Understanding Python Dataclass Frozen Attribute: Immutable Objects

Python DataClass: Overview and Benefits

Python DataClass: Overview and Benefits

If you are a Python developer, then you must be familiar with the term data classes in Python. Introduced in Python 3.7 and later updated in Python 3.8, data classes have become one of the most popular and widely used features among Python developers. Python dataclasses are nothing but a way to create classes that are primarily used for storing data and not for implementing complex business logic or performing complex operations. Data classes offer several benefits over traditional Python classes, including ease of use, improved code readability, and reduced boilerplate code.

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Data classes are essentially a lightweight alternative to defining classes using the traditional Python class statement. They allow Python developers to create classes that can be used for storing data with minimal boilerplate code. When using data classes, we don’t have to write the code for a constructor, __repr__ method, or __eq__ method. Instead, Python takes care of generating these methods for us during runtime, based on the fields defined in the class.

Data classes are defined using the @dataclass decorator, which can be found in the dataclasses module that was introduced in Python 3.7. Here is a simple example of how to define a data class:


from dataclasses import dataclass

class Person:
name: str
age: int
email: str

As you can see, defining a data class is straightforward and requires very little code. In the above example, we have defined a data class called Person that has three fields – name, age, and email. We don’t have to write any boilerplate code, such as defining the __init__ method or the __repr__ method. Instead, Python will automatically generate these methods for us when we create an instance of the Person class.

One of the main benefits of using data classes is that they allow us to write code that is more concise and easier to read. With data classes, we can define the fields of a class using type hints, making it easier to understand the structure of the class at a glance. Data classes also make it easier to perform operations on the data stored in the class, such as sorting, filtering, or searching through a list of instances of the same class.

Another significant advantage of using data classes is that they are immutable by default. This means that once an instance of a data class is created, its fields cannot be modified. If we try to modify a field, Python will raise an exception. This can be very useful when working with large codebases or when sharing code with other developers who may not be familiar with the structure of the class. When all the fields in a class are immutable, we can be sure that the values stored in the class will not change unexpectedly, leading to bugs or other errors.

Overall, Python data classes provide a simple, concise, and efficient way to define classes that are primarily used for storing data. With data classes, we can reduce the amount of boilerplate code we need to write, improve the readability of our code, and make it easier to work with instances of the same class. If you are a Python developer, data classes are definitely worth checking out!

Understanding Frozen: What it is and When to Use it

Frozen Python

Python is an object-oriented programming (OOP) language that allows the use of classes. It introduced a new feature called “dataclass” in version 3.7 that is a simple way to create classes with data. It eliminates the need to write a lot of boilerplate code by allowing you to specify the attributes in the class definition. Also, the creation of a constructor and other special methods is automated. One of the features of dataclass is the ability to create immutable objects, and this is where frozen comes into play. In this article, we will discuss the frozen feature of dataclass, what it is, and when to use it.

What is “Frozen”?

Python Frozen

Frozen is a special attribute of dataclass that makes an object immutable. This means that once an object is created, its attribute values cannot be changed. If you try to change the value, a TypeError will be raised. This is similar to tuples in Python. Once you create a tuple, its elements cannot be changed, added, or removed. Having immutable objects can help in many ways. For example, they can be used as keys in dictionaries, and as elements in sets.

Here is an example of how to create a frozen dataclass:

class Employee:
name: str
age: int
salary: float

In the above example, we have created a dataclass called Employee with three attributes: name, age, and salary. The frozen argument is set to True, which makes the objects immutable. Now, let’s create an instance of this class.

emp1 = Employee(‘John’, 30, 5000.0)

As you can see, we have created an object of the Employee class and assigned it to emp1. Let’s try to modify one of its attributes and see what happens.

emp1.salary = 6000.0

If you try the above line of code, Python will raise a TypeError stating that ‘Employee’ object does not support item assignment. This is because the object is immutable due to frozen being set to True.

Now let’s try to change one attribute value. Notice how Python raises an error.

emp1.salary = 6000.0
Traceback (most recent call last):
File ““, line 1, in
dataclasses.FrozenInstanceError: cannot assign to field ‘salary’

When to Use “Frozen”?

Frozen Dataclass

Now that we have a basic understanding of frozen, let’s discuss when to use it. There are specific use cases where we want to create immutable objects. One of the most common scenarios where we use them is when we want to avoid accidental changes to our code’s important values. For example, think of a financial application where a user’s balance is stored in an object. By making that object immutable, we ensure that the balance cannot be modified accidentally by our code. Another use case is in multi-threaded programming, where immutable objects are thread-safe due to their non-changing characteristics. We can use them in programs that require high concurrency, such as web servers, where data should not be shared across threads.

In short, for any case where you want to avoid any non-intentional modifications to your objects and values, frozen is the way to go. They help you write bug-free, reliable, and high-quality code that can be used easily and efficiently in multi-threaded environments.

In conclusion, dataclass has become a very useful feature in Python 3.7 onwards. It has allowed developers to write concise and clean code while reducing the effort of writing class definitions. The frozen attribute is a great addition that has made dataclass even more robust. By making an object immutable, dataclass ensures that its attributes cannot be modified accidentally, offering thread safety and reliability in multi-threaded programming environments.

Implementing Frozen DataClasses in Python

dataclass frozen python

In Python 3.7 and above, a new module called data classes was introduced. Data classes are like regular classes, but they come with a few extra features that make them ideal for creating classes that are used to store data. One of those features is the ability to create a frozen data class. In this article, we will explore how to implement frozen data classes in python.

First, let’s understand what a frozen data class is. A frozen data class is a data class that is immutable, meaning once an instance of the class is created, it cannot be changed. This is useful when we want to create objects that are meant to be read-only and cannot be accidentally modified. Frozen data classes can be defined using the `@dataclass(frozen=True)` decorator.

Let’s look at an example:

from dataclasses import dataclass

class Person:
name: str
age: int

In this example, we have defined a frozen data class called `Person`. The `name` and `age` fields are defined as `str` and `int` types, respectively. Notice that we have used the `@dataclass(frozen=True)` decorator to mark this class as frozen.

Now, let’s try to modify an instance of this class:

person = Person(name=’John Doe’, age=30)
person.age = 31

If we run this code, we will get an error:

Traceback (most recent call last):
File “main.py”, line 4, in
person.age = 31
AttributeError: can’t set attribute

This error occurs because we are trying to modify the `age` field of the `person` instance, which is not allowed because the `Person` class is frozen.

Frozen data classes are particularly useful in scenarios where we want to avoid accidental modifications to our classes. For example, if we are dealing with financial data, we may want to create an immutable class to prevent changes to the data. In such cases, frozen data classes can be a useful tool for maintaining data integrity.

However, it’s important to note that frozen data classes do have a few limitations. For example, frozen data classes cannot be subclassed, and their instances cannot have default values. Additionally, frozen data classes cannot have custom `__init__` methods or any methods that modify the instance’s state. These limitations exist because frozen data classes are designed to be immutable, and any modifications to the class can potentially affect its immutability.

In conclusion, frozen data classes are a useful feature for creating immutable classes in Python. By marking a data class as frozen, we can prevent accidental modifications to our instances and ensure data integrity. However, it’s important to consider the limitations of frozen data classes before using them in our projects.

Frozen vs. Non-Frozen DataClasses: Pros and Cons

Python dataclass frozen

Python 3.7 introduced the dataclass module to simplify the process of creating classes that mainly have data storage and retrieval functionality. This module offers several features to automate the creation of classes in Python. One of these features is the frozen attribute. Data classes with the frozen attribute are marked as immutable, meaning their instances cannot be altered after they are created. In contrast, data classes without the frozen attribute are mutable, meaning their instances are subject to change even after creation. Each option has its pros and cons, and this article explores them in detail.

Pros of Frozen DataClasses


Frozen DataClasses have one primary advantage over non-frozen ones: immutability. You can’t modify the contents of the instances once they are created. This feature comes in handy when you don’t want to change the values in your data storage. For example, if you’re dealing with financial transactions, you wouldn’t want to change the values randomly. Immutable objects have other advantages:

  • They are thread-safe. Because the instances never change, you can use them safely from multiple threads without worrying about race conditions.
  • Better hashing. Immutable objects have fixed hash values that depend on their content. This feature is useful when you need to reference an object without the risk of it changing in the future.
  • Faster comparisons. Comparison of instances takes significantly less time since it is unnecessary to inspect the objects for changes.

Cons of Frozen DataClasses

Difficulty of changing immutable data

Immutable objects have a significant disadvantage: you can’t change them at will. Once you create an instance of a frozen DataClass, it becomes impossible to modify. The only way to change the contents of a frozen instance is to create a new instance with updated values, which can be inefficient. Other downsides include:

  • Less flexibility because the data is unchangeable.
  • Limited use in certain situations as some operations require changeable instances.
  • Extra coding to implement any changes to existing instances.

Pros of Non-Frozen DataClasses


The primary advantage of Non-Frozen DataClasses is their mutability. You can create instances and modify them at will. As a result, this option offers the following benefits:

  • Flexibility because the data is changeable.
  • Can be used in multiple situations including where operations on changeable instances are required.

Cons of Non-Frozen DataClasses

Race conditions

On the downside, Non-Frozen DataClasses can have one significant disadvantage: the possibility of race conditions. Race condition is a bug that occurs when two threads attempt to modify the same object at the same time. This issue can lead to incorrect results and other unwanted behavior. Other downsides of mutable objects include:

  • Performance problems as the contents of instances could change constantly due to the requirement of deep copying of the objects regularly.
  • Difficulty in debugging as it is difficult to keep track of which parts of the code modify the instance.
  • Less secure as sensitive information could be changed and manipulated.

Conclusively, whether to use frozen or non-frozen DataClasses depends on your specific use case. Immutable DataClasses are suitable for situations where you don’t want the contents of an instance to change after it is created and when thread-safety is required. On the other hand, mutable DataClasses are suitable for use in situations that require changeable attributes on the instance themselves. By understanding the pros and cons of each option, you can choose the best one for your specific use case.

Best Practices for Working with Frozen DataClasses in Python

Frozen DataClass

Python’s dataclass module is a great tool for creating structured, immutable data types with minimal boilerplate code. The frozen attribute further enhances the capabilities of dataclasses by making them immutable, preventing changes to their attributes after instantiation.

Here are five best practices for working with frozen dataclasses:

1. Define Frozen DataClasses for Read-Only Objects


When you create a frozen dataclass, you are telling Python that this object should not be modified after it is instantiated. This makes them ideal for read-only objects, such as configuration settings, static data, or database records.

By using frozen dataclasses for read-only objects, you can ensure that they are not accidentally modified later, which can lead to bugs and incorrect behavior.

2. Use Proper Type Annotations

Python Typing

Just like regular dataclasses, frozen dataclasses benefit from proper type annotations. Type annotations allow Python to check the types of variables at runtime, reducing the likelihood of bugs and errors in your code.

By using the typing module in Python, you can define the types of your dataclass attributes, which will make them more readable and easier to work with later on.

3. Avoid Inheritance with Frozen DataClasses

No Inheritance

When defining a frozen dataclass, you cannot inherit from another class. Frozen dataclasses are designed to be simple, minimalistic objects, and inheritance can complicate things. If you try to inherit from a frozen dataclass, you will get a TypeError.

To work around this, it is best to keep frozen dataclasses as stand-alone objects and avoid inheritance whenever possible.

4. Be Careful with Equality and Hashing

Equality and Hashing

When you create a frozen dataclass, Python automatically generates an __eq__ method for comparing instances of the class. It also generates a __hash__ method for using instances as dictionary keys or set elements.

However, if your frozen dataclass contains other objects that also have __eq__ or __hash__ methods, you need to be careful to ensure that equality and hashing work as expected. Because frozen dataclasses are immutable, their hash values should remain consistent over time to avoid issues in dictionary keys or set elements.

5. Use Dataclasses with Other Python Libraries

Popular Python Libraries

Dataclasses are a popular addition to the Python ecosystem and are supported by many Python libraries, such as Flask, Django, and SQLAlchemy. By using dataclasses in your code, you can ensure that your code is compatible with these libraries and can benefit from their features and enhancements.

Dataclasses are also widely used in Python’s scientific computing ecosystem, where they are used for defining and manipulating large, complex datasets.

Overall, frozen dataclasses are a powerful tool for creating immutable, read-only objects in Python. By following these best practices, you can ensure that your frozen dataclasses are easy to work with, compatible with other Python libraries, and free from bugs and errors.

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