effective python

Item 09-Never invoke virtual functions in constructors and destructors (never call virtual functions during construction or destruction)Why?Since the base class constructor executes earlier than the derived class constructor, the member variables of the base class constructor executing derived class have not been initialized. If the virtual function called during the period drops down to the derived class, it is necessary to know that the function of derived class will almost certainly take the

application that occupies the port, enter Tasklist|findstr "2748", such as , NB Sp , NB Sp , NB Sp , NB Sp , NB Sp NBS P , NB Sp nBsp Note: I here 5037 port is correct is occupied by Adb.exe, if it is you, is the other application End the process, enter taskkill/f/t/im your process name, such as Adb.exe, for example, when reconnecting your phone, you will find that

delete[in their destructor, so using auto_ptr or shared_ptr on a dynamically allocated array is a bad idea.Summarize:1. To prevent resource leaks, use the Raii object, which obtains resources in the constructor and releases resources in the destructor2. Two commonly used RAII classes are shared_ptr and Auto_ptr, the former being a better choice (both for managing resources on the heap) classlock{ Public: ExplicitLock (mutex*pm): mutexptr (PM) {mutexptr-Lock(); } ~Lock () {mutexptr-u

function is very powerful, but can not optimize JS. Because each function that invokes eval is guaranteed to be accessible to the Eval function at run time throughout the scope. You can use (0,eval) (SRC) to become an indirect call to improve performance. Other I don't think I need to know, after all, this would have been used less, at least I used less.Tips Wrapping the Eval function with a meaningless literal is wrapped in a sequence expression to achieve the purpose of forcing the u

-virtual functions specify interface inheritance and enforce inheritance. (as described in clause 33, do not hide non-virtual functions of the base class in a derived class in public inheritance)//Article 38: By compounding the mold out of the has-a or according to something to achieve//clause 39: Use private inheritance wisely and cautiously//1. Private inheritance is highly likely to be an orthodox design strategy when one of the classes needs to access the protected members of another class,

; result = * result + linenumber; return result; } */ //if an object is not constantly changing, and the cost is relatively large, you have to consider it. Hash code is cached inside the object//with volatile modifiers, the thread will read the variable's most-modified value each time it uses the variable. Private volatile inthashcode; @Override Public inthashcode () {intresult =hashcode; if(Result = = 0) {result= 17; Result= * result +AreaCode; Result= * result +prefix;

=typeof obj; if (!obj | | (t!== ' object ' t!== ' function ')) { throw new Error ("not an Object!) "); } return obj.__proto__;} }The above code determines whether the host environment implements the OBJECT.GETPROTOTYPEOF function and is safe in the ES5 standard environment.Tips Use standard-compliant object.getprototypeof functions instead of nonstandard __proto__ properties Implementing object.getprototypeof functions in non-ES5 environments t

LeetCode 36. Valid Sudoku (effective Sudoku) solution ideas and methodsValid SudokuDetermine if a Sudoku is valid, according to: Sudoku Puzzles-The Rules.The Sudoku board cocould be partially filled, where empty cells are filled with the character '.'.A partially filled sudoku which is valid.Note: A valid Sudoku board (partially filled) is not necessarily solvable. Only the filled cells need to be validated. Train of Thought: The question is very sim

Method 1: Add a variable to the/etc/profile file (valid for all users permanently)] Use VI to add a variable to the/etc/profile file. This variable will be valid for all users in Linux and will be "permanent ". To make the modification take effect immediately, run the following code # source/etc/profile method 2: In the user directory. add the variable "effective for a single user (permanent)" to the bash_profile file and use VI in the user directory.

1.info.plist file settings view controller-based status bar appearance value is no2. Add the following code to the APPDELEGATE.Mif ([[[[Uidevice Currentdevice] systemversion] Floatvalue] >= 7) { [application Setstatusbarstyle: Uistatusbarstylelightcontent]; Self.window.clipsToBounds =yes; Self.window.frame = CGRectMake (0,20,self.window.frame.size.width,self.window.frame.size.height-20); Self.window.bounds = CGRectMake (0, Self.window.frame.size.width, self.window.fr

virtual//Article 12: Do not forget every ingredient when copying an object//1. Copy all member variables of this class and call the appropriate copy function of its base class//2. The copy constructor is usually close to the work done by the copy assignment operator, but it is best not to let one call another, and a new function should be defined for the two functions to be called. //3. It is unreasonable to make the copy assignment operator call the copy constructor, because it is like trying

This problem may be of the greatest concern to many Java developers, especially new users. Now I will simply list some simple but effective methods: Reading other people's posts on various technical forums, especially those posts with a high number of replies or clicks, indicates that the discussion is intense, and it is likely that you are eager to discuss them, the high number of clicks indicates that you are very concerned about this. You may encou

structure, but it can be a bit difficult for people who don't understand the bind method.function curryingThe technique of binding a function to a subset of its parameters is called function curry (curring), which is named after the logic family, Haskell Curry.In comparison to explicit closed functions, the function of curry is a simple technique that uses fewer references to implement a function delegate.Personal understandingThe function is to curry, just the parameter processing, that is, si

compatible notation before ES5, please click to see more details.The following is the book on the tip of the content, remember a little bit to benefit a lot of OH.Tips Note that extracting a method does not bind the receiver of the method to the object of the method When passing an object method to a higher-order function, use an anonymous function to invoke the method on the appropriate receiver Use the Bind method to create a function bound to the appropriate receiver Ap

assumptions. In c++14, auto keyword can be used for function return value deduction, and for Lambda The formal parameter type declaration of an expression. In both of these usages, keyword implements the template type deduction rule instead of the auto type deduction rule, which is at this time the auto cannot be deduced as initializer_list : auto createinitlist () { return {1 , 2 , 3 }; // Auto deduces The return value and fails }std::vector int > V;auto Resetv = [

building closures-function expressions. function Sandwichmaker (magicingredient) { return function (filling) { Return magicingredient+ "and" +filling; } } Note that the function expression is anonymous. Because only a new value needs to be generated and not used locally, it is not necessary to name the function.Third fact: Closures can update the values of external variables.In fact, closures store references to external variables, not copies of their values. So an

undoubtedly valuable. And the number of calls to statements and functions can indirectly help you understand the behavior of software that cannot be measured directly. For example, if you cannot directly measure the use of dynamic memory, it is helpful to know how often the memory allocation function and the memory-release function are called. (i.e., operators New, new[], delete, and delete[]-see clause M8)Of course, even the best profiler is affected by the data it handles. If you profile your

, such as caching and prefething, is not contradictory to the advice I made in the clause M17 on lazy evaluation. When you have to support certain operations without always needing their results, lazy evaluation is the technique used at this time to improve program efficiency.over-eager is a technique used at this time to improve program efficiency when you have to support certain operations and their results are almost always needed or more than once. The huge performance improvements they prod

absolute to make it appear natural. Nav ul Li a:hover{Color: #06AEDA;}. Nav UL Li:hover ul {Display:block;Position:absolute;}Style All code:*{padding:0;margin:0;}. nav{width:100%;height:50px;Display:block;position:relative;}. Nav ul{Display:block;Float:right;position:relative;}. Nav ul li{Display:inline-block;padding:5px;Text-align:center;border-left:2px solid #f2f2f2;position:relative;}. Nav ul Li a{Color: #666;}. Nav ul Li ul{Display:none;}. Nav UL Li ul li{height:55px;width:50%;Border-left:n

value for all elements.I understand:All elements, for the judgment of the incoming function, have a false or false. It is true that all is true.Equivalent to all element execution functions after fetching and.[1,10,100].every(function(x){return x>5;});//false[1,10,100].every(function(x){return x>0;});//trueBoth of these methods are short-circuit loops. The subsequent loop is no longer executed as long as the resulting result can determine the final result. That is, once the some produces a true