小括号中优先运算
    a = 1
    b = 2
    c = 3
    ret = (a + b + c) / 3
    print(ret)

    print(10 / 3) # 正常除 #python2默认是底板除 10 / 3.0 就可保留小数部分
    print(10 // 3) # 地板除,舍弃小数部分
    print(10 % 3) # 取余数,取余/取模

    count = 0
    while count < 5:
    # count = count + 1 #count +=1
    # count = count - 1 #count -=1
    # count = count 1 #count =1
    # count = count / 1 #count /=1
    �