Python 1:
Python course syllabus:
Class 1: Intro+Variable
Class 2: Condition+Loop execution
Class 3: Data type- string, integer, list, tuple
Class 4: Function&class+ Data type-dictionary
Class 5: reading and writing files
一. Python environment
Jupyter notebook（本地）
Colab: Google cloud based（云端，需要google account）
二. Variable
1. Constants: fixed values such as numbers, letters, and strings are called "constants"(常量)，because their value does not change.
Numeric constants are as you expect; String constants（一般指字母） use single quotes(') or double quotes(")(数字不加引号，字母可加单引号或双引号)
2. Variables: a variable is a named place in the memory where a programmer can store data and later retrieve the data using the variable "name".
Programmers get to choose the names of the variables. You can change the contents of a variable in a later statement.
3. Python Variable Name Rules:
Must start with a letter or underscore_，如：spam egg spam23 _speed, 如果这样写23spam #sign var.12，python读不出来（variable里不能有点，#或空格等字符）
Must consist of letters and numbers and underscores
Case Sensitive：大小写不一样，记录的variable也不一样
4. Reserved Words（python内设词）: you cannot use reserved words as variable names/identifiers(python系统内部已设置好的variable，是无法复制的，但如果把首字母改成大写，也是可以在这类词附加变量值，但一般不这么操作，以免出现confusion)，如：and，del，for，is，raise，assert，elif，from，lambda，return，break，else，global，not，try，class，except，if，or，while，continue，exec，import，pass，yield，def，finally，in，print，as，with
5. Sentences or Lines展示
x = 2（assign 2给 x）
x = x+2 或 x += 2（replace x的值等于原x+2 ）
print x （return x的结果）
x是variable，=和+是operator，2是constant，print是reserved word
6. Numeric Expressions
because of the lack of mathematical symbols on computer keyboards, we use "computer-speak" to express the classic math operations, 如：**代表power（指数，2 ** 3 = 8），%代表 remainder（余数）
7. Operator Precedence Rules
Highest precedence rule to lowest precedence rule(由高到低):
Parenthesis are always respected
Exponentiation
Multiplication, DIvision, and Remainder
Addition and Subtraction
Left to right
8. Type: in Python variables, literals and constants have a "type". Python knows the difference between an integer number and a string.(data type必须相同，才能做相关的operation, 可以数字+数字，字符+字符，不能数字+字符或字符+数字)
9. Several Types of Numbers: two main types
Integers are whole numbers, 如：-14，-2，0，1，100，401233
Floating Pointing Numbers have decimal parts, 如：-2.5，0.0，98.6，14.0
There are other number types- they are variations on float and integer
10. Type Conversions:
Integer conversions-When you put an integer and floating point in an expression, the integer is implicitly converted to a float, you can control this with the built-in functions int() and float().
String conversions-You can also use int() and float() to convert between strings and integers. You will get an error if the string does not contain numeric characters.(数字可以通过int（）和float（）把包含数字的string转换成数字，或把数字转换成string，但不能把不含任何数字的string转换成数字)
11. User Input: We can instruct Python to pause and read data from the user using the raw_input() function. The raw_input() function returns a string.
12. Comments in Python:
Anything after a # is ignored by Python.
Why comment- describe what is going to happen in a sequence of code; document who wrote the code or other ancillary information; turn off a line of code perhaps temporarily
13. String Operations
some operators apply to strings, 如 + implies “concatenation”，print 'abc' + '123' returns abc123；* implies "multiple concatenation", print 'Hi' * 5 returns HiHiHiHiHi
Python knows when it is dealing with a string or a number and behaves appropriately
