Class notes for Introduction Python_week 3 and 4

1. in Canvas, the origin is always on upper-left corner.
2. On a 300 by 200 pixel canvas, the pixel coordinates range from 0, 0 in the top left to 299, 199 in the bottom right.

3.draw handler needs to be registered.
4. use Brackets [], to define the position of the texts.  The position is the lower-left corner of the string.

5. print s1[0]  是从0开始数一个string， 第一个字母是第0个。
6. print s1[-1] 是print 最后一个字母。
7. print s1[0:7] 是print 前7个字母，不包括7所代表的的那个字母，是开区间。
8. s2[:13] 前13位。

9. str（123）把 数字变成string；  int()就是string转成整数

10. position = [50, 60]      position[0] = 50     position[1] = 60

11. decomposition the program is important. draw is draw, timer is timer, message is message. One has nothing to do with another.

12. don't forget start the frame.   frame.start() . same for timer.   timer1.start()  timer2.start()

WEEK 4

1. list   [] empty list;  [1,2,3] or ['hello', 'goodbye'];  position = [4, 9]; even other list inside list.
 [[1,3], ['a', 'b'], []]

2. len() return the length of the list.

3.  access the list print l[0]    index start from 0   .   l2[1:3] 是l2里的第二项和第三项，不包裹第四项。

4. l2[0] = 'cheese'

5. chr() turns the key codes number into caracter.

6. in Python power use ** 2  it is square

7. In python, for update vector, we need update x and y separately.

8. a is a list, and b = a,  if change a element in a,       b is changed too.

9. a is a list,   b = list(a) , b is the same list as a , but when updating a ,   b unchanged.

10. In a function , we do not need "global" if using mutation. We only need it when doing assignment.

11. type([1,2,3]) is list,     type((1,2,3)) is tuple.  tuple is not mutable.  If you want to protect your data, you'd better save it as a tuple.

Class notes for Introduction Python_week 1 and 2

1. variable name: only start with  "_" or letters. Not start with number. 也最好不要用点 . 在中间
2. "=" assign; "==" logical comparison.
3. update variable:  my_age +=1.   take the current variable value and plus 1 as new variable value.
4." : " 意味着下面要写一个block of codes. 下面的要indent,几个indent没关系，重要的是一致。when the indent is done, the block of codes is done.
5. function does not have a parameter. In this case, no input, function return NONE.

6. -3%800   结果是 797
7.  35//10，是把35除以10，然后取小数点前面剩下的数
8. str(aaa) + str(bbb) +"1111" 是把这三个string 都连起来。
9.  if        elif         else
10 在 function 里面解释， 用三个连续的 双引号“”“在前， 也用三个”“” 在后。叫做documentation。 解释这个方程式做什么的。  用comment也行。

11. x += y + x  意思是 x=x+y 然后再加上x。   和 x=x+y 意思不同。

if  condition:
   result
elif  condition:
   result
else:
   result

要写 x ==1 or x == 2,    不能 x ==1 or 2

WEEK TWO

1. Events : Input; Keyboard; Mouse; Timer
2. there is a event queue in Python which we cannot see. event一个一个的执行，不能两个一起执行。如果同时出发两个事件（比如点鼠标和按键盘），python会形成一个Queue，一个一个执行。
3. 当event发生的时候，python 会去执行相对应的Handler.

4. all the variables created inside a function are called Local variables, it can only be used in the function.
5.如果在function 里定义一个和外面的variable一样名字的variable。在function里面按你定义的走，但是外面的不影响。

6. 挡在一个function里面要创建或调用一个global variable的话，就写出来  global number1

7. Program Structure： 1. Globals (State); 2. Helper Functions ;3 . Classes(Later)
          4. Define event handlers; 5. create a frame; 6. register event handlers. 7. start frame & timers

8.  simple gui 里面是里面 string input(text input)， 要用 function  int() 转换成integer number 或者用float（） 来转换成floating point number.

9. 当写一个方程，没有说return什么东西的话。python会return NONE。 因为Python总是要return一个东西。

10. 写方程的时候，在每一步都加上print的输入和输出的东西，会是很好的debug工具。 最好还能加上lable