py语法糖

大数定义

title:Example
定义一个10亿整数

# 法一
a = 10 * 10000 * 10000
# 法二
b = 10_0000_0000
# 法三
c = 10 ** 9
# 以上结果都是10亿

变量值交换

title:Example
交换变量整数

a, b = b, a
# a与b交换

逻辑判断

title:Example
逻辑判断

在c中

if(a >= 90 && a <= 100){;}

在python中

if 90 <= a <= 100:

合并列表

extend的取代方法

a = [1, 2, 3]
b = [4, 5, 6, 7, 8, 9]
print(a + b)
# output:[1, 2, 3, 4, 5, 6, 7, 8, 9]

列表推导式

title:Example
列表所有数据+233

a = [1, 2, 3, 4]
 
# 法一
b = []
for e in a:
    b.append(e+233)
 
# 法二
b = [ e+233  for e in a]
 
# output:[234, 235, 236, 237]

字典推导式

适合把两个序列组合成映射，或对原字典做简单转换。

names = ["Tom", "Lucy", "Jack"]
scores = [80, 95, 72]
 
score_map = {name: score for name, score in zip(names, scores)}
print(score_map)
# output:{'Tom': 80, 'Lucy': 95, 'Jack': 72}
 
passed = {name: score for name, score in score_map.items() if score >= 80}
print(passed)
# output:{'Tom': 80, 'Lucy': 95}

集合推导式

适合去重后再加工。

numbers = [1, 2, 2, 3, 4, 4]
even_squares = {x * x for x in numbers if x % 2 == 0}
print(even_squares)
# output:{16, 4}

生成器表达式

生成器不会一次性创建完整列表，适合大数据量的逐个处理。

total = sum(x * x for x in range(1, 101))
print(total)
# output:338350

三元表达式

age = 20
status = "成年" if age >= 18 else "未成年"
print(status)
# output:成年

enumerate

替代手写下标变量。

names = ["Tom", "Lucy", "Jack"]
for index, name in enumerate(names, start=1):
    print(index, name)

zip

用于并行遍历多个容器。

names = ["Tom", "Lucy"]
scores = [80, 95]
 
for name, score in zip(names, scores):
    print(f"{name}: {score}")

解包

普通解包

point = (3, 5)
x, y = point
print(x, y)

星号解包

numbers = [1, 2, 3, 4, 5]
first, *middle, last = numbers
print(first, middle, last)
# output:1 [2, 3, 4] 5

函数参数解包

def add(a, b):
    return a + b
 
args = [10, 20]
print(add(*args))
 
kwargs = {"a": 10, "b": 20}
print(add(**kwargs))

合并字典

base = {"host": "localhost", "port": 3306}
override = {"port": 3307, "user": "root"}
 
config1 = {**base, **override}
config2 = base | override
 
print(config1)
print(config2)

| 合并字典需要 Python 3.9+。

with 上下文管理器

自动处理资源释放，常用于文件、锁、网络连接等对象。

with open("demo.txt", "w", encoding="utf-8") as file:
    file.write("hello")

lambda

适合非常短的小函数，复杂逻辑应改成普通 def。

students = [("Tom", 80), ("Lucy", 95), ("Jack", 72)]
students.sort(key=lambda item: item[1], reverse=True)
print(students)

walrus 海象运算符

:= 可以在表达式中赋值，需要 Python 3.8+。

text = "python"
if (length := len(text)) > 5:
    print(length)

match case

结构化模式匹配，需要 Python 3.10+。

command = ("move", 10, 20)
 
match command:
    case ("move", x, y):
        print(f"move to {x}, {y}")
    case ("quit",):
        print("quit")
    case _:
        print("unknown command")

装饰器

装饰器本质是“接收函数并返回新函数”的函数，常用于日志、计时、权限检查。

def trace(func):
    def wrapper(*args, **kwargs):
        print(f"call {func.__name__}")
        return func(*args, **kwargs)
    return wrapper
 
@trace
def hello(name):
    return f"hello {name}"
 
print(hello("Tom"))

装饰器内容较多，单独说明见：py装饰器。

f-string

name = "Tom"
score = 95.678
 
print(f"{name} score={score:.2f}")
# output:Tom score=95.68

语法糖使用原则

1. 能明显减少样板代码时使用。
2. 一行表达式太长、嵌套太深时，不要强行使用语法糖。
3. 推导式适合简单映射和过滤，复杂流程用普通循环。
4. lambda 适合短逻辑，复杂逻辑写成具名函数。
5. 注意版本要求：:= 需要 Python 3.8+，dict | dict 需要 Python 3.9+，match case 需要 Python 3.10+。

案例

py语法糖案例

Python 语法糖案例

下面这段代码集中演示常见语法糖，可以直接复制到 .py 文件中运行。

def trace(func):
    def wrapper(*args, **kwargs):
        print(f"call {func.__name__}")
        return func(*args, **kwargs)
 
    return wrapper
 
 
@trace
def greet(name):
    return f"hello {name}"
 
 
def main():
    billion = 10_0000_0000
    print("big int:", billion == 10**9)
 
    a, b = 1, 2
    a, b = b, a
    print("swap:", a, b)
 
    score = 95
    print("chain compare:", 90 <= score <= 100)
 
    numbers = [1, 2, 3, 4]
    print("list comprehension:", [x + 233 for x in numbers])
    print("dict comprehension:", {x: x * x for x in numbers})
    print("set comprehension:", {x % 3 for x in numbers})
    print("generator expression:", sum(x * x for x in numbers))
 
    age = 20
    print("ternary:", "adult" if age >= 18 else "child")
 
    first, *middle, last = [1, 2, 3, 4]
    print("star unpack:", first, middle, last)
 
    def add(a, b):
        return a + b
 
    print("args unpack:", add(*[10, 20]))
    print("kwargs unpack:", add(**{"a": 10, "b": 20}))
 
    base = {"host": "localhost", "port": 3306}
    override = {"port": 3307, "user": "root"}
    print("dict merge:", base | override)
 
    text = "python"
    if (length := len(text)) > 5:
        print("walrus:", length)
 
    command = ("move", 10, 20)
    match command:
        case ("move", x, y):
            print("match:", x, y)
        case _:
            print("match: unknown")
 
    print(greet("Tom"))
 
 
if __name__ == "__main__":
    main()

指向原始笔记的链接