instruct 0.6.7

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A compact, fast object system that can serve as the basis for a DAO model.

To that end, instruct uses __slots__ to prevent new attribute addition, properties to control types, event listeners and historical changes, and a Jinja2-driven codegen to keep a pure-Python implementation as fast and as light as possible.

I want to basically have a form of strictly typed objects that behave like C structs but can handle automatically coercing incoming values correctly, have primitive events and have fast __iter__, __eq__ while also allowing for one to override it in the final class (and even call super!)

This girl asks for a lot but I like taking metaclassing as far as it can go without diving into using macropy. 😉

Current Capabilities:

• Support multiple inheritance, chained fields and __slots__ [Done]

• Support type coercions (via _coerce__) [Done]

• Strictly-typed ability to define fixed data objects [Done]

• Ability to drop all of the above type checks [Done]

• Track changes made to the object as well as reset [Done]

• Fast __iter__ [Done]

• Native support of pickle [Done]/json [Done]

• Support List[type] declarations and initializations [Done]

• optionally data class annotation-like behavior [Done]

• _asdict, _astuple, _aslist functions like in a NamedTuple [Done]

• get, keys, values, item functions available in the module and in a mixin named mapping=True

  • This effectively allows access like other packages e.g. attrs.keys(item_instance)

• bytes/bytearray are urlsafe base64 encoded by default, can override per field via a class level BINARY_JSON_ENCODERS = {key: encoding_function} [Done]

• Allow __coerce__ to have a tuple of field names to avoid repetition on __coerce__ definitions [Done]

• Allow use of Literal in the type (exact match of a value to a vector of values) [Done]

• Allow subtraction of properties like (F - {"a", "b"}).keys() == F_without_a_b.keys() [Done]

  • This will allow one to slim down a class to a restricted subtype, like for use in a DAO system to load/hold less data.

• Allow subtraction of properties like (F - {"a": {"b"}).keys() == F_a_without_b.keys() [Done]

  • This allows for one to remove fields that are unused prior to class initialization.

• Allow subtraction of properties via an inclusive list like (F & {"a", "b"}).keys() == F_with_only_a_and_b.keys() [Done]

• Allow subtraction to propagate to embedded Instruct classes like (F - {"a.b", "a.c"}).a.keys() == (F_a.keys() - {"b", "c")) [Done]

  • This would really allow for complex trees of properties to be rendered down to thin SQL column selects, thus reducing data load.

• Replace references to an embedded class in a __coerce__ function with the subtracted form in case of embedded property subtractions [Done]

Next Goals:

• Allow Generics i.e. class F(instruct.Base, T): ... -> F[str](...)

  • Would be able to allow specialized subtypes

• Allow use of Annotated i.e. field: Annotated[int, NoJSON, NoPickle] and have to_json and pickle.dumps(...) skip “field”

  • Would grant a more powerful interface to controlling code-gen’ed areas

• CStruct-Base class that operates on an _cvalue cffi struct.

• Cython compatibility

Design Goal

This comes out of my experience of doing multiple object systems mean to represent database relations and business rules. One thing that has proven an issue is the requirements for using as little memory as possible, as little CPU as possible yet prevent the developer from trying to stick a string where a integer belongs.

Further complicating this model is that desire to “correct” data as it comes in. Done correctly, it is possible to feed an instruct.Base-derived class fields that are not of the correct data type but are eligible for being coerced (converted) into the right type with a function. With some work, it’ll be possible to inline a lambda val: ... expression directly into the setter function code.

Finally, multiple inheritance is a must. Sooner or later, you end up making a single source implementation for a common behavior shared between objects. Being able to share business logic between related implementations is a wonderful thing.

Wouldn’t it be nice to define a heirachy like this:

class Member(Base):
    __slots__ = {
        'first_name': str,
        'last_name': str,
        'id': str,
    }
    def __init__(self, **kwargs):
        self.first_name = self.last_name = ''
        self.id = -1
        super().__init__(**kwargs)

class Organization(Base, history=True):
    # ARJ: Note how we can also use the dataclass/typing.NamedTuple
    # definition format and it behaves just like the ``__slots__`` example
    # above!
    name: str
    id: int
    members: List[Member]
    created_date: datetime.datetime
    secret: Annotated[str, NoJSON, NoPickle, NoIterable]

    __coerce__ = {
        'created_date': (str, lambda obj: datetime.datetime.strptime('%Y-%m-%d', obj))
    }

    def __init__(self, **kwargs):
        self.name = ''
        self.id = -1
        self.members = []
        self.created_date = datetime.datetime.utcnow()
        super().__init__(**kwargs)

And have it work like this?

data = {
    "name": "An Org",
    "id": 123,
    "members": [
        {
            "id": 551,
            "first_name": "Jinja",
            "last_name": "Ninja",
        }
    ]
}
org = Organization(secret="my secret", **data)
assert org.members[0].first_name == 'Jinja'
assert org.secret == "my secret"
org.name = "New Name"
org.history()
assert not any(y == "my secret" for y in tuple(org))
assert Organization.to_json(org) == data

Example Usage

>>> from instruct import Base
>>>
>>> class MyClass(Base):
...     foo: int
...     bar: Optional[str]
...     baz: Union[Dict[str, str], int]
...     def __eq__(self, other):
...         if isinstance(other, tuple) and len(other) == 3:
...            # Cast the tuple to this type!
...            other = MyClass(*other)
...         return super().__eq__(other)
...
>>> instance = MyClass(1, None, baz={"a": "a"})
>>> assert instance.foo == 1
>>> assert instance.bar is None
>>> instance.bar = "A String!"
>>>
>>> assert instance == (1, "A String!", {"a": "a"})
>>>
>>> instance.foo = 'I should not be allowed'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<getter-setter>", line 36, in _set_foo
TypeError: Unable to set foo to 'I should not be allowed' (str). foo expects a int
>>>

Design

Solving the multiple-inheritance and __slots__ problem

Consider the following graph:

Base1    Base2
     \  /
   Class A

If both defined __slots__ = (), Class A would be able to declare __slots__ to hold variables. For now on, we shall consider both Base’s to have __slots__ = () for simplicity.

However, consider this case:

Base1    Base2
     \  /
   Class A     Class B
          \    /
          Class C

Now this isn’t possible if Class A has non-empty __slots__.

But what if we could change the rules. What if, somehow, when you __new__ ed a class, it really gave you a specialized form of the class with non-empty __slots__?

Such a graph may look like this:

Base1    Base2
     \  /
   Class A     Class B
      |  \    /     |
Class _A  Class C  Class _B
            |
          Class _C

Now it is possible for any valid multiple-inheritance chain to proceed, provided it respects the above constraints - there are either support classes or data classes (denoted with an underscore in front of their class name). Support classes may be inherited from, data classes cannot.

Solving the Slowness issue

I’ve noticed that there are constant patterns of writing setters/getters and other related functions. Using Jinja2, we can rely on unhygenic macros while preserving some semblance of approachability. It’s more likely a less experienced developer could handle blocks of Jinja-fied Python than AST synthesis/traversal.

Callgraph Performance

Release Process

$ rm -rf dist/* && python -m pytest tests/ && python setup.py sdist bdist_wheel && twine upload dist/*

Benchmark

Latest benchmark run::

(python) Fateweaver:~/software/instruct [master]$ python --version
Python 3.7.7
(python) Fateweaver:~/software/instruct [master]$ python -m instruct benchmark
Overhead of allocation, one field, safeties on: 19.53us
Overhead of allocation, one field, safeties off: 19.50us
Overhead of setting a field:
Test with safeties: 0.27 us
Test without safeties: 0.17 us
Overhead of clearing/setting
Test with safeties: 0.75 us
Test without safeties: 0.65 us
(python) Fateweaver:~/software/instruct [master]$

Before additions of coercion, event-listeners, multiple-inheritance

$ python -m instruct benchmark
Overhead of allocation, one field, safeties on: 6.52us
Overhead of allocation, one field, safeties off: 6.13us
Overhead of setting a field:
Test with safeties: 0.40 us
Test without safeties: 0.22 us
Overhead of clearing/setting
Test with safeties: 1.34 us
Test without safeties: 1.25 us

After additions of those. Safety is expensive.

$ python -m instruct benchmark
Overhead of allocation, one field, safeties on: 19.25us
Overhead of allocation, one field, safeties off: 18.98us
Overhead of setting a field:
Test with safeties: 0.36 us
Test without safeties: 0.22 us
Overhead of clearing/setting
Test with safeties: 1.29 us
Test without safeties: 1.14 us