Ⅰ. Operator(运算符)
1. Assignment operator (赋值运算符)
Simple assignment operators:

=

Compound assignment operators:

+=, -=, *=, /=

%=, **=, //=

2. Identifier (标识符)
a) An identifier is a name given to a variable, function, class or module.
b) be a combination of:
letters in lowercase (a to z) or uppercase (A to Z), 
numbers (0 to 9) ,
underscores( _ ).
c) must start with a letter or an underscore, and cannot start with a number !
d) cannot be “language reserved words” (keywords).

3. Arithmetic operators (算术运算符)

+,-,*,/

%  # remainder 取模(取余)
** # exponentiation 幂
// # floor division 取整

4.Comparison operators (比较运算符)

==,!=,>,<,>=,<=

5.Logical operators (逻辑运算符)

and &
or |
not

…………

Ⅱ. Basic data types
#type()

1. Boolean （布尔值）

Ture
False

2. Integer（整型）

3. Float （浮点数）
ⅰ) 取整
a.四舍五入

round()

eg.
b.向上/下取整

math.ceil()
math.floor()

eg.

ⅱ)Convert between int and float

int()
float()

4. String（字符串）
immutable  ordered

ⅰ) Basics
a.

 +.*

b.

in
not in

ⅱ) Built-in functions
a.

len()

b.
ⅲ) Index

str[]

ⅳ) Slicing

string_x [start: stop: step]

a) positions are inclusive at the start, but exclusive at the stop.
b) step can be specified to specify steps in slicing; the default value of step is 1.

ⅴ) String methods
# All string methods returns new values. They do not change the original string.
a) lower() ,upper()

string.lower() 
string.upper()

b> replace()

string.replace(oldvalue, newvalue, count)

c) count()

string.count(value, start, end)

d) find()

string.find(value, start, end)

e) split()

string.split(separator, maxsplit)

f) startswith(), endswith()

string.startswith(value, start, end) 
string.endswith(value, start, end)

g) strip()

string.strip(characters)

ⅵ) Conversion between data types

str()
int()
float()

Print formatting
1. Using the Modulo Operator: *%

‘d’ : *integer.
‘f’ or ‘F’ : Float.
‘s’ : String.

2. Using the format() function

3. Using f-Strings

Escape sequences (转义字符串)

\n – Newline (换行).

\t- Horizontal tab (Tab键/四个空格).

\r- Carriage return (回车符:将光标移到行首，覆盖等长的旧内容，超过新内容长度的旧内容部分会保留；不改变原内容).（常用于动态显示/更新进度）

\b- Backspace (退格删除).

\f- Form feed (换页符，很少用).

\'- Single Quote (单引号).

\"- double quote (双引号).

\\-Backslash (反斜杠).