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# 声明一个列表nums = [['a1', 'a2', 'a3'], ['b1', 'b2', 'b3']]# 参数为list数组时，是压缩数据，相当于zip()函数iters = zip(*nums) # 输出zip(*zipped)函数返回对象的类型# print("type of iters is %s" % type(iters))# 因为zip(*zipped)函数返回一个zip类型对象，所以我们需要对其进行转换# 在这里，我们将其转换为列表print(list(ite..

axis是将矩阵进行分组原始矩阵的shape=[3,4,5]，取axis=0再进行操作后，得到的矩阵shape=[4,5]。取axis=1再进行操作后，得到的矩阵shape=[3,5]。取axis=-1（axis=2）再操作后，shape=[3,4]。掌握这一点，能有利于你在神经网络中的变换或是数据操作中明确矩阵变换前后的形状...

目的：While pass by value is suitable in many cases, it has a couple of limitations. First, when passing a large struct or class to a function, pass by value will make a copy of the argument into the function parameter. In many cases, this is a needless per

Classesare an expanded concept ofdata structures: like data structures, they can contain data members, but they can also contain functions as members.class class_name { access_specifier_1: member1; access_specifier_2: member2; ...} ob...

Type aliases (typedef / using)In C++, any valid type can be aliased so that it can be referred to with a different identifier.//using new_type_name = existing_type ;using C = char;using WORD = unsigned int;using pChar = char *;using field = char.

Data structuresAdata structureis a group of data elements grouped together under one name. These data elements, known asmembers, can have different types and different lengths. Data structures can be declared in C++ using the following syntax:struc...

In the programs seen in previous chapters, all memory needs were determined before program execution by defining the variables needed. But there may be cases where the memory needs of a program can only be determined during runtime. For example, when the m

Address-of operator (&)The address of a variable can be obtained by preceding the name of a variable with an ampersand sign (&), known asaddress-of operator. For example:int *foo;foo = &myvar; //foo 必须是个指针，才能存&This would assign t..

*p++ // same as *(p++): increment pointer, and dereference unincremented address*++p // same as *(++p): increment pointer, and dereference incremented address++*p // same as ++(*p): dereference pointer, and increment the value it points to(*p)++ .

A typical declaration for an array in C++ is:type name [elements];wheretypeis a valid type (such asint,float...),nameis a valid identifier and theelementsfield (which is always enclosed in square brackets[]), specifies the length of the array i...

Namespaces allow us to group named entities that otherwise would haveglobal scopeinto narrower scopes, giving themnamespace scope. This allows organizing the elements of programs into different logical scopes referred to by names.namespace identifier...

Defining a function template follows the same syntax as a regular function, except that it is preceded by thetemplatekeyword and a series of template parameters enclosed in angle-brackets <>:template <template-parameters> function-declarati..

inline functionCalling a function generally causes a certain overhead (stacking arguments, jumps, etc...), and thus for very short functions, it may be more efficient to simply insert the code of the function where it is called, instead of performing the

string concatenate (string a, string b){ return a+b;}This function takes two strings as parameters (by value), and returns the result of concatenating them. By passing the arguments by value, the function forcesaandbto be copies of the arguments...

The syntax shown above for functions:type name ( argument1, argument2 ...) { statements }Requires the declaration to begin with a type. This is the type of the value returned by the function. But what if the function does not need to return a value? In th

// passing parameters by reference#include <iostream>using namespace std;void duplicate (int& a, int& b, int& c){ a*=2; b*=2; c*=2;}int main (){ int x=1, y=3, z=7; duplicate (x, y, z); cout << "x=" << x &.

The standard header<sstream>defines a type calledstringstreamthat allows a string to be treated as a stream, and thus allowing extraction or insertion operations from/to strings in the same way as they are performed oncinandcout. This feature ...

1，命名空间的using声明作用域操作符（::）编译器应从操作符左侧名字所示的作用域中寻找右侧那个名字。std::cin的意思就是要使用mingmingko

1.可寻址的最小内存块称为“字节（byte）”2. 存储的基本单元称为“字（word）”

import shutilimport osfile_path = '你的绝对路径'def divide_files(file_path, sub_file_num):#sub_file_num 是 你想要分成几个文件夹 name = os.listdir(file_path) name_num = len(name) each_file_num = int(name_num/sub_file_num) #我的文件内容是成对的（img,xml) 所以不能出现奇数.

#include<iostream>#include "Sales_item.h"int main(){ Sales_item total, book; std::cout << "请输入几个ISBN相同的书籍" << std::endl; if (std::cin >> total) { while (std::cin >> book) { if (compareIsbn(total, book)) { tot.

#include<iostream>int main(){ int sum = 0, value = 0; while (std::cin >> value) { sum += value; } std::cout << sum << std::endl; std::cin.get();}

#results是一个TEXT：大概长这样 ('[[1,2,3,4# 5,6,7,8]]')for each in results: each = each[0] print(each) each = each.replace('[','').replace(']','').replace('\n',' ') print(each) tokens = each.split() print(to.

Table:-- Select clients that have an invoiceSELECT *FROM clients cWHERE EXISTS( SELECT client_id FROM invoices WHERE client_id = c.client_id)output:

--Select employees whose salary is above the average in their office-- GET invoices that are larger than the client's average invoice amountSELECT *FROM invoices iWHERE invoice_total > ( SELECT AVG(invoice_total) FROM invoices WHERE clien

--Select client with at least two invoices__________________________________________count___________________________________________________看一下COUNT的用法：SELECT client_id, COUNT(*)FROM invoicesGROUP BY client_idOutput：_________________________

-- Select invoices larger than all invoices of client 3USE sql_invoicing;SELECT *FROM invoicesWHERE invoice_total >( SELECT MAX(invoice_total) FROM invoices WHERE invoice_id = 3)Other solution(with ALL 关键字)：USE sql_invoicing;SELEC

-- Find customers who have ordered lettuce(id = 3)-- Select customer_id, first_name, last_nameSELECT *FROM customers-- 在下面的子查询中， 返回订购了生菜的顾客的IDWHERE customer_id IN ( SELECT o.customer_id FROM order_items oi JOIN orders o USING(orde...

-- Find the products that have never been orderedUSE sql_store;SELECT *FROM productsWHERE product_id NOT IN( SELECT DISTINCT product_id FROM order_items)Output：-------------------------------------------------------------------作业---.

-- FIND products that are more-- expensive than Lettuce(id = 3)SELECT *FROM productsWHERE unit_price > ( SELECT unit_price FROM products WHERE product_id = 3)-- (这里面是lettuce的价格)Output：-------------------------------------------.

SELECT pm.name AS payment_method, sum(amount) AS totalFROM payments p JOIN payment_methods pm ON p.payment_method = pm.payment_method_idGROUP BY pm.name WITH ROLLUPOutput:

SELECT client_id, SUM(invoice_total) AS total_salesFROM invoicesGROUP BY client_id -- 分组HAVING total_sales > 500-- 使用having子句：为了在分组之后进行筛选Output:-------------------------------------------------作业-----------------------------------..

SELECT client_id, SUM(invoice_total) AS total_salesFROM invoicesWHERE invoice_date >= '2019-07-01'GROUP BY client_id -- 看每一个顾客花的钱ORDER BY total_sales DESC -- 按照total_sales 的降序来显示 看看谁花的多-- 注意顺序 永远是 FROM WHERE GROUP_BY ORDER_BY 这个顺序哈Ou.