录 A：Python 语法速查表

>>> 2 ** 3 ** 2
512                          # 右结合，等价于 2 ** (3 ** 2)
>>> -2 ** 2
-4                           # 一元负号优先级低于 **
>>> 1 < 2 < 3
True                         # 链式比较等价于 (1 < 2) and (2 < 3)

>>> s = "abcdef"
>>> s[1:4], s[:3], s[3:], s[::2], s[::-1]
('bcd', 'abc', 'def', 'ace', 'fedcba')
>>> nums = [0, 1, 2, 3, 4, 5]
>>> nums[1:5:2]
[1, 3]
>>> nums[::-1]
[5, 4, 3, 2, 1, 0]

>>> [i * i for i in range(5)]
[0, 1, 4, 9, 16]
>>> [i for i in range(10) if i % 2 == 0]
[0, 2, 4, 6, 8]
>>> {c: ord(c) for c in "abc"}
{'a': 97, 'b': 98, 'c': 99}
>>> {c for c in "aabbcc"}
{'a', 'b', 'c'}
>>> list(zip([1, 2, 3], "abc"))
[(1, 'a'), (2, 'b'), (3, 'c')]

def f(a, b=2, *args, c, d=4, **kw):
    return a, b, args, c, d, kw

>>> f(1, 9, 8, 7, c=3, x=5)
(1, 9, (8, 7), 3, 4, {'x': 5})

def g(a, /, b, *, c):
    return a, b, c

>>> g(1, 2, c=3)
(1, 2, 3)

counter = 0

def inc():
    global counter
    counter += 1

def outer():
    n = 0
    def inner():
        nonlocal n
        n += 1
        return n
    return inner

>>> inc(); counter
1
>>> h = outer(); h(), h(), h()
(1, 2, 3)

class Animal:
    kind = "animal"                 # 类属性，所有实例共享

    def __init__(self, name):
        self.name = name            # 实例属性

    def speak(self):
        return f"{self.name} makes a sound"

class Dog(Animal):
    def speak(self):                # 覆写父类方法
        return f"{self.name} barks"

>>> Dog("Rex").speak(), Dog.kind, Animal.kind
('Rex barks', 'animal', 'animal')
>>> issubclass(Dog, Animal), isinstance(Dog("Rex"), Animal)
(True, True)

def parse(v):
    try:
        return int(v)
    except ValueError as e:
        return f"bad: {e}"
    except (TypeError, OverflowError):
        return "wrong type"
    else:
        ...              # 没有异常时执行
    finally:
        ...              # 无论如何都执行，用于释放资源

def describe(v):
    match v:
        case int():
            return "int"
        case str() if v == "a":
            return "str-a"
        case [x, y]:
            return f"pair {x},{y}"
        case {"type": "point", "x": x, "y": y}:
            return f"point {x},{y}"
        case _:
            return "other"

>>> describe(1), describe("a"), describe([1, 2]), describe({"type": "point", "x": 1, "y": 2})
('int', 'str-a', 'pair 1,2', 'point 1,2')

def greet(name: str, times: int = 1) -> str:
    return (name + " ") * times

x: int | None = None            # 3.10+ 用 | 表示联合
pairs: list[tuple[str, int]] = []

# PEP 695（3.12+）：类型别名与泛型用新语法
type Vector = list[float]

def first[T](xs: list[T]) -> T:
    return xs[0]

class Stack[T]:
    def __init__(self) -> None:
        self._items: list[T] = []

    def push(self, item: T) -> None:
        self._items.append(item)

    def pop(self) -> T:
        return self._items.pop()

>>> name, score = "Ada", 3.14159
>>> f"{name} got {score:.2f}, hex {255:#x}, pct {0.256:.1%}, comma {1234567:,}"
'Ada got 3.14, hex 0xff, pct 25.6%, comma 1,234,567'