Static variables in python classes

Static Class Variables in Python

Static class variables in Python are variables that are declared on the class level, not on per-instance variables. These static class variables cannot be changed once initialized. It lets you create global constants, which is useful for things like giving values that always exist a universal name. Static class variables are specifically used to store such data. Static class variables can be placed at the top level of a module, or they can be placed inside methods and classes. Static class variables are a way of creating variables within your class that is shared by all instances of that class. They can help make your code more readable and helps your class become easier to create and understand, while also allowing the values to be accessed easily.

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Declaring static variable inside the class

In Python, static variables are variables that are declared inside a class module rather than in a method. Variables defined within this class cannot be directly accessed, but they can be called by the class where they are defined. A static variable is not only known as a static variable but also as a class variable. Objects cannot be modified their state because the variables belong to the class.

#naming Class, don't forget " : ", to give justice to pythonic syntax class site_name: #class attributes or static class variables host_name= 'Entechin' TLD_name = '.com' print("hostname :", site_name.host_name) print("TLDomain name :", site_name.TLD_name)

hostname : Entechin TLDomain name : .com 

Declaring static variable inside the method

The first thing we need to do is create a class called site_name. Creating a method “site” using the ‘def’ keyword. Inside this method printing the static variable. As a result, we can directly use the data attributes of the site() method by using the site_name class module. Lastly, printing the static variable for the object of the class site. Creating three static variables and printing their instance attributes by storing the results in the class object. Then using class object “site” with the instances respectively with the instances attributes.

Objects representing instances of the class are called self-objects. By using the Python keyword “self”, we can access a class’ attributes and methods.

class site_name: character = 0 def __init__(self, name, TLD , niche): self.name = name self.TLD = TLD self .niche = niche site_name.character += 1 site=site_name('Entechin','.com','Education') print(site.name) print(site.TLD) print(site.niche)

assessing a static variable inside a method

In this approach, a class variable or static class variables are declared inside the class and accessed within the defined module. Within the module the static variable can be used or called along with class modules like site_name.host_name, site_name is class and host_name is class variable.

Within the method, using concatenation with the help of using a class module with a class variable, we can print the static variable.

However, to print the information used in a module or to print the static variables, it’s necessary to create an object for a class and store the class variable in the object class variable.

#naming Class, don't forget " : ", to give justice to pythonic syntax class site_name: #class attributes or static class variables host_name= 'Entechin' TLD_name = '.com' #define a method def site(self): #it returns the static variables by using class variables by class module return str('www.') + ' ' + site_name.host_name + site_name.TLD_name #printing a static variable print("host_name :", site_name.host_name) print("TLD_name :", site_name.TLD_name) # creating an object for class "site_name" url = site_name() print("\nurl :", url.site())

host_name : Entechin TLD_name : .com url : www. Entechin.com 

Conclusion

On this page, we learned a different approach to accessing the class or static variable. The purpose of this post is to clarify some of the finer points of static variables in Python classes. It is important to be aware that Python has limitations that should be taken into consideration before implementing a static variable or method. For example, you can only access a static variable from within a class or within the class method.

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What is a Static Variable in Python?

Imagine walking into a bakery and seeing a wide assortment of freshly-baked cakes over there. You see red-velvet, black-forest, chocolate-truffle, butterscotch cakes, and many more varieties of cakes. While there are different types of cakes, they have one common connection linking them: they are all cakes.

So, talking about our bakery example, the class containing the cakes may have a variable ‘cake’ associated with it. This variable is known as a static variable . In Python programming, a static variable is said to be a class variable that is common to all class members. A static variable is declared within that class but outside the methods within the given class.

Non-static variables are those variables that are associated with the objects or methods declared within the class. They are not the same for all the objects in a given class and differ, as opposed to static variables that remain constant for a given class. The flavors and the prices are non-static variables associated with different cake objects and vary accordingly.

If you are unfamiliar with classes in python, check out this insightful article before reading about static variables.

The output for the code mentioned above will be 2 . Within the class * ‘Demo’*, a static variable ‘i‘ is defined.

Example of Static Variables

Let us look at the bakery example here to understand static variables. In this example, the class ‘Bakery’ has the class/static variable ‘type’ associated with it. This static variable holds the value ‘cake’. This means that all the objects created in the class ‘Bakery’ will be cakes. The static variable is responsible for categorizing all the objects in the ‘Bakery’ with the same ‘type’. ‘Flavor’ and ‘price’ are the instance variables which vary per object.

Explanation:

The objects declared in the class include a Butterscotch cake of Rs 300 stored in ‘a’ and a Chocolate-Truffle Cake costing Rs 250 stored in ‘b’.

How to Access Static Variables from inside a Class?

Static variables can be accessed either from within or outside a class. In the example below, we are updating the number of cakes after each iteration.

While accessing the noOfCakes static variable can either be accessed by using the argument ‘cls’ or by simply using the class name.

Explanation:

The static variables could be accessed from inside a class either by using the classname(‘Cake’ or by using ‘cls’)

The value of the cake stored in the static variable is updated after each step.

How to Access Static Variables from Outside a Class?

Static variables can also be accessed from outside a given class. This could be done by either using objects or class names.

Explanation:

In the above code, it could be seen that outside a class, static variables can be accessed in two ways.

In the first two print statements, static variables have been accessed and printed by using the c1 and c2 objects. In the third statement, the static variable has been accessed by using the class name ‘Cake’.

Conclusion

1. Static variables are those variables that are declared within a given class but outside the objects in the class.
2. Class or static variables can be referred through a by class, but not through an instance directly.
3. Python doesn’t require users to use the ‘static’ keyword before declaring static variables.
4. Static variables can be accessed either from outside the class or from within the class.
5. Static variables could be accessed either by using class names or by using objects.

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Class or Static Variables in Python

All objects share class or static variables. An instance or non-static variables are different for different objects (every object has a copy). For example, let a Computer Science Student be represented by a class CSStudent. The class may have a static variable whose value is “cse” for all objects. And class may also have non-static members like name and roll.

In C++ and Java, we can use static keywords to make a variable a class variable. The variables which don’t have a preceding static keyword are instance variables. See this for the Java example and this for the C++ example.

Explanation:

In Python, a static variable is a variable that is shared among all instances of a class, rather than being unique to each instance. It is also sometimes referred to as a class variable, because it belongs to the class itself rather than any particular instance of the class.

Static variables are defined inside the class definition, but outside of any method definitions. They are typically initialized with a value, just like an instance variable, but they can be accessed and modified through the class itself, rather than through an instance.

Features of Static Variables

• Static variables are allocated memory once when the object for the class is created for the first time.
• Static variables are created outside of methods but inside a class
• Static variables can be accessed through a class but not directly with an instance.
• Static variables behavior doesn’t change for every object.

The Python approach is simple; it doesn’t require a static keyword.

Note: All variables which are assigned a value in the class declaration are class variables. And variables that are assigned values inside methods are instance variables.

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Example:

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Explanation:

in this example, we define a class MyClass that has a static variable static_var initialized to 0. We also define an instance variable instance_var that is unique to each instance of the class.

When we create an instance of the class (obj1), we increment the value of the static variable by 1 and assign it to the instance variable. When we create another instance of the class (obj2), we increment the static variable again and assign the new value to the instance variable for that instance.

Finally, we print out the value of the static variable using the class itself, rather than an instance of the class. As you can see, the value of the static variable is shared among all instances of the class, and it is incremented each time a new instance is created.

Static variables can be useful for maintaining state across all instances of a class, or for sharing data among all instances of a class. However, it’s important to use them carefully and to ensure that their values are synchronized with the state of the program, especially in a multithreaded environment.

Advantages:

• Memory efficiency: Since static variables are shared among all instances of a class, they can save memory by avoiding the need to create multiple copies of the same data.
• Shared state: Static variables can provide a way to maintain shared state across all instances of a class, allowing all instances to access and modify the same data.
• Easy to access: Static variables can be accessed using the class name itself, without needing an instance of the class. This can make it more convenient to access and modify the data stored in a static variable.
• Initialization: Static variables can be initialized when the class is defined, making it easy to ensure that the variable has a valid starting value.
• Readability: Static variables can improve the readability of the code, as they clearly indicate that the data stored in the variable is shared among all instances of the class.

Disadvantages:

• Inflexibility: Static variables can be inflexible, as their values are shared across all instances of the class, making it difficult to have different values for different instances.
• Hidden dependencies: Static variables can create hidden dependencies between different parts of the code, making it difficult to understand and modify the code.
• Thread safety: Static variables can be problematic in a multithreaded environment, as they can introduce race conditions and synchronization issues if not properly synchronized.
• Namespace pollution: Static variables can add to the namespace of the class, potentially causing name conflicts and making it harder to maintain the code.
• Testing: Static variables can make it more difficult to write effective unit tests, as the state of the static variable may affect the behavior of the class and its methods.

Overall, static variables can be a useful tool in Python programming, but they should be used with care and attention to potential downsides, such as inflexibility, hidden dependencies, and thread safety concerns.

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