Python’s dataclasses and keyword-only fields

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Now, if you’ve been living under a rock for the past few years or just don’t care much about data classes (which is understandable), let me give you a quick rundown of what they are and why you should care.

Data classes are essentially a way to create lightweight objects with minimal boilerplate code. They allow us to define our own custom object types without having to inherit from an existing class or implement all the necessary methods ourselves. This can save us time, effort, and headaches in the long run.

But what if we want to make things even easier for ourselves? What if we don’t want to have to specify every single field when creating a new object instance? That’s where keyword-only fields come in! With this feature, we can mark certain fields as “keyword-only”, which means that they must be specified using their names instead of positional arguments.

Here’s an example:

# Importing the necessary module
from dataclasses import dataclass, field

# Creating a dataclass with keyword-only fields
@dataclass(kw_only=True)
class Birthday:
    # Defining the fields with their respective data types
    name: str
    birthday: datetime.date

# Creating a new object instance using keyword-only fields
birthday = Birthday(name="John Doe", birthday=datetime.date(2000, 1, 1))

# The "kw_only" parameter ensures that the fields can only be specified using their names instead of positional arguments
# This allows for more flexibility and avoids having to specify every single field when creating a new object instance.

As you can see, we’ve marked the “Birthday” class as having all its fields be keyword-only using the `kw_only=True` argument in our dataclass decorator. This means that when creating a new object instance, we must specify each field by name instead of positional arguments.

But what if we only want to mark certain fields as keyword-only? No problem! We can do that too:

# Importing the necessary module for creating dataclasses
from dataclasses import dataclass, field

# Creating a dataclass called "Birthday" with two fields: "name" and "birthday"
@dataclass
class Birthday:
    name: str
    birthday: datetime.date = field(kw_only=True) # Setting the "birthday" field as keyword-only using the "kw_only=True" argument in the dataclass decorator

# Creating a new object instance of the "Birthday" class, specifying the "birthday" field using keyword argument
birthday2 = Birthday("John Doe", birthday=datetime.date(2000, 1, 1)) # Using the datetime.date function to specify the date for the "birthday" field

In this example, we’ve marked the “birthday” field as being keyword-only using the `kw_only=True` argument in our dataclass decorator for that specific field. This means that when creating a new object instance, we must specify the “name” field by positional arguments and the “birthday” field by name instead of positional arguments.

Dataclasses with keyword-only fields a powerful combination that can save us time and effort in our Python code.

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