tri.declarative 0.17.0

tri.declarative contains class decorators to define classes with subclass semantics in the style of django Model classes.

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tri.declarative
===============

tri.declarative contains class decorators to define classes with subclass semantics in the style of django Model classes.


Running tests
-------------

You need tox installed then just `make test`.


License
-------

BSD


Documentation
-------------

http://declarative.readthedocs.org.


Usage
=====


@declarative
------------

In example below, the :code:`@declarative(str)` decorator will ensure that all :code:`str` members of class Foo will be
collected and sent as :code:`members` constructor keyword argument.

.. code:: python

from tri.declarative import declarative

@declarative(str)
class Foo(object):
bar = 'barbar'
baz = 'bazbaz'
boink = 17

def __init__(self, members):
assert members['bar'] == 'barbar'
assert members['baz'] == 'bazbaz'
assert 'boink' not in members

f = Foo()

The value of the :code:`members` argument will also be collected from sub-classes:

.. code:: python

from tri.declarative import declarative

@declarative(str)
class Foo(object):

def __init__(self, members):
assert members['bar'] == 'barbar'
assert members['baz'] == 'bazbaz'

class MyFoo(Foo):
bar = 'barbar'
baz = 'bazbaz'

def __init__(self):
super(MyFoo, self).__init__()

f = MyFoo()


The :code:`members` argument can be given another name (:code:`things` in the example below).

.. code:: python

from tri.declarative.declarative import declarative

@declarative(str, 'things')
class Foo(object):

bar = 'barbar'

def __init__(self, **kwargs):
assert 'things' in kwargs
assert kwargs['things']['bar'] == 'barbar'

f = Foo()


Note that the collected dict is an :code:`OrderedDict` and will be ordered by class inheritance and by using
:code:`sorted` of the values within each class. (In the 'str' example, :code:`sorted` yields in alphabetical order).

Also note that the collection of *class* members based on their class does *not* interfere with *instance* constructor
argument of the same type.

.. code:: python

from tri.declarative import declarative

@declarative(str)
class Foo(object):
charlie = '3'
alice = '1'

def __init__(self, members):
assert members == OrderedDict([('alice', '1'), ('charlie', '3'),
('bob, '2'), ('dave', '4'),
('eric', '5')])
assert 'animal' not in members


class MyFoo(Foo):
dave = '4'
bob = '2'

class MyOtherFoo(MyFoo):
eric = '5'

def __init__(self, animal)
assert animal == 'elephant'

f = MyOtherFoo('elephant')


@creation_ordered
-----------------

Class decorator that ensures that instances will be ordered after creation order when sorted.

This is useful for classes intended to be used as members of a :code:`@declarative` class when member order matters.

.. code:: python

from tri.declarative import creation_ordered

@creation_ordered
class Thing(object):
pass

t1 = Thing()
t2 = Thing()
t3 = Thing()

assert sorted([t2, t3, t1]) == [t1, t2, t3]


Real world use-case
-------------------

Below is a more complete example of using @declarative:

.. code:: python

from tri.declarative import declarative, creation_ordered


@creation_ordered
class Field(object):
pass


class IntField(Field):
def render(self, value):
return '%s' % value


class StringField(Field):
def render(self, value):
return "'%s'" % value


@declarative(Field, 'table_fields')
class SimpleSQLModel(object):

def __init__(self, **kwargs):
self.table_fields = kwargs.pop('table_fields')

for name in kwargs:
assert name in self.table_fields
setattr(self, name, kwargs[name])

def insert_statement(self):
return 'INSERT INTO %s(%s) VALUES (%s)' % (self.__class__.__name__,
', '.join(self.table_fields.keys()),
', '.join([field.render(getattr(self, name))
for name, field in self.table_fields.items()]))


class User(SimpleSQLModel):
username = StringField()
password = StringField()
age = IntField()


my_user = User(username='Bruce_Wayne', password='Batman', age=42)
assert my_user.username == 'Bruce_Wayne'
assert my_user.password == 'Batman'
assert my_user.insert_statement() == "INSERT INTO User(username, password, age) VALUES ('Bruce_Wayne', 'Batman', 42)"

# Fields are ordered by creation time (due to having used the @creation_ordered decorator)
assert my_user.get_meta().table_fields.keys() == ['username', 'password', 'age']


@with_meta
----------

Class decorator to enable a class (and it's sub-classes) to have a 'Meta' class attribute.

The members of the Meta class will be injected as arguments to constructor calls. e.g.:

.. code:: python

from tri.declarative import with_meta

@with_meta
class Foo(object):

class Meta:
foo = 'bar'

def __init__(self, foo, buz):
assert foo == 'bar'
assert buz == 'buz'

foo = Foo(buz='buz')

# Members of the 'Meta' class can be accessed thru the get_meta() class method.
assert foo.get_meta() == {'foo': 'bar'}
assert Foo.get_meta() == {'foo': 'bar'}

Foo() # Crashes, has 'foo' parameter, but no has no 'buz' parameter.


The passing of the merged name space to the constructor is optional.
It can be disabled by passing :code:`add_init_kwargs=False` to the decorator.

.. code:: python

from tri.declarative import with_meta

@with_meta(add_init_kwargs=False)
class Foo(object):
class Meta:
foo = 'bar'

Foo() # No longer crashes
assert Foo().get_meta() == {'foo': 'bar'}


Another example:

.. code:: python

from tri.declarative import with_meta

class Foo(object):

class Meta:
foo = 'bar'
bar = 'bar'

@with_meta
class Bar(Foo):

class Meta:
foo = 'foo'
buz = 'buz'

def __init__(self, *args, **kwargs):
assert kwargs['foo'] == 'foo' # from Bar (overrides Foo)
assert kwargs['bar'] == 'bar' # from Foo
assert kwargs['buz'] == 'buz' # from Bar


This can be used e.g to enable sub-classes to modify constructor default arguments.


=========
Changelog
=========

Here's the recent changes to tri.declarative.

.. changelog::
:version: dev
:released: Ongoing

.. change::
:tags: docs

Updated CHANGES.