Write code to explicitly verify that each entry is distinct from the other, and that each entry is an instance of the Dummy class. Then, create a tuple that contains a single instance of Dummy stored ten times.
Write code to explicitly verify that the entries all reference the exact same object, and that each entry is an instance of the Dummy class. Reading Comprehension: Terminology. What relationship do x and Cat share? What relationship do y and Cat share? What relationship do x and y share? What relationship do x2 and y share? What relationship do y and y1 share?
Next, identify each of the following objects as a class object or an instance and if instance, an instance of what. Now that we know the basics of how to create an instance of a class, understand the relationship between class objects and instances, and understand the distinction between instances that are independent from one another, we can move on to learning about creating instance-level attributes for our class.
This is a critically-important method, which we will leverage often. Consider the slightly-modified definition of Person , which also includes the class-attribute x :. This first argument, self , actually represents the object instance of Person that is being created.
The resulting object does not yet have a name attribute. It only has the class-level attribute x. With these arguments, Person. Is this true , please see the above answer by user is it correct or not? So that's what the term "instance" really means: it describes a relationship not a thing. Stephen C Stephen C k 90 90 gold badges silver badges bronze badges. I really appreciate your answer sir, and I almost got it, just one more question.
We say-"Whenever the compiler hits the 0 argument constructor it creates a instance of a class. In this context what is really created an instance or an object? An object I guess and we use the word "instance" as synonym. But it would kind, if you better confirm it. Ryan: Basically yes: it is creating an Object which is an instance of the Class in question. But note that the quoted sentence is saying "instance of a Class" rather than just "instance" RuneFS - the "modelling" I am talking about is not about representation.
It is theoretical. Yea, in some languages there are objects that denote types, or even that allow you to enumerate all of the instances of a type.
But those properties augment the generic "modelling" rather than invalidating it. RuneFS - No I am talking about "type theory". It is a branch of mathematics. It is independent of the technology that is used to run programs. The closest type theory gets to computation is lambda calculus. If you are interested, try and get hold of a copy of "Types and Programming Languages" by Benjamin C.
You are making the same mistake as user You are treating variables as "names". They are not. Variables are "reference holders" that contain references to objects. Objects don't have intrinsic names. The references are the closest thing that there is to a "name" for an object, except that they don't have a constant representation. The GC can move an object which changes the bit pattern used to represent the reference.
Show 9 more comments. When a class is declared, no memory is allocated so class is just a template. When the object of the class is declared, memory is allocated. DevD 57 1 1 silver badge 13 13 bronze badges. Did you mean that objects and instances are same?
Thanks david for the link. From the topics I got this Every real world things which have state and behaviour can be called as "object". And to classify these objects we use class A class is the blueprint from which individual objects are created. And it says that, the objects of the class are instances.
Now please someone tell me what is the differences between object and instance? Does this mean that object don't really exist in context of programming and instance represents object in it? And you'll find that the JLS does not define the term 'instance' at all. See my answer. Ryan: See my answer for the distinction between "instance" and "object". Mustafa's answer and comment are IMO misleading. Memory is allocated to at least represent the static variables of the class. And for other things too that are related to the type identity of the class.
Shreshth Kharbanda 1, 12 12 silver badges 20 20 bronze badges. Class is Data Type,You use this type to create object. Instance is Logical but object is Physical means occupies some memory. Object is instance of class and instance means representative of class i. Instance refers to Reference of an object. Object is actually pointing to memory address of that instance.
Lucky SwatiKothari SwatiKothari 3 3 silver badges 8 8 bronze badges. Arun Arun 2, 6 6 gold badges 24 24 silver badges 40 40 bronze badges. Honestly, I feel more comfortable with Alfred blog definitions: Object : real world objects shares 2 main characteristics, state and behavior.
Carlos Casallas Carlos Casallas 3 3 silver badges 9 9 bronze badges. Abishek M Abishek M 51 7 7 bronze badges. Objects in the real world are physical. Objects in a computer program are not physical. You can't touch them.
They don't obey the laws of physics. And even the bit patterns in memory are representations of objects So Car is a class that can represent any real world car someCar is an instance of the Car class and someCare represents one real life object your car however instance and object is very often used interchangably when it comes to discussing coding.
Strictly speaking someCar is a reference to a Car instance. The instance itself doesn't have a name. Kage Kage 1 1 gold badge 3 3 silver badges 9 9 bronze badges. Class It has logical existence, i. It is a set of objects. A class may be regarded as a blueprint to create objects. This is usually used to the benefit of the program, since aliases behave like pointers in some respects. For example, passing an object is cheap since only a pointer is passed by the implementation; and if a function modifies an object passed as an argument, the caller will see the change — this eliminates the need for two different argument passing mechanisms as in Pascal.
Incidentally, knowledge about this subject is useful for any advanced Python programmer. A namespace is a mapping from names to objects.
Examples of namespaces are: the set of built-in names containing functions such as abs , and built-in exception names ; the global names in a module; and the local names in a function invocation.
In a sense the set of attributes of an object also form a namespace. The important thing to know about namespaces is that there is absolutely no relation between names in different namespaces; for instance, two different modules may both define a function maximize without confusion — users of the modules must prefix it with the module name.
By the way, I use the word attribute for any name following a dot — for example, in the expression z. Strictly speaking, references to names in modules are attribute references: in the expression modname. Attributes may be read-only or writable. In the latter case, assignment to attributes is possible. Module attributes are writable: you can write modname.
Writable attributes may also be deleted with the del statement. For example, del modname. Namespaces are created at different moments and have different lifetimes. The namespace containing the built-in names is created when the Python interpreter starts up, and is never deleted. The global namespace for a module is created when the module definition is read in; normally, module namespaces also last until the interpreter quits.
The built-in names actually also live in a module; this is called builtins. The local namespace for a function is created when the function is called, and deleted when the function returns or raises an exception that is not handled within the function. Actually, forgetting would be a better way to describe what actually happens. Of course, recursive invocations each have their own local namespace.
A scope is a textual region of a Python program where a namespace is directly accessible. Although scopes are determined statically, they are used dynamically. At any time during execution, there are 3 or 4 nested scopes whose namespaces are directly accessible:. To rebind variables found outside of the innermost scope, the nonlocal statement can be used; if not declared nonlocal, those variables are read-only an attempt to write to such a variable will simply create a new local variable in the innermost scope, leaving the identically named outer variable unchanged.
Usually, the local scope references the local names of the textually current function. Class definitions place yet another namespace in the local scope.
In fact, local variables are already determined statically. A special quirk of Python is that — if no global or nonlocal statement is in effect — assignments to names always go into the innermost scope. Assignments do not copy data — they just bind names to objects. The same is true for deletions: the statement del x removes the binding of x from the namespace referenced by the local scope.
In fact, all operations that introduce new names use the local scope: in particular, import statements and function definitions bind the module or function name in the local scope. The global statement can be used to indicate that particular variables live in the global scope and should be rebound there; the nonlocal statement indicates that particular variables live in an enclosing scope and should be rebound there.
This is an example demonstrating how to reference the different scopes and namespaces, and how global and nonlocal affect variable binding:. You can also see that there was no previous binding for spam before the global assignment. Class definitions, like function definitions def statements must be executed before they have any effect.
You could conceivably place a class definition in a branch of an if statement, or inside a function. The function definitions inside a class normally have a peculiar form of argument list, dictated by the calling conventions for methods — again, this is explained later. When a class definition is entered, a new namespace is created, and used as the local scope — thus, all assignments to local variables go into this new namespace.
In particular, function definitions bind the name of the new function here. When a class definition is left normally via the end , a class object is created. The original local scope the one in effect just before the class definition was entered is reinstated, and the class object is bound here to the class name given in the class definition header ClassName in the example.
Attribute references use the standard syntax used for all attribute references in Python: obj. So, if the class definition looked like this:. Class attributes can also be assigned to, so you can change the value of MyClass. Class instantiation uses function notation.
Just pretend that the class object is a parameterless function that returns a new instance of the class. For example assuming the above class :. Many classes like to create objects with instances customized to a specific initial state.
So in this example, a new, initialized instance can be obtained by:. For example,. Now what can we do with instance objects? The only operations understood by instance objects are attribute references. There are two kinds of valid attribute names: data attributes and methods. Data attributes need not be declared; like local variables, they spring into existence when they are first assigned to.
For example, if x is the instance of MyClass created above, the following piece of code will print the value 16 , without leaving a trace:. The other kind of instance attribute reference is a method.
In Python, the term method is not unique to class instances: other object types can have methods as well. For example, list objects have methods called append, insert, remove, sort, and so on. Valid method names of an instance object depend on its class. By definition, all attributes of a class that are function objects define corresponding methods of its instances.
So in our example, x. But x. In the MyClass example, this will return the string 'hello world'. However, it is not necessary to call a method right away: x. For example:. What exactly happens when a method is called?
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