老师，书上讲到有另外的状态：等待状态（waiting）、计时等待状态（timed waiting）。这两种状态有什么区别吗？

老师的方法：

select job_id,sum(salary),sum(decode(department_id,20,salary))"Dep20",sum(decode(department_id,50,salary))"Dep50",sum(decode(department_id,80,salary))"Dep80" ,sum(decode(department_id,90,salary))"Dep 90"from employees group by job_id order by sum(salary);

结果：

我的方法：

select job_id, sum(salary), decode(department_id, 20, sum(salary)), decode(department_id, 50, sum(salary)), decode(department_id, 80, sum(salary)), decode(department_id, 90, sum(salary)) from employees e group by job_id, department_id order by sum(salary);

结果：

我与老师的区别是：

        老师是sum里面放decode，后面不用加department_id的分组

        我的是decode里面放sum，后面需要加department_id的分组

两组结果的区别是

                        我的返回的是20个结果，

                        老师返回的是19个结果

这两个的区别我没有搞清楚，老师可以解惑一下么？

请问安装mysqlclient只是为了简化命令python manage.py吗？我在操作时，更改了DATABASES中的内容时就会提示：Did you install mysqlclient or MySQL-python?

执行安装mysqlclient命令（视频中pip3 install mysqlclient，为什么是pip3，我试了pip install mysqlclient，好像效果都一样，没能安装成功，提示的错误也一样，如下：）

(venv) D:\PycharmProjects\zhuce>pip3 install mysqlclient

Collecting mysqlclient

  Using cached https://files.pythonhosted.org/packages/f4/f1/3bb6f64ca7a429729413e6556b7ba5976df06019a5245a43d36032f1061e/mysqlclient-1.4.2.post

1.tar.gz

Installing collected packages: mysqlclient

  Running setup.py install for mysqlclient ... error

    Complete output from command D:\PycharmProjects\zhuce\venv\Scripts\python.exe -u -c "import setuptools, tokenize;__file__='C:\\Users\\ThinkP

ad\\AppData\\Local\\Temp\\pip-install-a58bcz2e\\mysqlclient\\setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n',

 '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record C:\Users\ThinkPad\AppData\Local\Temp\pip-record-j4b8_u4b\install-record

.txt --single-version-externally-managed --compile --install-headers D:\PycharmProjects\zhuce\venv\include\site\python3.6\mysqlclient:

    C:\Users\ThinkPad\AppData\Local\Programs\Python\Python36-32\lib\distutils\dist.py:261: UserWarning: Unknown distribution option: 'long_descr

iption_content_type'

      warnings.warn(msg)

    running install

    running build

    running build_py

    creating build

    creating build\lib.win32-3.6

    creating build\lib.win32-3.6\MySQLdb

    copying MySQLdb\__init__.py -> build\lib.win32-3.6\MySQLdb

    copying MySQLdb\_exceptions.py -> build\lib.win32-3.6\MySQLdb

    copying MySQLdb\compat.py -> build\lib.win32-3.6\MySQLdb

    copying MySQLdb\connections.py -> build\lib.win32-3.6\MySQLdb

    copying MySQLdb\converters.py -> build\lib.win32-3.6\MySQLdb

    copying MySQLdb\cursors.py -> build\lib.win32-3.6\MySQLdb

    copying MySQLdb\release.py -> build\lib.win32-3.6\MySQLdb

    copying MySQLdb\times.py -> build\lib.win32-3.6\MySQLdb

    creating build\lib.win32-3.6\MySQLdb\constants

    copying MySQLdb\constants\__init__.py -> build\lib.win32-3.6\MySQLdb\constants

    copying MySQLdb\constants\CLIENT.py -> build\lib.win32-3.6\MySQLdb\constants

    copying MySQLdb\constants\CR.py -> build\lib.win32-3.6\MySQLdb\constants

    copying MySQLdb\constants\ER.py -> build\lib.win32-3.6\MySQLdb\constants

    copying MySQLdb\constants\FIELD_TYPE.py -> build\lib.win32-3.6\MySQLdb\constants

    copying MySQLdb\constants\FLAG.py -> build\lib.win32-3.6\MySQLdb\constants

    running build_ext

    building 'MySQLdb._mysql' extension

    error: Microsoft Visual C++ 14.0 is required. Get it with "Microsoft Visual C++ Build Tools": http://landinghub.visualstudio.com/visual-cpp-

build-tools

    ----------------------------------------

Command "D:\PycharmProjects\zhuce\venv\Scripts\python.exe -u -c "import setuptools, tokenize;__file__='C:\\Users\\ThinkPad\\AppData\\Local\\Temp

\\pip-install-a58bcz2e\\mysqlclient\\setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(co

mpile(code, __file__, 'exec'))" install --record C:\Users\ThinkPad\AppData\Local\Temp\pip-record-j4b8_u4b\install-record.txt --single-version-ex

ternally-managed --compile --install-headers D:\PycharmProjects\zhuce\venv\include\site\python3.6\mysqlclient" failed with error code 1 in C:\Us

ers\ThinkPad\AppData\Local\Temp\pip-install-a58bcz2e\mysqlclient\

You are using pip version 10.0.1, however version 19.1.1 is available.

You should consider upgrading via the 'python -m pip install --upgrade pip' command.

已经按照格式书写了，为什么还是会有异常呢？

class ComputerFactory:
    x=None
    y=True

    def __new__(cls, *args, **kwargs):
        if ComputerFactory.x==None:
            ComputerFactory.x=object.__new__(cls)
        return ComputerFactory.x

    def __init__(self):
        if ComputerFactory.y:
            print("just one factory")
        ComputerFactory.y=False
    def create_computer(self,brand):
        if brand=="联想":
            return lenovo()
        if brand=="华硕":
            return asus()
        if brand=="神州":
            return hasee()

        print("finish creating")


class computer:
    screen="liquid crystal"
    keyboard=True
    def caculate(self):
        print("Make computer")


class lenovo(computer):
    def caculate(self):
        print("Lenovo")

class asus(computer):
    def caculate(self):
        print("ASUS")

class hasee(computer):
    def caculate(self):
        print("Hasee")

C1=ComputerFactory().create_computer("联想")
C2=ComputerFactory().create_computer("华硕")
C3=ComputerFactory().create_computer("神州")
print(C1,C2,C3)

老师，代码末尾几行，如果说写成C1=ComputerFactory.create_computer("联想"),就是类ComputerFactory后没加括号，python报错说需要两个参数 这是为什么？

老师，我现在遇到一个问题，我在命名函数时，一旦命名为test开头的函数名后，前面会自动变成测试的状态，运行结果也跟平常状态不一样了。视频里不会出现这种情况，怎么解决？

print(type(str))
print(type(dict))
print(type(int))
print(type(list))
print(type(tuple))
print(type(set))
def test():
    pass
class Person():
    def run(self):
        pass
a = Person()
c = a.run
print(type(test))
print(type(c))
print(type(function))
print(type(method))

二、运行结果

三、疑问

老师你好，请问6个基本数据类型的模具类是type .python中一切都是对象，type 类实例化了所类，所有类继承与object类，用type方法 查看方法和函数的类型却报错了，他们不是type类的实例吗，

老师我是在icon下载下来的但是找不动demo_unicode.html这个东西？

字节流中的read(byte[] b)和read(byte[] b,int off,int len)他俩都是读取到数组当中去，read(byte[] b)没有指定off和len，read(byte[] int off,int len)中为什么要具体指出off和len，他俩区别在哪里，怎么却别理解？

老师，原来不是说main方法是程序的执行入口，在这个里面main方法创建的对象是一个空值，那他是如何执行出线面显示的语句呢？

cursor.execute(sql)

这条语句是干嘛的呢 老师

还有3306的端口号是不是不能换了 3306是怎么得出来的 

老师的数据库那几个权限表的sql语句有吗？

public class TestStringBuilder2 {
	public static void main(String[] args) {
		StringBuilder sb = new StringBuilder();//实际上创建了一个长度为16的char类型的数组
		StringBuilder sb2 = new StringBuilder("hello");//5+16
		sb2.append("world");
		sb2.append("world");
		sb2.append("world");
		sb2.append("world");
		
		System.out.println(sb2);
		System.out.println("容量" + sb2.capacity() + "\tsb2的长度" + sb2.length());
	}

}

问题：视频中所说的超过字符数组下标就会扩容，然后扩容是用长度*2+2，但到底是怎样算数组的下标什么时候扩容呢？能解释一下吗？

汉化后的Developer导出的文件导入到英文版的Developer中会不会出现乱码的情况

老师我的运行结果怎么这样？系统太随意了么？跟你的咋不一样?

import threading,time
num = 0
def work1():
    global num
    for i in range(100):
        num +=1
        print("in work1,num is %d"%num)
def work2():
    global num
    for i in range(100):
        num +=1
        print("in work2,num is %d"%num)
t1 = threading.Thread(target=work1)
t1.start()
t2 = threading.Thread(target=work2)
t2.start()
print("计算之后num=",num)