This content originally appeared on DEV Community and was authored by dev0928
Data classes is a new feature introduced in Python 3.7. This feature aims to reduce boilerplate code sucs as __init__() and __eq()__ methods in user-defined Python classes. By using the dataclasses module’s decorators and functions, one can create concise Python classes. Let’s review the use of the data classes feature with an example.
Employee class could be declared concisely like shown below with the data classes decorator.
from dataclasses import dataclass, field
@dataclass
class Employee:
id: int
first_name: str
last_name: str
email: str
base_pay: float
tax_rate: float = field(default=0.01, init=False)
hobbies: list = field(default_factory=list())
def calculate_pay(self):
net_pay = self.base_pay - (self.base_pay * self.tax_rate)
return net_pay
emp1 = Employee(1, 'John', 'Doe', 'john.doe@example.com', 10000, ['Fishing', 'Soccer'])
print(emp1) #Employee(id=1, first_name='John', last_name='Doe', email='john.doe@example.com', base_pay=10000, tax_rate=0.01, hobbies=['Fishing', 'Soccer'])
print(emp1.calculate_pay()) #9900.0
-
@dataclassdecorator above generatesinit,reprandeqmethods by default.@dataclassgenerator without any parameters like declared above is equivalent to the below declaration:
@dataclass(init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False)
- If
orderparameter is set to true, it will generate boilerplate methodslt,gt,le, andge. Also, true value supplied to theunsafe_hashparameter would generatehashmethod. - Dataclasses use the
typingmodule to define the data type of the declared class fields. However, if one wishes to not specify the field data types, they can usetyping.Anyfor all of their fields in the class. - By default, all fields of the class are included in the generated methods. But this can be customizable using field declaration. For example,
tax_ratefield in the example is excluded from theinitmethod.
tax_rate: float = field(default=0.01, init=False)
- Also, we can use the
default_factoryparameter to initialize complex data types such as list. - Dataclasses module has several convenience functions. For example,
dataclasses.fieldsfunction provides a list of fields in the form of tuple. Also,dataclasses.asdictreturns a dictionary representation of the supplied object.
Dataclasses is one of the powerful features introduced in the recent versions of Python. Here is the link for learning more about it's capabilities so you can start using this feature in your projects.
This content originally appeared on DEV Community and was authored by dev0928
dev0928 | Sciencx (2021-04-12T00:59:33+00:00) What are Data Classes in Python?. Retrieved from https://www.scien.cx/2021/04/12/what-are-data-classes-in-python/
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