README.v2.rst

simple_model

As the name suggests, this is a very simple model framework. It can be used for data validation and (de-)serialization.

Installation

Install with pip:

$ pip install --user simple_model

Usage

This allows me to test the examples by taking care of sorting the dictionaries, it is not required for simple_model to work:

>>> from pprint import pprint

Note: casting Data to a dict as it is done here is unnecessary as well. However pprint does not sort models in Python 2 without the cast for some reason.

Examples:

>>> from simple_model.v2 import Model, Attribute, ModelError

>>> @Model(drop_unknown=True)
... @Attribute('name', type=str)
... @Attribute('some_value', type=str, optional=True, nullable=True)
... @Attribute('another_value', type=int, default=0)
... class Data(object):
...     pass

>>> pprint(dict(Data(name = 'test', some_value = None, another_value = 12)))
{'another_value': 12, 'name': 'test', 'some_value': None}

>>> pprint(dict(Data(name = 'test')))
{'another_value': 0, 'name': 'test', 'some_value': Ellipsis}

>>> init_dict = {'name': 'test', 'some_value': 'val', 'another_value': 3}
>>> pprint(dict(Data(**init_dict)))
{'another_value': 3, 'name': 'test', 'some_value': 'val'}

Initializing with missing attributes while not specifying them as optional or providing a fallback value will result in a ValueError containing all failed attributes. Note that fallback takes precedence over optional, specifying both is unnecessary.

Unknown values will be ignored for Models with drop_unknown set to True

>>> pprint(dict(Data(name = 'test', unknown_value = True)))
{'another_value': 0, 'name': 'test', 'some_value': Ellipsis}

Serialization can be achieved easily, for example

>>> import json
>>> def serialize(model):
...     return json.dumps(model)

>>> def deserialize(string):
...     return Data(**json.loads(string))

Since the Model class simply calls the Attribute class for each parameter and the Attribute class in turn calls the given 'type', one could easily use functions instead of types to achieve more complex results and value parsing

>>> from datetime import datetime
>>> def parse_date(string):
...     return datetime.strptime(string, '%Y-%m-%d')

>>> @Model()
... @Attribute('date', type=parse_date)
... class Data(object):
...     pass

>>> Data(date='2015-11-20')
{'date': datetime.datetime(2015, 11, 20, 0, 0)}

Fallback values can also be given as functions

>>> def fun():
...     return "foo"

>>> @Model()
... @Attribute('point', type=str, fdefault=fun)
... class Data(object):
...     pass

>>> Data()
{'point': 'foo'}

If you need to verify Lists of objects, use functions

>>> @Model()
... @Attribute('points', type=lambda l: list(map(str, l)))
... class Data(object):
...     pass

>>> Data(points=['abc', 'def', 'ghi'])
{'points': ['abc', 'def', 'ghi']}

Or the included list_type helper class

>>> from simple_model.helpers import list_type

>>> @Model()
... @Attribute('points', type=list_type(str))
... class Data(object):
...     pass

>>> Data(points=['abc', 'def', 'ghi'])
{'points': ['abc', 'def', 'ghi']}

For more complex data, use Models to verify

>>> @Model()
... @Attribute('some_value', type=str)
... @Attribute('some_other_value', type=int)
... class SubData(object):
...     pass

>>> @Model()
... @Attribute('point', type=SubData)
... class Data(object):
...     pass

>>> pprint(dict(Data(point={'some_value': 'abc', 'some_other_value': 12})))
{'point': {'some_other_value': 12, 'some_value': 'abc'}}

>>> sub_data = SubData(some_value='abc', some_other_value=12)
>>> pprint(dict(Data(point=sub_data)))
{'point': {'some_other_value': 12, 'some_value': 'abc'}}

To allow uncommon names, use the Attribute name keyword

>>> @Model()
... @Attribute('point', type=str, alias='@point')
... class Data(object):
...     pass

>>> Data(point='something')
{'@point': 'something'}

>>> Data(**{ '@point': 'something' })
{'@point': 'something'}

To easily check against expected values you can use the helper function one_of

>>> from simple_model.helpers import one_of

>>> @Model()
... @Attribute('foo', type=one_of('bar', 'foobar'))
... class Data(object):
...     pass

>>> Data(foo='bar')
{'foo': 'bar'}

>>> Data(foo='foo') # doctest: +ELLIPSIS +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
    ...
simple_model.v2.ModelError: Data
- attribute: foo
  value: "foo"
  exception: must be one of ('bar', 'foobar') but was 'foo'

If you want to disallow unknown values, set the ignore_unknown attribute to False

>>> @Model(ignore_unknown=False)
... @Attribute('point', type=str)
... class Data(object):
...     pass

>>> Data(point = 'abc', other = 'def') # doctest: +ELLIPSIS +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
    ...
simple_model.v2.ModelError: Data
- attribute: None
  value: "def"
  exception: Unknown attribute "other"

Models are mutable by default

>>> @Model()
... @Attribute('point', type=int)
... class Data(object):
...     pass

>>> d = Data(point = 1)
>>> d.point
1
>>> d.point = 2
>>> d.point
2

You can set Models to be immutable

>>> @Model(mutable=False)
... @Attribute('point', type=int)
... class Data(object):
...     pass

>>> d = Data(point = 1)
>>> d.point
1
>>> d.point = 2
Traceback (most recent call last):
    ...
AttributeError: can't set attribute

This can also be done on a per Attribute basis

>>> @Model()
... @Attribute('point', type=int, mutable=True)
... class Data(object):
...     pass

>>> d = Data(point=12)
>>> d.point
12
>>> d.point = 2
>>> d.point
2

Attributes can take a transformation function to execute when setting the value

>>> import hashlib

>>> @Model()
... @Attribute('username', type=str)
... @Attribute('password', type=str, transformation=lambda s: hashlib.md5(s.encode()).hexdigest())
... class User(object):
...     pass

>>> u = User(username='foobar', password='foobaz')
>>> u.password
'80338e79d2ca9b9c090ebaaa2ef293c7'

Note: This only works with new-style python classes, so make sure to inherit object if you're using python 2.

Tests

To run the tests use tox:

$ tox

Issues

Please submit any issues on GitHub.

Changelog

see CHANGELOG