MODERNISATION  OF  HIGHER  EDUCATION  
                                       IN  CENTRAL  ASIA  
                                 THROUGH  NEW  TECHNOLOGIES  
                                         ( HiEdTec ) 
             
             
                            Object Oriented Programming 
                               Lecture2: Defining variables 
             
                In programming, a variable is a value that can change, depending on the 
            conditions or on information passed to the program. Typically, a program consists 
            of instruction s that tell the computer what to do and data that the program uses when 
            it is running. The data consists of constants or fixed values that never change and 
            variable values (which are usually initialized to "0" or some default value because 
            the actual values will be supplied by a user's program). Usually, both constants and 
            variables are defined as certain data type s. Each data type prescribes and limits the 
            form of the data. Examples of data types include: an integer expressed as a decimal 
            number, or a string of text characters, usually limited in length. 
                Variables are used to store information to be referenced and manipulated in a 
            computer program. They also provide a way of labeling data with a descriptive 
            name, so our programs can be understood more clearly by the reader and ourselves. 
            It is helpful to think of variables as containers that hold information. Their sole 
            purpose is to label and store data in memory. This data can then be used throughout 
            your program. 
            Assigning Value to Variables 
                Naming variables is known as one of the most difficult tasks in computer 
            programming. When you are naming variables, think hard about the names. Try 
            your best to make sure that the name you assign your variable is accurately 
            descriptive and understandable to another reader. Sometimes that other reader is 
            yourself when you revisit a program that you wrote months or even years earlier. 
            When you assign a variable, you use the = symbol. The name of the variable goes 
            on the left and the value you want to store in the variable goes on the right. 
             
            Creating Variables 
            Variables are containers for storing data values. 
            Unlike other programming languages, Python has no command for declaring a 
            variable. 
            A variable is created the moment you first assign a value to it. 
                                                             MODERNISATION  OF  HIGHER  EDUCATION  
                                                                               IN  CENTRAL  ASIA  
                                                                    THROUGH  NEW  TECHNOLOGIES  
                                                                                    ( HiEdTec ) 
                         
                        Example 
                        x = 5 
                        y = "Sapartach" 
                        print(x) 
                        print(y) 
                        Variables do not need to be declared with any particular type and can even change 
                        type after they have been set. 
                        Example 
                        x = 4 # x is of type int 
                        x = "Sally" # x is now of type str 
                        print(x) 
                        String variables can be declared either by using single or double quotes: 
                        Example 
                        x = "Sapartach" 
                        # is the same as 
                        x = 'Sapartach' 
                        Variable Names 
                        A variable can have a short name (like x and y) or a more descriptive name (age, 
                        car name, total volume). Rules for Python variables: 
                                 A variable name must start with a letter or the underscore character 
                                 A variable name cannot start with a number 
                                 A variable name can only contain alpha-numeric characters and underscores 
                                  (A-z, 0-9, and _ ) 
                                 Variable names are case-sensitive (age, Age and AGE are three different 
                                  variables) 
                        Example 
                        #Legal variable names:                           
                        myvar = " Sapartach " 
                        my_var = " Sapartach " 
                                             MODERNISATION  OF  HIGHER  EDUCATION  
                                                          IN  CENTRAL  ASIA  
                                                  THROUGH  NEW  TECHNOLOGIES  
                                                             ( HiEdTec ) 
                 
                _my_var = " Sapartach" 
                myVar = "Sapartach " 
                MYVAR = "Sapartach " 
                myvar2 = "Sapartach " 
                 
                #Illegal variable names:          
                2myvar = "Sapartach" 
                my-var = "Sapartach " 
                my var = "Sapartach " 
                Remember that variable names are case-sensitive 
                Assign Value to Multiple Variables  
                Python allows you to assign values to multiple variables in one line: 
                Example 
                x, y, z = "Orange", "Banana", "Cherry" 
                print(x) 
                print(y) 
                print(z) 
                And you can assign the same value to multiple variables in one line: 
                Example 
                x = y = z = "Orange" 
                print(x) 
                print(y) 
                print(z) 
                 
                 
                 
                 
                 
                 
                 
                 
                 
                 
                 
                           MODERNISATION  OF  HIGHER  EDUCATION  
                                   IN  CENTRAL  ASIA  
                              THROUGH  NEW  TECHNOLOGIES  
                                    ( HiEdTec ) 
            
            
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