match语句
Switch 语句存在于很多编程语言中，早在 2016 年，PEP 3103 就被提出，建议 Python 支持 switch-case 语句。
时间在推到 2020 年，Python的创始人Guido van Rossum，提交了显示 switch 语句的第一个文档，命名为 Structural Pattern Matching。
如今，随着 Python 3.10 beta 版的发布，终于将 switch-case 语句纳入其中。
在 Python 中，这一功能由 match 关键词和 case 语句组成。
最简单的例子
一个值，即主词，被匹配到几个字面值，即模式。在下面的例子中，status 是匹配语句的主词。模式是每个 case 语句，字面值代表请求状态代码。匹配后，将执行与该 case 相关的动作
def http_error(status):
match status:
case 400:
return "Bad request"
case 404:
return "Not found"
case 418:
return "I'm a teapot"
case 401 | 403 | 404:
return "Not allowed"
case _:
return "Something's wrong with the internet"
mystr = http_error(500)
print(mystr)运行结果：
Something's wrong with the internet直接使用
coordinate = (0, 6)
match coordinate:
case (0, 0):
print("Origin")
case (0, y):
print(f"Y={y}")
case (x, 0):
print(f"X={x}")
case (x, y):
print(f"X={x}, Y={y}")
case _:
raise ValueError("Not a coordinate")运行结果：
Y=6类中使用
如果你使用类来结构化你的数据，你可以使用类的名字，后面跟一个类似构造函数的参数列表，作为一种模式。这种模式可以将类的属性捕捉到变量中:
class Point:
def __init__(self, a, b):
self.a = a
self.b = b
def location(point):
match point:
case Point(a=0, b=0):
print("Origin is the point's location.")
case Point(a=0, b=b):
print(f"Y={b} and the point is on the y-axis.")
case Point(a=a, b=0):
print(f"a={a} and the point is on the x-axis.")
case Point():
print("The point is located somewhere else on the plane.")
case _:
print("Not a point")
point = Point(0, 1)
location(point)运行结果：
Y=1 and the point is on the y-axis.我们可以向一个模式添加 if 子句，称为“约束项”。 如果约束项为假值，则 match 将继续尝试下一个 case 语句块。 请注意值的捕获发生在约束项被求值之前。:
class Point:
def __init__(self, x, y):
self.x = x
self.y = y
point = Point(x=0, y=0)
match point:
case Point(x=x, y=y) if x == y:
print(f"The point is located on the diagonal Y=X at {x}.")
case Point(x=x, y=y):
print(f"Point is not on the diagonal.")
运行结果：
The point is located on the diagonal Y=X at 0.例：
from enum import Enum
class Color(Enum):
RED = 0
GREEN = 1
BLUE = 2
match color:
case Color.RED:
print("I see red!")
case Color.GREEN:
print("Grass is green")
case Color.BLUE:
print("I'm feeling the blues :(")运行结果：
Enter your choice of 'red', 'blue' or 'green': red
I see red!复杂一点的例子
def func(person):
match person:
case (name, "teacher"):
print(f"{name} is a teacher.")
case (name, _, "male"):
print(f"{name} is male.")
case (name, _, "female"):
print(f"{name} is female.")
case (name, age, gender):
print(f"{name} is {age} old.")运行结果：
Sam is a teacher.
John is male.
John is female.
John is 25 old.官方文档：