Immutable object: Difference between revisions

Revision as of 04:44, 27 July 2020

Revision as of 18:30, 27 July 2020

Line 305:

__delattr__ = __setattr__

def __init__(self, x, y) -> None:

# We can no longer use self.value = value to store the instance data

# so we must explicitly call the superclass

Line 312:

</syntaxhighlight>

The standard library helperhelpers [https://docs.python.org/3.3/library/collections.html#collections.namedtuple collections.namedtuple] createsand [https://docs.python.org/3/library/typing.html#typing.NamedTuple typing.NamedTuple], available from Python 3.6 onward, create simple immutable classes. The following example is roughly equivalent to the above, plus some tuple-like features:

<syntaxhighlight lang="python">

from typing import NamedTuple

import collections

Point = collections.namedtuple('Point', ['x', 'y'])

# the following creates a similar namedtuple to the above

class Point(NamedTuple):

x: int

y: int

</syntaxhighlight>

Introduced in Python 3.7, [https://docs.python.org/3/library/dataclasses.html dataclasses] allow developers to emulate immutability with [https://docs.python.org/3/library/dataclasses.html#frozen-instances frozen instances]. If a frozen dataclass is built, dataclasses will override __setattr__() and __delattr__() to raise FrozenInstanceError if invoked.

is roughly equivalent to the above, plus some tuple-like features.

<syntaxhighlight lang="python">

from dataclasses import dataclass

@dataclass(frozen=True)

class Point:

x: int

y: int

</syntaxhighlight>

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