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The hasattr() method in PythonThe hasattr() method returns true if an object has the given named attribute and false if it does not.SyntaxThe syntax of hasattr() method is −hasattr(object, name)The hasattr() is called by getattr() to check to see if AttributeError is to be raised or not.The hasattr() method takes two parameters −The hasattr() method returns −True, if object has the given named attributeFalse, if object has no given named attributeExampleclass Male: age = 21 name = 'x' x = Male() print('Male has age?:', hasattr(x, 'age')) print('Male has salary?:', hasattr(x, 'salary'))OutputThis gives the output('Male has age?:', ... Read More
Python getattr()The getattr() method returns the value of the named attribute of an object. If not found, it returns the default value provided to the function.SyntaxThe syntax of getattr() method is −getattr(object, name[, default])The getattr() method can take multiple parameters −The getattr() method returns −value of the named attribute of the given objectdefault, if no named attribute is foundAttributeError exception, if named attribute is not found and default is not definedExampleclass Male: age = 21 name = "Abel" x = Male() print('The age is:', getattr(x, "age")) print('The age is:', x.age)OutputThis gives the output('The age is:', 21) ... Read More
Class variables vs Instance VariablesAll variables outside the class __init__ function in Python are class variables while those inside the same are instance variables. The difference between the class variables and instance variables is understood better by examining the code belowExampleclass MyClass: stat_elem = 456 def __init__(self): self.object_elem = 789 c1 = MyClass() c2 = MyClass() # Initial values of both elements >>> print c1.stat_elem, c1.object_elem 456 789 >>> print c2.stat_elem, c2.object_elem 456 789 # Let's try changing the static element MyClass.static_elem = 888 >>> print c1.stat_elem, c1.object_elem 888 789 >>> print ... Read More
On re-declaring a variable in JavaScript, the variable value still remains the same.ExampleLet’s see an example. Here, we are declaring the variable age −
The following is stated about declaration and initialization of a variable in ECMAScript specification −A var statement declares variables that are scoped to the running execution context’s VariableEnvironment. Var variables are created when their containing Lexical Environment is instantiated and are initialized to undefined when created. [...] A variable defined by a VariableDeclaration with an Initializer is assigned the value of its Initializer’s AssignmentExpression when the VariableDeclaration is executed, not when the variable is created.The above defines the difference:All variables are initialized with the value undefined.Variables declarations are initialized with undefined upon the initialization of their lexical environment.This initialization does ... Read More
selfThe word 'self' is used to represent the instance of a class. By using the "self" keyword we access the attributes and methods of the class in python.__init__ method"__init__" is a reseved method in python classes. It is called as a constructor in object oriented terminology. This method is called when an object is created from a class and it allows the class to initialize the attributes of the class.ExampleFind out the cost of a rectangular field with breadth(b=120), length(l=160). It costs x (2000) rupees per 1 square unitclass Rectangle: def __init__(self, length, breadth, unit_cost=0): self.length ... Read More
The instantiation or calling-a-class-object operation creates an empty object. Many classes like to create objects with instances with a specific initial state. Therefore a class may define a special method named __init__(), as follows −def __init__(self) − self.data = [ ]When a class defines an __init__() method, class instantiation automatically invokes the newly-created class instance which is obtained by −x = MyClass()The __init__() method may have arguments. In such a case, arguments given to the class instantiation operator are passed on to __init__(). For example, >>> class Complex: ... def __init__(self, realpart, imagpart): ... ... Read More
To check if a variable exists in JavaScript, you need to check it against null as in the following code. Here, we’re checking the existence of variable myVar − var myVar = 20; if(myVar !== undefined && myVar !== null) { document.write("Variable exists"); }
Before you use a variable in a JavaScript program, you must declare it. Variables can be thought of as named containers. You can place data into these containers and then refer to the data simply by naming the container.Variables are declared with the var keyword as follows. You can also declare multiple variables with the same var keyword as follows − This is also you can assign values −var rank = 2; var points = 100;
The Boolean object represents two values, either "true" or "false". If value parameter is omitted or is 0, -0, null, false, NaN, undefined, or the empty string (""), the object has an initial value of false.The new Boolean() is used to create a new object. Use the following syntax to create a boolean object.var val = new Boolean(value);ExampleLet us see an example of toString() method, which returns a string of either "true" or "false" depending upon the value of the object − JavaScript toString() Method var flag = new Boolean(false); document.write( "flag.toString = " + flag.toString() );