Bound, unbound, and static methods in Python
Methods in Python are like functions except that it is attached to an object.The methods are called on objects and it possibly make changes to that object. These methods can be Bound, Unbound or Static method. The static methods are one of the types of Unbound method. These types are explained in detail below.
If a function is an attribute of class and it is accessed via the instances, they are called bound methods. A bound method is one that has ‘
self‘ as its first argument. Since these are dependent on the instance of classes, these are also known as instance methods.
Need for these bound methods
The methods inside the classes would take at least one argument. To make them zero-argument methods, ‘
decorators‘ has to be used. Different instances of a class have different values associated with them.
For example, if there is a class “Fruits”, and instances like apple, orange, mango are possible. Each instance may have different size, color, taste, and nutrients in it. Thus to alter any value for a specific instance, the method must have ‘self’ as an argument that allows it to alter only its property.
My name is A from object 1 My name is B from object 2 My name is C from object 2 My name is A from object 1
In the above example two instances namely samp1 and samp2 are created. Note that when the function
alterIt() is applied to the second instance, only that particular instance’s value is changed. The line samp1.myFunc() will be expanded as sample.myFunc(samp1). For this method no explicit argument is required to be passed. The instance samp1 will be passed as argument to the myFunc(). The line samp1.myFunc2() will generate the error :
Traceback (most recent call last): File "/home/4f130d34a1a72402e0d26bab554c2cf6.py", line 26, in samp1.myFunc2() #----------> error line TypeError: myFunc2() takes 0 positional arguments but 1 was given
It means that this method is unbound. It does not accept any instance as an argument. These functions are unbound functions.
Unbound methods and Static methods
Methods that do not have an instance of the class as the first argument are known as unbound methods. As of Python 3.0, the unbound methods have been removed from the language. They are not bounded with any specific object of the class. To make the method myFunc2() work in the above class it should be made into a static method
Static methods are similar to class methods but are bound completely to class instead of particular objects. They are accessed using class names.
Need for making a method static
Not all the methods need to alter the instances of a class. They might serve any common purpose. A method may be a utility function also.
For example, When we need to use certain mathematical functions, we use the built in class
Math. The methods in this class are made static because they have nothing to do with specific objects. They do common actions. Thus each time it is not an optimized way to write as:
So they can be simply accessed using their class name as
A method can be made static in two ways:
- Using staticmethod()
- Using decorator
Using staticmethod(): The
staticmethod() function takes the function to be converted as its argument and returns the static version of that function. A static function knows nothing about the class, it just works with the parameters passed to it.
I am A from the static method
Using decorators: These are features of Python used for modifying one part of the program using another part of the program at the time of compilation. The decorator that can be used to make a method static is
This informs the built-in default metaclass not to create any bound methods for this method. Once this line is added before a function, the function can be called using the class name. Consider the example taken for the Bound method where we encountered an error. To overcome that, it can be written as:
My name is A from object 1 I am not a bound method !!! My name is B from object 2 My name is C from object 2 My name is A from object 1
Here, the line sample.myFunc2() runs without any error and the print() within it works perfectly and gives the output I am not a bound method!!!
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