Python data operations, dictionaries, lists

Constant definition rule: constant meaning is not changed; Constant definition name is all uppercase;

such as: mysql_connection= ' 192.168.1.1 '

Pyc:python generated translation files that enable the computer to recognize the Python language;

Syntax and use of the list:

List parameter insertion syntax: Name.insert (2, ' Minggou ')

NAME[1] = "Wangminglong"---> Modify the contents of the corresponding field in the list;

Append: Name.append ("Alex")

Delete: Name.remove ("Minggou")

Definition list: name=["1", "Minghu", 2,43, "Minggou"]

Step: Print (Name[::2]) every other place value once;

Query list: which in name

If 9 in Name:

Num_of_ele = Name.count (9)

Position_of_ele = Name.index (9)

Name[position_of_ele] = 999

Print ("[%s] 9 is in name,postion:[%s]"% (Num_of_ele,position_of_ele))

Print (name)

For I in Range (Name.count (9)): #修改所有9

Ele_index = Name.index (9)

Name[ele_index] = 9999999

Print (name)

List Merge:

Name.extend (name2)

List inversion:

Name.reverse ()

List sort:

Name.sort () #字符串和数字结合排序, Python3 will be an error, separate row will not error

Enter the subscript to delete the element and delete the last one by default:

Name.pop ()

Copy the list, copy only the first layer, do not copy the second layer, the second layer copies the memory data sharing:

Name.copy ()

List nesting:

name = ["CSD", "Asvs", [2,3,56,7], "CDC", 354]

View List Length:

Print ("Name", Len (name))

Read-only list:

R = (1,2,3,4,5) #不想被改动的列表, read-only list, tuple;

String Common operations:

name = "Qiu Ye"

Username = input ("Name:")

If Username.strip () = = ' Qiuye ': #移除空格;

Print ("Welcome")

String segmentation:

names = "Dwqd,ascd,frer"

name2 = Names.split (",")

Print (name2) #变为列表

Print ("|". Join (name2)) #按 | to split the output;

String index:

name = "Qiu Ye"

Print ("in name) #判断字符串中是否有空格

Print (Name.capitalize ()) #首个字母大写

Name.format () #字符串格式化

Cases:

msg = "Hello,{name},it ' The {age} last time ..."

MSG2 = Msg.format (name= ' Minghu ', age=333)

Print (MSG2)

MSG2 = "Hh{0},ddas{1}"

Print (Msg2.format ("Alex", 33))

Slices: Slice with same list

name = "Alex Li"

Print (Name[2:4])

Print (Name.center, '-') #40个字符居中打印, other bytes used-instead;

Print (Name.find ()) #指定字段查找并输出;

Judge:

age = Int (input ("Your Age:"))

If Age.isdigit (): #判断是否为数字

age = Int (age)

Else

Print ("Invalid data type")

Name.isalnum () #不能包含特殊字符

Name.endswith () #判断结束

Name.startswith () #判断开始

Name.upper () #大写

Name.lower () #小写

Data operations:

Type ("333") is Str

Type (a) is List

Binary representation:

256 128 64 32 16 8 4 2 1

0 0 0 0 0 0 0 0 0

1 1 1 1 1 1 1 1 1

The smallest unit that can be represented in a computer is a bits;

The smallest unit that can be stored in a computer is a bits (bit)

8bit = byte (bytes)

1024byte = 1 KByte

1204kbyte = 1mbyte

1024MB =1GB

Operator:

<< Right Shift

>> left Shift

Cases:

64>>2 = = 16

64<<1 = = 128

Python dead Loop:

Cases:

Count = 0

While True:

Print ("This is true", count)

Count +=1

Dictionary:

id_db ={

1248357148965: {#key值必须是唯一的, otherwise only the last one is output;

' Name ': ' Shanpao ', #name: Dictionary key, ' Shanpao ': Key's value

' Age ': ' 24 '

' Addr ': ' Dongbei '

}，

1248357448965: {

' Name ': "Shanpao",

' Age ': ' 24 '

' Addr ': ' Dongbei '

}，

124835712345: {

' Name ': "Shanpao",

' Age ': ' 24 '

' Addr ': ' Dongbei '

}，

}

#字典的基本格式, the storage information is more flexible;

Assign a new value to key:

id_db[1248357448965][' name '] = "new value" #修改value;

id_db[1248357448965][' qq_of_wife ' = 123556675 #如果字典中没有此value, the new value is added;

Print (Id_db.setdefault (234254364), "HHH")) #取一个默认值, if not present, assigns a new value;

Print (Dict.fromkeys ([1,2,34,5,6,8], ' DDD ')) #将列表中每个值拿出来当做场景使用---> A pit!

Id_db.popitem () #随机删除字典中的一个key---> recommends not to use any random language;

High-efficiency loops:

For key in id_db:

Print (Key,id_db[key])

Example: Shopping Cart

salary =  () Salary.isdigit ():    salary =  (Salary):      () Welcome_msg = .center (,) (welcome_msg) exit_flag =product_list = [      (,),     (,),     (,),     (,),      (,),     (,),     (,),]shop_car = []    exit_flag :     (. Center (,))     item  (product_ List):        index = item[]         p_name = item[][]        p_price =  item[][]         (Index,,p_name,p_price)      user_choice =  ()     user_choice.isdigit (): user_choice =  (user_ Choice)         user_choice <  (product_list):             p_item = product_list[user_choice]             p_item[] <= salary:  shop_car.append (P_item)    salary -= p_item[]  (% (p_item,salary))              :                  (% salary)     :        user_ choice == user_choice == :              (. Center (,))             item shop _car:                 (item)              (. Center (,))               (% salary)             exit_ flag = user_choice == user_choice == :              (. Center (,))              item shop_car:                  (item)              (. Center (,))               (% salary)

Python data operations, dictionaries, lists