The set. Understanding the set () function. Class declaration in a separate file

Set () is an unordered collection with no duplicate items. However, I cannot figure out how it generates the result.

For example, consider the following:

Shouldn't set (y): set () output? I've tried these two in Python 2.6.

5 Solutions collect form web for “Understanding the set () Function”

As you say, the sets are unordered. While one way to implement collections is using a tree, they can also be implemented using a hash table (which means the keys in sorted order might not be so trivial).

If you want to sort them, you can simply do:

Sorted (set (y))

Otherwise, the only thing guaranteed by set is that it makes the elements unique (nothing more than once).

Hope this helps!

As the type of an unordered collection, set () is equivalent to set ().

Although it would be better to display the contents of the set in sorted order, which would make the repr () call more expensive.

Internally, the set type is implemented using a hash table: a hash function is used to split items into multiple buckets to reduce the number of equality operations required to check if an item is part of a set.

To create a repr () output, it simply outputs the items from each bucket in turn, which is unlikely to be ordered.

Like volatility and you pointed out, the sets are unordered. If you want the elements to be in order, just call sorted over the set:

>>> y = >>> sorted (set (y))

Python sets (and dictionaries) will iterate and print in some order, but exactly what will be in that order will be arbitrary and will not be guaranteed to remain the same after addition and removal.

Below is an example of changing the dialing order after adding a large number values ​​and subsequent deletion:

>>> s = set () >>> print (s) (8, 1, 6) >>> s.update (range (10,100000)) >>> for v in range (10, 100000): s .remove (v) >>> print (s) (1, 6, 8)

This is implementation dependent and therefore you should not rely on it.

I asked the same question today and got the answer to this answer. I still find it hard to understand why the set fails.

Mentioned this to my partner and he came up with this metaphor: take marble. You put them in a tube a little wider than the width of the marble: you have a list. The set, however, is a bag. Even if you feed the marble one by one into the bag; when you pour them from the bag back into the tube, they will not be in the same order (because they are all mixed up in the bag).

Classes and objects in C ++ are the main concepts of object-oriented programming - OOP. Object Oriented Programming is an extension of structured programming in which the basic concepts are the concepts of classes and objects. The main difference between the C ++ programming language and C is that there are no classes in C, and therefore the C language does not support OOP, unlike C ++.

To understand what classes are really needed for, let's draw an analogy with some object from Everyday life eg with a bicycle. A bicycle is an object that has been built according to blueprints. So, these same blueprints play the role of classes in OOP. Thus, classes are some descriptions, diagrams, drawings for which objects are created. It is now clear that to create an object in OOP, you must first draw up blueprints, that is, classes. Classes have their own functions, which are called class methods. The movement of the bicycle is carried out by rotating the pedals, if we consider the bicycle from the point of view of OOP, then the pedaling mechanism is a method of the class. Each bike has its own color, weight, different components - all these are properties. Moreover, for each created object, the properties may differ. Having one class, you can create an unlimited number of objects (bicycles), each of which will have the same set of methods, and you don't have to think about the internal implementation of the pedaling mechanism, wheels, braking system operation, since all this will already be defined in the class. Having dealt with the purpose of the class, we will give it a competent definition.

Classes in C ++ Is an abstraction that describes methods, properties, not yet existing objects. Objects- a specific representation of abstraction, which has its own properties and methods. Objects created based on one class are called instances of that class. These objects can have different behavior, properties, but they will still be objects of the same class. In OOP, there are three main principles for building classes:

1. Encapsulation Is a property that allows you to combine both data and methods working with them in a class and hide implementation details from the user.
2. Inheritance Is a property that allows you to create a new descendant class based on an existing one, while all the characteristics of the parent class are assigned to the descendant class.
3. Polymorphism- a property of classes that allows you to use objects of classes with the same interface without information about the type and internal structure of the object.

We'll go over each of the class building properties in detail as needed, but for now, just remember these three. Now back to the classes, first, let's look at the structure of the class declaration.

// class declaration in C ++ class / * class name * / (private: / * list of properties and methods for use inside the class * / public: / * list of methods available to other functions and program objects * / protected: / * list of tools available in inheritance * /);

A class declaration starts with a reserved keyword class followed by the name of the class. In curly brackets, lines 3 - 10 the body of the class is declared, and after the closing parenthesis it is necessary to put a semicolon, line 10... Three access specification labels are declared in the class body, lines 4, 6, 8, after each label, be sure to put a colon. V line 4 the access specifier label is declared private. All methods and properties of the class declared after the private access specifier will be available only inside the class. V line 6 Since the access specifier is public, all methods and properties of the class declared after the public access specifier will be available to other functions and objects in the program. For now, let's stop at this, we will not parse the protected access specifier now, just remember that it is. When declaring a class, it is not necessary to declare three access specifiers, and it is not necessary to declare them in that order. But it's better to immediately decide on the order of declaring access specifiers, and try to stick to it. Let's develop a program in which we will declare the simplest class in which one function will be declared that prints a message.

using namespace std; // start of class declaration class CppStudio // class name (public: // access specifier void message () // function (class method) displaying a message on the screen (cout<< "website: сайт\ntheme: Classes and Objects in C + +\n"; } }; // конец объявления класса CppStudio int main(int argc, char* argv) { CppStudio objMessage; // объявление объекта objMessage.message(); // вызов функции класса message system("pause"); return 0; }

V lines 7 - 14 we have defined a class named CppStudio... It is customary to start a class name with a capital letter; subsequent words in the name must also begin with a capital letter. This combination of letters is called camel register, since the alternation of large and small letters resembles the silhouette of a camel. The class body declares the public access specifier, which allows other functions to call the class methods declared after public. That is why, in the main function, in line 19 we were able to call the message () function. In class CppStudio only one function is declared, which has no parameters and displays a message on the screen, the line 12 ... Class methods are the same functions, only they are declared inside the class, so everything related to functions is relevant for class methods as well. The declaration of classes is carried out in the same way as the declaration of functions, that is, the class can be declared in a separate file or in the main file, we will see later how this is done. V line 18 the objMessage variable of the CppStudio type is declared, and so, the objMessage variable is an object of the CppStudio class. Thus, the class is a complex data type. After the class object is declared, you can use its methods. There is only one method - the message () function. To do this, refer to the method of the objMessage object through a dot, as shown in line 19, as a result the program will display a text message (see Figure 1).

Website: theme website: Classes and Objects in C ++

Figure 1 - Classes in C ++

set - functions and get - class functions

Each object has its own properties or attributes that characterize it throughout its life. Object attributes are stored in variables declared within the class that owns the object. Moreover, the declaration of variables must be performed with the access specifier private. Such variables are called items. Since the data items are declared private, only class methods can access them, external access to the data items is prohibited. Therefore, it is customary to declare special methods in classes - the so-called set and get functions, with which you can manipulate data elements. set functions initialize data items, get functions allow you to view the values ​​of the data items. Let's modify the CppStudio class so that it can store the date in the format dd.mm.yy... To change and view the date, we implement the set and get functions, respectively.

// classes.cpp: defines the entry point for the console application. #include "stdafx.h" #include using namespace std; class CppStudio // class name (private: // access specifier private int day, // day month, // month year; // year public: // access specifier public void message () // function (class method) displaying a message to the screen (cout<< "\nwebsite: сайтntheme: Classes and Objects in C + +\n"; } void setDate(int date_day, int date_month, int date_year) // установка даты в формате дд.мм.гг { day = date_day; // инициализация день month = date_month; // инициализация месяц year = date_year; // инициализация год } void getDate() // отобразить текущую дату { cout << "Date: " << day << "." << month << "." << year << endl; } }; // конец объявления класса CppStudio int main(int argc, char* argv) { setlocale(LC_ALL, "rus"); // установка локали int day, month, year; cout << "Введите текущий день месяц и год!\n"; cout << "день: "; cin >> day; cout<< "месяц: "; cin >> month; cout<< "год: "; cin >> year; CppStudio objCppstudio; // object declaration objCppstudio.message (); // call the function of the message class objCppstudio.setDate (day, month, year); // initialize the date objCppstudio.getDate (); // display the date system ("pause"); return 0; )

A new private access specifier appeared in the class definition, line 9... This access specifier restricts access to variables that are declared after it and before the start of the public access specifier, lines 9 - 12... Thus, only class methods can access the variables day, month, year. Functions not belonging to the class cannot access these variables. Data members or class methods that are declared after the private access specifier but before the next access specifier start are called private data members and private methods of the class. Following the principle of least privilege and the principle of good programming, it is advisable to declare data members after the access specifier private, and class methods after the public access specifier. Then, to manipulate data elements, special functions are declared - get and set. We added two methods setDate () and getDate () to the CppStudio class, we will take a closer look at each method. SetDate () method is defined with 18 to 23 lines... As previously mentioned, set - functions initialize data items, so the setDate () method does just that. That is, the setDate () method initializes the variables day, month, year. To view the values ​​in private data items, the getDate () function is declared, which returns the values ​​from the variables day, month, year as a date. This concludes the class definition, in main (), as always, we create an object of the class, and through the object we call its methods, lines 39 - 41... If the data items were declared after the public specifier, we could refer to them in the same way as to the methods of the class. The result of the program is shown in Figure 2.

Enter the current day, month and year! day: 10 month: 11 year: 2011 website: sitentheme: Classes and Objects in C + + Date: 11/10/2011

Figure 2 - Classes in C ++

Constructors

In the previous program, the CppStudio class declared data items that can store date information. When the class object was created, we first called set - function, in order to set the current date (thereby initializing data items), and then called get - function and saw the corresponding date on the screen. If we first called get - function, then instead of the date we would see some numbers - garbage. So, when creating objects, you can immediately initialize the data members of the class, the constructor performs this function. Constructor- a special function that performs the initial initialization of data elements, and the name of the constructor must necessarily coincide with the name of the class. An important difference between the constructor and other functions is that it does not return any values ​​at all, including void. Any class must have a constructor, even if the constructor is not explicitly declared (as in the previous class), then the compiler provides a default constructor, without parameters. Let's modify the CppStudio class by adding a constructor to it.

// classes.cpp: defines the entry point for the console application. #include "stdafx.h" #include << "\nwebsite: сайт\ntheme: Classes and Objects in C + +\n"; } void setDate(int date_day, int date_month, int date_year) // установка даты в формате дд.мм.гг { day = date_day; // инициализация день month = date_month; // инициализация месяц year = date_year; // инициализация год } void getDate() // отобразить текущую дату { cout << "date: " << day << "." << month << "." << year << endl; } }; // конец объявления класса CppStudio int main(int argc, char* argv) { CppStudio objCppstudio(11,11,2011); // объявление объекта и инициализация элементов данных objCppstudio.message(); // вызов функции message objCppstudio.getDate(); // отобразить дату system("pause"); return 0; }

// code Code :: Blocks

// Dev-C ++ code

// classes.cpp: defines the entry point for the console application. #include using namespace std; class CppStudio // class name (private: // access specifier private int day, // day month, // month year; // year public: // access specifier public CppStudio (int date_day, int date_month, int date_year) // class constructor (setDate (date_day, date_month, date_year); // call the function for setting the date) void message () // function (class method) displaying a message on the screen (cout<< "\nwebsite: сайт\ntheme: Classes and Objects in C + +\n"; } void setDate(int date_day, int date_month, int date_year) // установка даты в формате дд.мм.гг { day = date_day; // инициализация день month = date_month; // инициализация месяц year = date_year; // инициализация год } void getDate() // отобразить текущую дату { cout << "date: " << day << "." << month << "." << year << endl; } }; // конец объявления класса CppStudio int main(int argc, char* argv) { CppStudio objCppstudio(11,11,2011); // объявление объекта и инициализация элементов данных objCppstudio.message(); // вызов функции message objCppstudio.getDate(); // отобразить дату return 0; }

The constructor is declared in lines 13 - 16... The constructor has three parameters through which it receives information about the date, in the body of the constructor it is called set - function to set the date. It was possible to implement the initial initialization of class data members without set - functions, but since this function was provided, it would be more correct to use this particular function, line 15... V line 35 we declare an object of the class, and after the name of the object in parentheses, we pass three arguments. This is how the initial initialization of data items is performed using the constructor (see Figure 3).

Website: theme website: Classes and Objects in C + + date: 11/11/2011

Figure 3 - Classes in C ++

Class declaration in a separate file

Until now, the class declaration was performed in the file with the main function and everything worked. Suppose you need to write a program, for this you need to use the CppStudio class - the class we developed earlier. To use this class, you need to include the file in which it is declared. As we have already said, files are included using the #include preprocessing directive. But even if we can connect the file with the class, a new problem will appear - since the file with the class already contains the main () function, the compiler will generate an error when building the project. The essence of the error: “Several main () were found in the project - functions. " That is why the class must be declared in a separate file so that it can be used repeatedly. Earlier we declared functions in a separate file, in the same way the class is placed in a separate file. To do this, you need to follow 3 steps:

1. declare a custom class in the header file, in our case - CppStudio ;
2. connect the header file to the program, in our case - #include "CppStudio.h".

Depending on the development environment, the methods for adding files to the project may differ, but the essence of the task remains the same. In MVS2010, a header file can be added by calling the context menu (right-click) in “ solution explorer"By selecting the item" create a new item". In the dialog box that appears, select the file type we need — this is * .h and fill in the field “ File name". As before, we choose a meaningful name, as a rule, the same as the name of the class. Now a new header file has been added to our project - CppStudio.h.

In the newly created header file, declare a class and, if necessary, include additional headers. Here's what should have happened:

// header file CppStudio.h #include using namespace std; // class declaration class CppStudio // class name (private: // access specifier private int day, // day month, // month year; // year public: // access specifier public CppStudio (int date_day, int date_month, int date_year) // class constructor (setDate (date_day, date_month, date_year); // call the function for setting the date) void message () // function (class method) displaying a message on the screen (cout<< "nwebsite: сайтntheme: Classes and Objects in C + +n"; } void setDate(int date_day, int date_month, int date_year) // установка даты в формате дд.мм.гг { day = date_day; // инициализация день month = date_month; // инициализация месяц year = date_year; // инициализация год } void getDate() // отобразить текущую дату { cout << "date: " << day << "." << month << "." << year << endl; } }; // конец объявления класса CppStudio

In order for the main function to see the class we have created and to be able to use it, it is necessary to include the class definition in the executable file, with the main () function. This is done like this:

// code Code :: Blocks

// Dev-C ++ code

// classes.cpp: defines the entry point for the console application. // include the CppStudio class #include "CppStudio.h" int main (int argc, char * argv) (CppStudio objCppstudio (11,11,2011); // object declaration and initialization of data items objCppstudio.message (); // call functions message objCppstudio.getDate (); // display the date system ("pause"); return 0;)

V line 5 the definition of the CppStudio class is connected, only after that you can create objects of the class, use its methods, etc. The result of the program is exactly the same as before, only the structure of the project has changed.

Separating interface from implementation

Class interface- a construct that defines the methods and properties provided by the class. Class implementation Is a way of making the class work. Before that, we did not separate the interface of the class from its implementation, that is, the implementation of the methods was carried out inside the class. The separation of the interface from the implementation of the class is done in order to hide the way the class works. Separating the interface from the implementation is done in 5 steps:

1. add the header file * .h to the project;
2. define class interface in header file
3. add an executable file * .cpp to the project;
4. execute the implementation of the class in the executable file;
5. connect the header file to the program.

We already know how to add the header file to the project, the executable file is also added in the same way, the names of these files are given, as a rule, the same. The class interface should look like this:

// class header file СppStudio.h // class interface // class declaration class CppStudio // class name (private: // access specifier private int day, // day month, // month year; // year public: // access specifier public CppStudio (int, int, int); // class constructor void message (); // function (class method) displaying a message on the screen void setDate (int, int, int); // setting the date in dd format. mm.yy void getDate (); // display the current date); // end of CppStudio class declaration

Declared variables and prototypes of class methods remain in the class interface. Now let's look at the contents of the class methods implementation file.

// class implementation file CppStudio.cpp #include using namespace std; // connect the class interface to its implementation file #include "CppStudio.h" CppStudio :: CppStudio (int date_day, int date_month, int date_year) // class constructor (setDate (date_day, date_month, date_year); // call the function for setting the date ) void CppStudio :: message () // function (class method) displaying a message on the screen (cout<< "nwebsite: сайтntheme: Classes and Objects in C + +n"; } void CppStudio::setDate(int date_day, int date_month, int date_year) // установка даты в формате дд.мм.гг { day = date_day; // инициализация день month = date_month; // инициализация месяц year = date_year; // инициализация год } void CppStudio::getDate() // отобразить текущую дату { cout << "date: " << day << "." << month << "." << year << endl; }

To link the interface of a class and its implementation, you need to connect the header file with the class definition in the implementation file, line 6(highlighted line). After that, you can declare the class methods. Class methods are declared in the same way as functions, only before the method name, you must write the class name and put the unary operation of resolving the scope " :: «.

// syntax for declaring class methods outside the class body / * return data type * / / * class name * / :: / * method name * / (/ * method parameters * /) (// operators)

Since the methods of the class are declared outside the body of the class, it is necessary to associate the implementation of the method with the class, and for this we will use the binary operation of resolving the scope. The binary scoping operation binds an externally declared method to a class that has the same name as the method declaration. This is why it is necessary to add the class name and the scope resolution operation in the declaration of a class method.

So, the class interface is defined, the class methods are declared, it remains to connect the header file in the executable file with the main () function and the program is ready.

// classes.cpp: defines the entry point for the console application. #include "stdafx.h" // include the CppStudio class #include "CppStudio.h" int main (int argc, char * argv) (CppStudio objCppstudio (11,11,2011); // object declaration and initialization of data items objCppstudio. message (); // call the message function objCppstudio.getDate (); // display the date system ("pause"); return 0;)

// code Code :: Blocks

// Dev-C ++ code

// classes.cpp: defines the entry point for the console application. // include the CppStudio class #include "CppStudio.h" int main (int argc, char * argv) (CppStudio objCppstudio (11,11,2011); // object declaration and initialization of data items objCppstudio.message (); // call functions message objCppstudio.getDate (); // display the date return 0;)

V line 5 we include the class header file, after which we can create objects of this class.

A few tips on how to shape the interface of the future class and what to do or not to do.

One of the most frequently requested features of Windows 10 by users is the ability to create separate tabs in the standard Explorer (over 20K votes). After introducing tabs in Internet Explorer 6 through a special extension back in 2005, Microsoft has long resisted the idea of ​​adding tabs in Explorer or any other application, but very soon the situation will change to the opposite. The software giant will indeed allow tabs to be created in any Windows 10 application. The functionality is called Sets.

In the coming weeks, select Windows Insider beta testers will be able to try it out. At the same time, the developers have not yet named the specific dates for the availability of functionality for all users of Windows 10.

Note that this functionality became known for the first time back in April. At that time, the function was tentatively titled Tabbed Shell.

Initially, Sets functionality will only work with Universal Apps built on the Universal Windows Platform (UWP). Developers expect to collect as much feedback and recommendation as possible before implementing any improvements. However, in the future, it is likely that Sets will not be limited to UWP apps alone, but will support traditional Win32 / x86 desktop programs as well.

The idea behind Sets is fully reflected in the name. The functionality allows you to create sets of tabs related to the performance of a particular task. Working with a document in Word, for example, the user begins to search for research results and other data on the topic on the network or use his own sketches from notes. So, for convenience, he can combine all the applications used for a specific project in one window. The Sets function allows you to switch between different aspects of the application, strictly separating everything by task.

Microsoft has big plans for Sets, which extend well beyond the Windows 10 desktop OS. Similar to Timeline, another interesting Windows 10 functionality that should be available to testers in the next test build of Windows 10, Sets will allow you to work with applications by getting them access from various devices. That is, it will be possible to start work on one PC, and then resume from the same place where it left off, on any other PC or smartphone. The official video below allows you to visualize the capabilities of the Sets function:

Perhaps the hardest part for Microsoft will be to get the right support from third-party developers. Surely, for the first time, the functionality of Sets will be limited to the Office suite, File Explorer, Notepad and Edge browser.

Externally, Sets looks the same as an empty Microsoft Edge tab. The function also supports universal search.

And Microsoft's drive to integrate Microsoft Edge into all Windows 10 apps raises some questions. Moreover, the software giant has already been "burned" because of this approach. Back in 2001, the US Department of Justice began a lawsuit with Microsoft over the latter's decision to embed Internet Explorer directly into Windows. However, the market has changed a lot during this time. Plus, without the functionality of a web browser, this tab interface is meaningless.

Again, Microsoft will begin testing the Sets functionality with a limited number of testers in the coming weeks. The developers want to hear the first feedback before starting full-scale testing.