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What are important features of dataclasses in Python?

Answer»

The dataclasses module is one of the most recent modules to be added in Python's standard library. It has been INTRODUCED since version 3.7 and defines @dataclass decorator that automatically generates following methods in a user defined class:

constructor METHOD __init__() STRING representation method __repr__() __eq__() method which overloads == operator

The dataclass function decorator has following prototype:

@dataclass(init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False)

All the arguments are of Boolean value. Each decides whether a corresponding magic method will be automatically generated or not.

The 'init' parameter is True by default which will automatically generate __init__() method for the class.

Let us define Employee class using dataclass decorator as follows:

#data_class.py from dataclasses import dataclass @dataclass class Employee(object):      NAME : str      age : int      salary : float

The auto-generated __init__() method is like:

def __init__(self, name: str, age: int, salary: float):        self.name = name        self.age = age        self.salary = salary

Auto-generation will not happen if the class contsins explicit definition of __init__() method.

The repr argument is ALSO true by default.  A __repr__() method will be generated. Again the repr string will not be auto-generated if class provides explicit definition.

The eq argument forces __eq__() method to be generated. This method gets called in response to equals comparison operator (==). Similarly other operator overloading magic methods will be generated if the order argument is true (the default is False), __lt__(), __le__(), __gt__(), and __ge__() methods will be generated, they implement comparison operators < <= > ans >= respectively.

If unsafe_hash argument is set to False (the default), a __hash__() method is generated according to how eq and frozen are set.

frozen argument: If true (the default is False), it emulates read-only frozen instances.

>>> from data_class import Employee >>> e1=Employee('XYZ', 21, 2150.50) >>> e2=Employee('xyz', 20, 5000.00) >>> e1==e2 False

Other useful functions in this module are as follows:

asdict():

This function converts class instance into a dictionary object.

>>> import dataclasses >>> dataclasses.asdict(e1) {'name': 'XYZ', 'age': 21, 'salary': 2150.5}

astuple():

This function converts class instance into a tuple object.

>>> dataclasses.astuple(e2) ('xyz', 20, 5000.0)

make_dataclass():

This function creates a new dataclass from the list of tuples given as fields argument.

>>> NewClass=dataclasses.make_dataclass('NewClass', [('x',int),('y',float)]) >>> n=NewClass(10,20) >>> n NewClass(x=10, y=20)


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