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

Project description


tri.declarative contains tools that make it easy to write declarative code. This includes:

Class decorators

With just a few lines of code, turn your API from:

quux = Foo(things=[Bar(name='a', param=1), Bar(name='b', param=2), Bar(name='c', param=2)], baz=3)


class Quux(Foo):
    a = Bar(param=1)
    b = Bar(param=2)
    c = Bar(param=2)

    class Meta:
        baz = 3

And you can still use the first style when it’s more convenient!

More detailed usage examples on @declarative below.


d = dict(
    foo=lambda x: x*2,
    bar=lambda y: y+5,
        foo=lambda x: x*6,

# evaluate only one level
assert evaluate(d, x=2) == dict(
    bar=lambda y: y+5,  # this function doesn't match the signature so isn't evaluated
        foo=lambda x: x*6,  # one level down so isn't evaluated

# evaluate recursively
assert evaluate_recursive(d, x=2) == dict(
    bar=lambda y: y+5,  # this function doesn't match the signature so isn't evaluated


d = dict(

assert filter_show_recursive(d) == dict(

Keyword argument dispatching


def foo(bar, baz):

Get/set attribute given a path string

class Foo(object):
    def __init__(a):
        self.a = a

class Bar(object):
    def __init__(b):
        self.b = b

class Baz(object):
    def __init__(c):
        self.c = c

x = Foo(Bar(Baz(c=3)))

assert getattr_path(x, 'a__b__c') == 3

assert setattr_path(x, 'a__b__c', 10)
assert getattr_path(x, 'a__b__c') == 10

Running tests

You need tox installed then just make test.





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

from tri.declarative import declarative

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 members argument will also be collected from sub-classes:

from tri.declarative import declarative

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 members argument can be given another name (things in the example below).

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 OrderedDict and will be ordered by class inheritance and by using sorted of the values within each class. (In the ‘str’ example, 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.

from tri.declarative import declarative

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')


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 @declarative class when member order matters.

from tri.declarative import creation_ordered

class Thing(object):

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:

from tri.declarative import declarative, creation_ordered

class Field(object):

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 list(my_user.get_declared('table_fields').keys()) == ['username', 'password', 'age']


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.:

from tri.declarative import 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 add_init_kwargs=False to the decorator.

from tri.declarative import with_meta

class Foo(object):
    class Meta:
        foo = 'bar'

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

Another example:

from tri.declarative import with_meta

class Foo(object):

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

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.


2.0.0 (2019-04-12)

  • Fixed get_signature cache to not pollute struct-like dicts
  • New call_target semantics for class method shortcuts, this is a potential breaking change

1.2.1 (2019-13-15)

  • Improved documentation output

1.2.0 (2019-13-14)

  • Add get_members function to enable reuse of @declarative attribute collection
  • Add @class_shortcut decorator to enable @with_meta aware class shortcuts

1.1.0 (2018-11-22)

  • Added generate_rst_docs function.

1.0.6 (2018-09-28)

  • Shortcut is now a special case when merging Namespace objects. When already in a Namespace, a Shortcut now get overwritten by setitem_path(), not merged into the written value.

1.0.5 (2018-09-21)

  • Fix broken handling of empty key

1.0.4 (2018-09-21)

  • Cleanup Namespace path logic and make sure it is symmetrical and tested.
  • Added deprecation warning on string to dict promotion on namespace merge.

1.0.3 (2018-06-26)

  • Fixed release functionality

1.0.2 (2018-06-18)

  • Don’t support RefinableObject in evaluate_recursive. This was a mistake.

1.0.1 (2018-06-15)

  • Support RefinableObject in evaluate_recursive.

1.0.0 (2018-05-23)

  • Cleanup deprecation warnings from inspect.getargspec

0.34.0 (2017-08-21)

  • Fix bug in 0.33.0 when promoting callable to Namespace.

0.33.0 (2017-08-21)

  • Fix bug when promoting callable to Namespace.
  • Fix handling of EMPTY marker.

0.32.0 (2017-07-04)

  • Added promoting callable namespace members to Namespace with call_target in setdefaults_path.

0.31.0 (2017-06-15)

  • Improve sort_after to allow more combinations of after=… specifications. e.g. by name of an entry also moved by spec.
  • Changed name of first parameter of setdefaults_path to __target__ to avoid collitions with namespace parameters.
  • Added RefinableObject base for reuse by classes wanting to be able to be configured via constructor kwarg parameters in a declarative fashion. (The namespace of possible constructor overrides are declared with Refinable() for values and the decorator @refinable for methods.
  • Added first incarnation of crawling the definitions to recursively find available parameters on objects and their aggregates.
  • Added Shortcut abstraction to be able to find pre-defined set of overrides of RefinableObject classes.

0.30.0 (2017-02-10)

  • evaluate and evaluate_recursive also works for methods as well as for functions.

0.29.0 (2016-09-12)

  • Fixed loop detection in flatten for Namespaces. This resulted in data corruption.

0.28.0 (2016-07-15)

  • Added Namespace subclass of tri.struct.Struct to explicit capture the path splitting semantics. (And added method for flattening a Namespace back to path notation.)

0.27.0 (2016-07-13)

  • Fix bug in evaluate signature detection with optional arguments. (lambda a, b=17: a+b was correctly matched but lambda b, a=17: a+b was not)

0.26.0 (2016-05-06)

  • Added EMPTY marker to setdefaults_path to avoid mixup when empty dict is provided in function defaults.

0.25.0 (2016-04-28)

  • Added @dispatch decorator

0.24.0 (2016-04-20)

  • Fix bug in setdefault_path tripping up on key ordering.
  • Dropped namespace_factory keyword argument to setdefaults_path not likely ever beeing used.

0.23.0 (2016-04-15)

  • setdefaults_path now accepts multiple default dicts. (To simplify the pattern of shortcuts in tri.form, tri.query and tri.table where we now will end up with: new_kwargs = setdefaults_path(Struct(), kwargs, dict(….))

0.22.0 (2016-03-24)

  • sort_after() should produce an error when attempting to sort after non-existant keys
  • Tweaked namespace merge in setdefaults_path

0.21.0 (2016-03-01)

  • Fix corner case in collect_namespaces where one parameter imply a value and others imply a namespace.
  • Added setdefaults_path helper with __ namespace traversal.

0.20.0 (2016-02-29)

  • Added assert_kwargs_not_empty convenience function.
  • Improved documentation.

0.19.0 (2016-01-12)

  • When making instances of a class decorated with @declarative the declared values are copied (shallow) before being passed to __init__.
  • Instances will get an own copy of the declared attributes written to their __dict__

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