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README.md

Immutable Python class

Immutable is a class designed to create immutable instances. The attributes of any subclass of Immutable will be read-only.

Examples

Create a subclass of Immutable and initialise it:

class Dog(Immutable):
    def __init__(self, name, colour):
        super(TetrisPiece, self).__init__(attrs_dict={
            "name": name,
            "colour": colour
        })

misty = Dog("Misty", "black")

Run tests

• Install Python 3
• python3 -m venv venv
• pip install
• nosetests

immutable.py

"""Classes: Immutable."""


class Immutable(object):
    """Subclasses of Immutable will have immutable attributes."""

    def __init__(self, attrs_dict=None):   # noqa: D107
        if attrs_dict is not None:
            object.__setattr__(self, '_attrs_dict', attrs_dict)
        else:
            object.__setattr__(self, '_attrs_dict', {})

    # Setting is prevented if attribute is already set
    def __setattr__(self, attr, val):
        """Set attribute value if not already set."""
        if attr in object.__getattribute__(self, '_attrs_dict'):
            raise AttributeError(f"Attribute '{attr}' of {self.__class__.__name__} object is not writable'")
        object.__getattribute__(self, '_attrs_dict')[attr] = val

    # None is returned if attr is not set
    def __getattribute__(self, attr):
        """Get attribute value."""
        if attr in object.__getattribute__(self, '_attrs_dict'):
            return object.__getattribute__(self, '_attrs_dict')[attr]

        else:
            try:
                return object.__getattribute__(self, attr)

            except AttributeError:
                return None

    def to_dict(self):
        """Get dictionary representation of this object's attributes."""
        return object.__getattribute__(self, '_attrs_dict')

test_immutable.py

"""Unit tests for Immutable."""

import unittest

from immutable import Immutable


class ImmutableTestCase(unittest.TestCase):  # noqa: D101
    def test_should_get_attr(self):  # noqa: D102
        obj = Immutable()

        obj.test = 'test'

        self.assertEquals('test', obj.test)

    def test_should_get_raise_attribute_error_when_attr_is_set_twice(self):  # noqa: D102
        obj = Immutable()

        obj.test = 'test'

        with self.assertRaises(AttributeError):
            obj.test = 'new'

    def test_should_get_none_when_attr_is_not_set(self):  # noqa: D102
        obj = Immutable()

        self.assertEquals(None, obj.test)

    def test_should_convert_to_dict(self):  # noqa: D102
        obj = Immutable()

        obj.a = 'a'
        obj.b = 'b'

        dict = obj.to_dict()

        self.assertIn('a', dict)
        self.assertIn('b', dict)
        self.assertEquals(obj.a, dict['a'])
        self.assertEquals(obj.b, dict['b'])