A “Data class” is a coding pattern featuring a collection of fields with little or no extra functionality.

This chapter covers three data class builders: collections.namedtuple, typing.NamedTuple and @dataclasses.dataclass

Overview of Data Class Builders #

Consider the following Coordinate class:

class Coordinate:
    def __init__(self, lat, lon):
        self.lat = lat
        self.lon = lon

Notice that if we were to add another attribute, we will need to mention it three times.

Also string representation and comparison between objects do not work the way we expect:

>>> moscow = Coordinate(55.76, 37.62)
>>> moscow
<__main__.Coordinate object at 0x104868590>
>>> location = Coordinate(55.76, 37.62)
>>> location == moscow
False
>>> (location.lat, location.lon) == (moscow.lat, moscow.lon)
True

Next we consider the same Coordinate class but built with collections.namedtuple:

from collections import namedtuple
Coordinate = namedtuple('Coordinate', 'lat lon')
>>> moscow = Coordinate(55.76, 37.62)
>>> moscow
Coordinate(lat=55.76, lon=37.62)
>>> moscow == Coordinate(lat=55.76, lon=37.62)
True

__repr__ and __eq__ are meaningful here.

See page 165 for an example using typing.NamedTuple.