01 variables
Variable is used to indicate or specify the name of a specific value, in Python variable assignment does not require type declaration, the assignment is created.
Variable naming rules:
1. The first letter or letters of the alphabet must underscore _ can not begin with a number
2. The remainder of the variables must consist of letters, numbers and underscore _ Composition
3. Variables are case sensitive
Use the equal sign (=) to assign values to variables. Equal sign (=) operator is a left variable name, an equal sign (=) operator is the right value stored in the variable. The figure is the number 666, 'data Phi Xia' are assigned to A, B variables.
Note: in python can be queried by the data structure type variable built-in function type ()
NOTE: A is numeric type, B is a string type
02 basic data structure type
There are six standard Python data structure type (extension package involve other types of data), the standard types of data structures are:
(1) Value Type
NOTE: A is a variable integer, B is a floating-point variables, C and D for the Boolean variables, E is a complex variable
(2) Type String
String enclosed in single quotation marks ( ') or double quotation mark ( "), and the string may use the plus (+) for splicing together, such as:
It is noted that when the intermediate string ends quotation marks also appeared, the need to add a backslash escape character before the intermediate quotation mark (\), such as:
Application: find the value of sin (Π / 2) and cos (Π / 3), as follows:
(3) the type of list
The list is written between square brackets ([]), by a comma (,) separated from the element, wherein the list can contain other type of data structure, as seen in FIG:
Square brackets (e.g., [0]) to the index values in the list, also possible to use square brackets (e.g. [2: 5]), taken in the form of a list of elements, the list of the index starting from 0, such as:
一般往列表中添加元素的函数为append()，使用方法如下：
修改元素用方括号索引的方式赋值，如：
删除元素直接用del函数删除索引出的元素，如：
（4）元组类型
元组有两种创建方法，一种是将一些值直接用逗号分开；另一种是用逗号分开并加上括号。注：元组不能像列表一样修改元素。如：
当元组只有一个值的时候要区分开元组和数值类型的不同，如代码中第一个为数值类型，第二个为元组类型。
（5）字典类型
字典由键和值组成，每个键与值用冒号（:）分隔，每一对键值对之间用逗号（,）分隔，同时将整个字典放在花括号内。如：
其他创建字典的方法：
（6）集合类型
使用大括号（{ }）或者set( )函数来创建集合，集合的作用很多时候可以用列表来代替，它的特点主要是可以用来删除重复元素，如下代码中1、2、3、4重复的元素只会出现一次：
03 数据类型相互转化
（1）数字与字符串的相互转化
（2）列表、元组、集合之间的相互转化
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（3）列表、元组、集合与字典的转化
将字典转化为列表、元组、集合只会保留其键，值不会保留，如：