Skip to main content
Donate to the Python Software Foundation or Purchase a PyCharm License to Benefit the PSF! Donate Now

A simple mixin for create Value Objects

Project description

Version Number Build Status Coverage Status Requirements Status Python Version License GPLv3

Based on Ruby Gem by NoFlopSquad (https://github.com/noflopsquad/value-object)

A value object is a small object that represents a simple entity whose equality isn’t based on identity: i.e. two value objects are equal when they have the same value, not necessarily being the same object.

Wikipedia.

Installation

> pip install simple-value-object

Usage

Constructor and field readers

from simple_value_object import ValueObject

class Point(ValueObject):
    def __init__(self, x, y):
        pass

point = Point(1, 2)

point.x
# 1

point.y
# 2

point.x = 5
# CannotBeChangeException: You cannot change values from a Value Object, create a new one

class Date(ValueObject):
    def __init__(self, day, month, year):
        pass

date = Date(1, 10, 2015)

date.day
# 1

date.month
# 10

date.year
# 2015

date.month = 5
# CannotBeChangeException: You cannot change values from a Value Object, create a new one

Equality based on field values

from simple_value_object import ValueObject

class Point(ValueObject):
    def __init__(self, x, y):
        pass

a_point = Point(5, 3)

same_point = Point(5, 3)

a_point == same_point
# True

a_different_point = Point(6, 3)

a_point == a_different_point
# False

Hash code based on field values

from simple_value_object import ValueObject

class Point(ValueObject):
    def __init__(self, x, y):
        pass

a_point = Point(5, 3)

same_point = Point(5, 3)

a_point.hash == same_point.hash
# True

a_different_point = Point.new(6, 3)

a_point.hash == a_different_point.hash
# False

Invariants

from simple_value_object import ValueObject, invariant

class Point(ValueObject):

    def __init__(self, x, y):
        pass

    @invariant
    def inside_first_quadrant(cls, instance):
        return instance.x > 0 and instance.y > 0

    @invariant
    def x_less_than_y(cls, instance):
        return instance.x < instance.y

Point(-5, 3)
#ViolatedInvariantException: Args values [-5, 3] violates invariant: inside_first_cuadrant

Point(6, 3)
#ViolatedInvariantException: Args values [6, 3] violates invariant: x_less_than_y

Point(1,3)
#<__main__.Point at 0x7f2bd043c780>

Mutable types not allowed

from simple_value_object import ValueObject, invariant

class AValueObject(ValueObject):

    def __init__(self, an_arg):
        pass

AValueObject(an_arg={'key': 'value'})
#MutableTypeNotAllowedException: 'an_arg' cannot be a mutable data type.

AValueObject({'key': 'value'})
#MutableTypeNotAllowedException: Mutable args are not allowed.

ValueObject within ValueObject

from simple_value_object import ValueObject, invariant

class Money(ValueObject):
    def __init__(self, amount, currency):
        pass

class Currency(ValueObject):
    def __init__(self, symbol):
        pass

Money(amount=100, currency=Currency(symbol="€"))

Test

> pip install -r requirements-test.txt
> PYTHONPATH=$PYTHONPATH:. mamba

Project details


Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Filename, size & hash SHA256 hash help File type Python version Upload date
simple_value_object-1.3-py2-none-any.whl (5.1 kB) Copy SHA256 hash SHA256 Wheel 2.7
simple-value-object-1.3.tar.gz (4.4 kB) Copy SHA256 hash SHA256 Source None

Supported by

Elastic Elastic Search Pingdom Pingdom Monitoring Google Google BigQuery Sentry Sentry Error logging AWS AWS Cloud computing DataDog DataDog Monitoring Fastly Fastly CDN SignalFx SignalFx Supporter DigiCert DigiCert EV certificate StatusPage StatusPage Status page