Value Object

Info:	DDD Value Object implementation.
Author:	Paweł Zadrożny @pawelzny <pawel.zny@gmail.com>

Features

• Value Objects are immutable.
• Two objects with the same values are considered equal
• Access to values with dot notation: value.my_attr
• Access to values by key: value['my_attr']

Installation

pipenv install vo  # or pip install vo

Package: https://pypi.org/project/vo/

Documentation

• Full documentation: http://vo.readthedocs.io
• Public API: http://vo.readthedocs.io/en/latest/api.html
• Examples and usage ideas: http://vo.readthedocs.io/en/latest/examples.html

Quick Example

Value accept any key=value pairs. These pairs will be attached to object as attributes. Once created values are immutable. Attributes can't be changed or deleted.

>>> from vo import Value
>>> book = Value(title='Learning Python',
...              authors=['Mark Lutz', 'David Ascher'],
...              publisher="O'REILLY")
>>> book
Value(authors=['Mark Lutz', 'David Ascher'], publisher="O'REILLY", title='Learning Python')

>>> str(book)
'{"authors": ["Mark Lutz", "David Ascher"], "publisher": "O\'REILLY", "title": "Learning Python"}'

Warning

Any attempt of value modification or delete will raise ImmutableInstanceError

>>> from vo import Value
>>> book = Value(title='Learning Python',
...              authors=['Mark Lutz', 'David Ascher'],
...              publisher="O'REILLY")
>>> book.title = 'Spam'
Traceback (most recent call last):
  File "<input>", line 1, in <module>
    raise ImmutableInstanceError()
  vo.value.ImmutableInstanceError: Modification of Value frozen instance is forbidden.

Values access

Values can be accessed like object attributes or like dict keys.

>>> from vo import Value
>>> book = Value(title='Learning Python',
...              authors=['Mark Lutz', 'David Ascher'],
...              publisher="O'REILLY")
>>> book.title == book['title']
True

>>> book.authors == book['authors']
True

Objects comparison

Let's take the same book example.

>>> from vo import Value
>>> book1 = Value(title='Learning Python',
...               authors=['Mark Lutz', 'David Ascher'],
...               publisher="O'REILLY")
>>> book2 = Value(title='Learning Python',
...               authors=['Mark Lutz', 'David Ascher'],
...               publisher="O'REILLY")
>>> book1 == book2
True

>>> book1 is book2
False

Value lookup

Check if value exists.

>>> from vo import Value
>>> book = Value(title='Learning Python',
...              authors=['Mark Lutz', 'David Ascher'],
...              publisher="O'REILLY")
>>> 'title' in book
True

>>> 'price' in book
False

>>> book.title
'Learning Python'

>>> book.price
Traceback (most recent call last):
  File "<input>", line 1, in <module>
AttributeError: 'Value' object has no attribute 'price'