Short notes on namedtuples, NamedTuples and Data classes

Mon, 11 Jan 2021 21:28:43 -0500

Both dataclasses and tuples are based on the attrs project, the one Python Library everybody needs and are fast object types (factory methods) designed to simplify and reduce code.

namedtuple and NamedTuple

Both immutable
Tuple-based (hence fast) but far better than tuples
NamedTuple is the typed version of namedtuple
immutable, iterable, hashable, unpackable
backward-compatible with tuple (e.g you can access a namedtuple by index)
default arguments supported from Python 3.7+
fast! C-based
example ¹

Point = namedtuple('Point', 'x y')
pt1 = Point(1.0, 5.0)
pt2 = Point(2.5, 1.5)

from math import sqrt
# use index referencing
line_length = sqrt((pt1[0]-pt2[0])**2 + (pt1[1]-pt2[1])**2)
 # use tuple unpacking
x1, y1 = pt1

Dataclasses

Are mutable
post-init processing can be used to create fields depending on other fields or even to perform input validation²
all implementation is written in Python, so slower wrt tuple-based data types
Validation of types at runtime not supported natively (or cumbersome) but easy with decorator @enforce_typing
from Python 3.7
are just regular Classes (e.g. inheritance) withot writing boilerplate code
inappropriate when API compatibility with tuples or dicts is requested
bonus PyCon talk, if you have time
example³

from dataclasses import dataclass

@dataclass(unsafe_hash=True)
class InventoryItem:
 '''Class for keeping track of an item in inventory.'''
 name: str
 unit_price: float
 quantity_on_hand: int = 0

 def total_cost(self) -> float:
 return self.unit_price * self.quantity_on_hand

Other fancy data types (not from the stdlib)

pydantic: enforces type hints at runtime providing user-readable errors when data is invalid. Seems relatively popular.

# sample input val via Regexp
from dataclasses import dataclass
import re
@dataclass
class Widget:
 id: int
 def __post_init__(self):
 id_condition = re.match(r"[0-9]{4}", str(self.id))
 if not id_condition:
 print(f"{self.id} doesn't follow pattern [0-9]{{4}}")
 raise CustomException

brief explanation on stackoverlow ↩︎

Data-Structures on AW — notes & thoughts

Short notes on namedtuples, NamedTuples and Data classes

namedtuple and NamedTuple

Dataclasses

Other fancy data types (not from the stdlib)