Python Day 2 data type, character encoding, file processing

A primer

1 What is data?

　　x=10,10 is the data we want to store.

2 Why data is divided into different types

Data is used to represent States, and different States should be represented by different types of data.

3 Data types

Numbers (shaping, long-shaped, floating-point, plural)

String

BYTE string: Describes the byte bytes type when introducing character encoding

List

Meta-group

Dictionary

Collection

4 Expand Data Type learning by following several points

#一: Basic use 1 Purpose 2 definition way 3 common operation + built-in method # Two: The type Summary 1 to save a value or save multiple values can be stored in a value of multiple values, the value can be what type 2 ordered or unordered 3 variable or immutable!!! Variable: The value changes, the ID does not change. Variable = not hash!!! Immutable: The value changes, and the ID is changed. immutable = = can be hashed

Two numbers

Integral type and floating point type

#整型int role: Age, grade, social Security number, QQ number and other integer-related definitions: age=10 #本质age =int (Ten) #浮点型float role: salary, height, weight, physical parameters and other floating point salary=3000.3 #本质salary =float (3000.3) #二进制, decimal, octal, hex

Three strings

Name= values by index (positive fetch +

Four list

my_girl_friends=[,,, 4,5] =list (Access value by index (forward Access +

#ps: Reverse Step l=[1,2,3,4,5,6] #正向步长l [0:3:1] #[1, 2, 3] #反向步长l [2::-1] #[3, 2, 1] #列表翻转l [::-1] #[6, 5, 4, 3, 2, 1]

Five tuples

#作用: To save multiple values, the tuple is immutable (a key that can be used as a dictionary) in comparison to the list, primarily to read the # definition: Compared to a list type, except for [] age= (11,22,33,44,55) Nature age=tuple (11,22,33,44,55) #优先掌握的操作: Value by index (positive fetch + reverse): only slices (Gu Tou regardless of tail, step) length member operation in and not in loop

Six dictionaries

#作用: Save multiple values, Key-value access, fast value # Definition: Key must be immutable type, value can be any type info={' name ': ' Egon ', ' age ': ', ' sex ': ' Male '} #本质info =dict ({ ....}) or Info=dict (name= ' Egon ', age=18,sex= ' male ') or info=dict ([[' Name ', ' Egon '], (' age ', 18)]) or {}.fromkeys (' name ', ' age ', ' Sex '), None) #优先掌握的操作: Access Value by key: The available length Len member operation in and not in Delete key (), value values (), key value pair items () loop

Seven sets

# Role: de-weight, relational operations, #定义:             Knowledge points review               mutable types are non-hash types               immutable type is a hash type # definition set:              collection: Can contain multiple elements, separated by commas,             The elements of a collection follow three principles:              1: Each element must be an immutable type (hash , can be used as a dictionary key)              2: No duplicate elements               3: The purpose of a disorderly attention set is to store different values together, and to do relational operations between different sets. No need to tangle with a single value in the collection   #优先掌握的操作: Len member operation in and not in| collection & intersection-difference Set ^ symmetric difference set ==>,>= ,<,<=  parent set, subset 

Eight data Type Summary

Sub-footprint (low to high) per storage space

Numeric string collection: unordered, that is, unordered storage index related information tuple: ordered, need to store index related information, immutable list: Orderly, need to store index related information, variable, need to deal with the data to change the dictionary: unordered, need to save key and value mapping information, variable, need to deal with data deletion and modification

Differentiate by number of stored values

Scalar/Atomic Type	Number, string
Container type	list, tuple, dictionary

By Variable immutable distinction

Variable	List, dictionary
Not variable	Numbers, strings, tuples

Differentiate by Access order

direct access to	number
sequential access (sequence type)	String, list, tuple
key Value access (mapping type)	Dictionary

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Nine operators

#身份运算 (IS, isn't) is the ID, while the double equals is the value of the same, the ID is the same, and the same value is the same ID >>> x=1234567890>>> y=1234567890 >>> x = = ytrue>>> ID (x), id (y) (3581040, 31550448) >>> x is Yfalse

Python Day 2 data type, character encoding, file processing