Python Learning notes (ii)

Directory:

I. Lists, tuples

Two. String

Three. Dictionaries, collections

Four. Conditional judgment and circulation

I. Lists, tuples

a data type built into Python. Lists: List, an ordered set of elements that can be added and removed at any time.

Cases:

>>>players = ['Lebron'Kobe'Kyrie  ']>>>players['Lebron' Kobe ' ' Kyrie ']

The variable players is a list.

Get the number of list elements with the Len () function:

>>>len (players)

3

An index is used to access the elements of each position in the list, starting at 0, and getting the last element can be indexed by-1.

Slice:

>>>players = ['Lebron','Kobe','Kyrie','Dwyane']>>>players[1:3]#Remove the number between the Mark 1-3, including 1, not including 3['Kobe','Kyrie']>>>PLAYERS[1:-1]#Remove the value labeled 1 to-1, excluding -1['Kobe','Kyrie']>>>players[:3]#starting from scratch, 0 can be ignored['Lebron','Kobe','Kyrie']>>>players[2:]#take from the last start['Kyrie','Dwyane']>>>players[0:0:2]#the next 2 represents every other element to take a['Lebron','Kyrie']>>>PLAYERS[::2]#same as the previous sentence.['Lebron','Kyrie']

Additional:

Players.append ()

Insert:

>>>players = ['Lebron','Kobe','Kyrie','Dwyane','Chris']>>>players.insert (2,'Kevin')>>>players['Lebron','Kobe','Kevin','Kyrie','Dwyane','Chris']

View Code

Modify:

players[2]= ' SC '

Delete:

>>>del players[2]>>>players.remove ('Kobe'#  Delete the specified element # Delete the last value of the list

Extended:

>>>players['Lebron','Kobe','Kyrie','Dwyane']>>>b = [1, 2, 3]>>>Players.extend (b)>>>players['Lebron','Kobe','Kyrie','Dwyane', 1, 2, 3]

Copy:

P_copy = Players.copy ()

Follow-up supplement

Statistics:players.count (' Lebron ')

Sort:players.sort () #Python3 different types cannot be sorted together

Invert:players.reverse ()

get subscript:Players.index ()

Tuples: Once created, cannot be modified.

Players = (' Lebron ', ' Kobe ', Kyrie ')

There are only two methods: Count,index

Two. String

Method:

Name.capitalize () #首字母大写

Name.casefold () #大写全部变小写

Name.center ("-") #输出 '----------Lebron----------'

Name.count (' a ') #统计a出现的次数

Name.encode () #将字符串编码成byte格式

Name.endswith ("a") #判断字符串是否以a结尾

"Bryce\tyang". Expendtabs (10) Output ' Bryce Yang ', convert \ t to spaces

Name.find (' a ') #查找a, found to return its index, could not find return-1

Format

>>>stu = "My name is {}, age is {}"

>>>stu.format ("Allen", 18)

' My name is Allen,age is 18 '

>>>stu = "My name is {1}, age is {0}"

>>>stu.format ("Allen", 18)

' My name is ' and ' is Allen '

>>>stu = "My name is {name} ', age was {age}"

>>>stu.format (age=18, name= "Allen")

' My name is Allen,age is 18 '

Format_map

>>>stu.format_map ({' name ': ' Allen ', ' Age ': 18})

' My name is Allen,age is 18 '

Names.isalnum () #字符串中是否只包含字母和数字

Names.isalpha () #是否只包含字母, kanji

#是否是数字

Names.isdecimal ()

Names.isdigit () #三种的区别

Names.isnumeric ()

#将字符串中的每一个元素按照指定分隔符进行拼接

Test = "everything"

v = "_". Join (Test)

Names.lower () #转为小写

Names.upper () #转为大写

Names.lstrip () #去除左空白

Names.rstrip () #去除右空白

Names.strip () #去除左右空白

Three. Dictionaries, collections

The dictionary uses a key-value (Key-value) store, which has a very fast lookup speed.

Grammar:

>>>d = {'Michael'Bob'Tracy ': >>>d['Michael']95

Compared to list, Dict has the following features:

1. The search and insertion speed is very fast and will not slow with the increase of key;

2. It takes a lot of memory and a lot of wasted memory.

The key in the dictionary is an immutable object, so strings, integers, and so on can be key, and list is mutable and cannot be a key.

Dictionaries are unordered.

Collection (SET):

>>>s = set ([+])

>>>s

{A-i}

Set can be regarded as a set of mathematical unordered and non-repeating elements, so that two sets can do the intersection and set of mathematical meanings.

Four. Conditional judgment and circulation

If...else

Age =If age>18:    print('your-is ', age)     Print('adult')else:      Print(' YourAge was', age)    print(' teenager ')

Elif is an abbreviation for else if

if< condition judgment;:

< execution >

elif< condition judgment 2>:

< execution >

elif< condition judgment 3>:

< Executive 3>

Else

< Executive 4>

For loop:

names = ['Michael'Bob'Tracy ' ] for in names:    print(name)

While loop:

sum == while n > 0:    = sum+n    = n-2print(sum)

Break exits the loop prematurely:

n = 1 while n<=100:    if n >10:        break     Print(n)    = n+1print('END')

Continue skips the current loop and starts the next loop directly:

n = 0 while n<10:    = n+1    if n%2 = =0        :Continue    Print(n)

Python Learning notes (ii)