函数定义

def 函数名(形参列表用逗号隔开)：

     函数体

     return 返回值

# 有参数 无返回值
def my_length(data):
    count = 0
    for i in data:
        count += 1
    
    print(f"data count={count}")

my_length(str1)
my_length(str2)

#无参数无返回值
def say_hello():
    print("hello python")


say_hello()




有参数 有返回值
def sum(x,y):
    result = x + y
    return result
a = 2
b =  5
result = sum(a,b)
print(f"{a} sum {b} = {sum(a,b)}")




def smile():
    print("give me a hug")
    return  None

result = smile()
print(f"result = {result}")

result = sum(a,b)
print(f"{a} sum {b} = {a + b}")
 


#None
name = None

if name:
    print("name = 不为空")
else:
    print(f"name = {name}")

#函数说明文档
def mulity(x,y):
    """
    两个数字相乘
    :param x: 乘数
    :param y: 被乘数
    :return result: 积
    """
    result = x * y
    return result
result = mulity(10,20)
print(f"{10} * {20} = {10 * 20}")

变量作用域

、

num = 20

def test_a():
    print("test_a",{num})

def test_b():
    global num
    num = 500
    print("test_b",{num})


test_a()
test_b()
print("num=%d" % num)

money = 5000000000
name = None

name = input("请输入你的名字")


def query(show_header):
    if show_header:
        print("===========查询余额========")
    print(f"{name}， 您好 您的余额为：{money}")

def saving(num):
    global money
    money += num
    print("===========存款=======")
    print(f"{name}， 您好 您存款：{num}元成功")

    query(False)

def get_money(num):
    global money
    money -= num
    print("===========取款=======")
    print(f"{name}， 您好 您存款：{num}元成功")
    query(False)

def main():
    print("==========主菜单=======")
    print(f"{name}， 您好 xxx银行为您服务 请选择你需要的服务")
    print("余额查询\t【请输入1】")
    print("存款\t\t【请输入2】")
    print("取款\t\t【请输入3】")
    print("退出\t\t【请输入4】")
    return input("请输入您的选择：")


while True:
    keyboard_input = main()
    if keyboard_input == "1":
        query(True)
        continue
    elif keyboard_input == "2":
        num = int(input("请存放xx币"))
        saving(num)
        continue
    elif keyboard_input == "3":
        num = int(input("请输入取款金额"))
        get_money(num)
        continue
    else:
        print("很高兴为你服务 欢迎下次光临")
        break