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【Python笔记】函数

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Python学习笔记

1、定义

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def function():
    print("This is a function.")


if __name__ == "__main__":
    function()

2、参数

  • 必备参数
  • 关键字参数
  • 默认参数
  • 不定长参数
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def add(a, b):
    return a + b


def demo_1():
    print("Demo 1:")
    print(add(1, 2))


def sum_abcd(a, b, c=0, d=0):
    return a + b + c + d


def demo_2():
    print("Demo 2:")
    print(sum_abcd(1, 2, 3, 4))
    print(sum_abcd(1, 2, c=3, d=4))
    print(sum_abcd(1, 2, d=4))
    print(sum_abcd(1, d=4, b=2))
    # print(sum_abcd(1, c=3, d=4))
    pass


def max(*args):
    print(type(args))  # tuple
    print(args)
    num = len(args)
    if num == 0:
        return None
    ret = args[0]
    for item in args:
        if item > ret:
            ret = item
    return ret


def demo_3():
    print("Demo 3:")
    print(max())
    print(max(1, 2, 3, 4, 5, 6))
    arr = (1, 2, 3, 4, 5, 6)
    print(max(*arr))
    arr = [1, 2, 3, 4, 5, 6]
    print(max(*arr))


def print_dict(**args):
    print(type(args))  # dict
    print(args)
    num = len(args)
    if num == 0:
        print(None)
    for key, value in args.items():
        print(f"{key} = {value}")
    pass


def demo_4():
    print("Demo 4:")
    print_dict()
    print_dict(a=1, b=2, c=3, d=4)
    dic = {"a": 1, "b": 2, "c": 3, "d": 4}
    print_dict(**dic)
    print(sum_abcd(**dic))


def test_var_args(a, b, *args, **kwargs):
    print(f"a = {a}")
    print(f"b = {b}")
    print(args)
    print(kwargs)
    pass


def demo_5():
    print("Demo 5:")
    test_var_args(1, 2, 3, 4, e=5, f=6)
    test_var_args(1, 2, 3, 4)
    test_var_args(1, 2, e=5, f=6)
    pass


if __name__ == "__main__":
    demo_1()
    demo_2()
    demo_3()
    demo_4()
    demo_5()
    pass

3、参数传递

  • 不可变类型:

    整数、浮点数、字符串、元组

  • 可变类型

    列表、字典、自定义类

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def change_1(a: int, b: float, c: str, d: tuple):
    a -= 10
    b -= 10.0
    c = c.replace("Hello", "Hi")
    # d[0] = 5
    pass


def demo_1():
    print("Demo 1:")
    a = 5
    b = 5.0
    c = "Hello World!"
    d = (1, 2, 3, 4)
    change_1(a, b, c, d)
    """ a=5, b=5.0, c=Hello World!, d=(1, 2, 3, 4) """
    print(f"a={a}, b={b}, c={c}, d={d}")
    pass


def change_2(a: list, b: dict):
    a.reverse()
    for key in b.keys():
        b[key] *= 10
    pass


def demo_2():
    print("Demo 2:")
    a = [1, 2, 3, 4]
    b = {"a": 1, "b": 2}
    change_2(a, b)
    """ a=[4, 3, 2, 1], b={'a': 10, 'b': 20} """
    print(f"a={a}, b={b}")
    pass


class MyClass():

    def __init__(self) -> None:
        self.a = 0
        self.b = 0
        pass

    def __str__(self) -> str:
        return f"a={self.a}, b={self.b}"
        pass


def change_3(obj: MyClass):
    obj.a = 10
    obj.b = 20
    pass


def demo_3():
    print("Demo 3:")
    obj = MyClass()
    change_3(obj)
    """ a=10, b=20 """
    print(obj)


if __name__ == "__main__":
    demo_1()
    demo_2()
    demo_3()
    pass

4、返回值

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def return_value_1():
    pass


def demo_1():
    print("Demo 1:")
    ret = return_value_1()
    print(ret)  # None
    pass


def return_value_2(a, b):
    return a + b


def demo_2():
    print("Demo 2:")
    ret = return_value_2(1, 2)
    print(ret)  # 3
    pass


def return_value_3(a, b, c):
    a += 10
    b += 10
    c += 10
    return a, b, c


def demo_3():
    print("Demo 3:")
    ret = return_value_3(1, 2, 3)
    print(ret)  # (11, 12, 13)
    a, b, c = return_value_3(1, 2, 3)
    print(f"a={a}, b={b}, c={c}")  # a=11, b=12, c=13
    # a, b = return_value_3(1, 2, 3)
    # a, b, c, d = return_value_3(1, 2, 3)
    pass


def return_value_4():
    return return_value_2


def demo_4():
    print("Demo 3:")
    add = return_value_4()
    ret = add(1, 2)
    print(ret)  # 3
    pass


if __name__ == "__main__":
    demo_1()
    demo_2()
    demo_3()
    demo_4()
    pass

5、匿名函数

lambda函数的语法只包含一个语句

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lambda [arg1 [,arg2,.....argn]]:expression
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def demo_1():
    print("Demo 1:")
    sq = lambda x: x**2
    ret = sq(10)
    print(ret)  # 100
    pass


def demo_2():
    print("Demo 2:")
    """ lambda [arg1 [,arg2,.....argn]]:expr1 if condition else expr2 """
    max = lambda x, y: x if x > y else y
    ret = max(10, 100)
    print(ret)  #100
    pass


if __name__ == "__main__":
    demo_1()
    demo_2()
    pass

6、作用域

全局变量与 局部变量

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# total = 0  # 全局变量


def demo_1():
    total = 100  # 局部变量
    pass


def demo_2(total):
    total = 100
    pass


def demo_3():
    global total
    total = 100  # 全局变量
    pass


def demo_4(total):
    # global total  # "total" is assigned before global declaration
    total = 100
    pass


def demo_5():
    global g_total
    g_total = 100
    pass


if __name__ == "__main__":
    total = 0
    demo_1()
    print(total)  # 全局变量total: 0

    total = 0
    demo_2(total)
    print(total)  # 全局变量total: 0

    total = 0
    demo_3()
    print(total)  # 全局变量total: 100

    demo_5()
    print(g_total)  # 全局变量g_total: 100
    pass

LEGB规则

Python按以下顺序依次进行查找符号对应的对象

locals $\to$ enclosing $\to$ globals $\to$ build-in

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""" LEGB规则 """


def demo_1():
    tmp = 10
    print(tmp)  # 局部变量


def sq(x):
    print(f"Global function sq, x={x}")
    pass


def demo_2(a):

    def sq(x):
        return x**a  # 嵌套作用域

    return sq(2)


def demo_3():
    print(total)  # 全局变量


def demo_4():
    print(__name__)  # 内置作用域


if __name__ == "__main__":
    demo_1()

    ret = demo_2(10)
    print(ret)

    total = 100
    demo_3()

    demo_4()
    pass