tests/test_slots.py

"""
Unit tests for slot-related functionality.
"""

import pytest

import attr

from attr._compat import PY2, PYPY, just_warn, make_set_closure_cell


# Pympler doesn't work on PyPy.
try:
    from pympler.asizeof import asizeof

    has_pympler = True
except BaseException:  # Won't be an import error.
    has_pympler = False


@attr.s
class C1(object):
    x = attr.ib(validator=attr.validators.instance_of(int))
    y = attr.ib()

    def method(self):
        return self.x

    @classmethod
    def classmethod(cls):
        return "clsmethod"

    @staticmethod
    def staticmethod():
        return "staticmethod"

    if not PY2:

        def my_class(self):
            return __class__  # NOQA: F821

        def my_super(self):
            """Just to test out the no-arg super."""
            return super().__repr__()


@attr.s(slots=True, hash=True)
class C1Slots(object):
    x = attr.ib(validator=attr.validators.instance_of(int))
    y = attr.ib()

    def method(self):
        return self.x

    @classmethod
    def classmethod(cls):
        return "clsmethod"

    @staticmethod
    def staticmethod():
        return "staticmethod"

    if not PY2:

        def my_class(self):
            return __class__  # NOQA: F821

        def my_super(self):
            """Just to test out the no-arg super."""
            return super().__repr__()


def test_slots_being_used():
    """
    The class is really using __slots__.
    """
    non_slot_instance = C1(x=1, y="test")
    slot_instance = C1Slots(x=1, y="test")

    assert "__dict__" not in dir(slot_instance)
    assert "__slots__" in dir(slot_instance)

    assert "__dict__" in dir(non_slot_instance)
    assert "__slots__" not in dir(non_slot_instance)

    assert set(["x", "y"]) == set(slot_instance.__slots__)

    if has_pympler:
        assert asizeof(slot_instance) < asizeof(non_slot_instance)

    non_slot_instance.t = "test"
    with pytest.raises(AttributeError):
        slot_instance.t = "test"

    assert 1 == non_slot_instance.method()
    assert 1 == slot_instance.method()

    assert attr.fields(C1Slots) == attr.fields(C1)
    assert attr.asdict(slot_instance) == attr.asdict(non_slot_instance)


def test_basic_attr_funcs():
    """
    Comparison, `__eq__`, `__hash__`, `__repr__`, `attrs.asdict` work.
    """
    a = C1Slots(x=1, y=2)
    b = C1Slots(x=1, y=3)
    a_ = C1Slots(x=1, y=2)

    # Comparison.
    assert b > a

    assert a_ == a

    # Hashing.
    hash(b)  # Just to assert it doesn't raise.

    # Repr.
    assert "C1Slots(x=1, y=2)" == repr(a)

    assert {"x": 1, "y": 2} == attr.asdict(a)


def test_inheritance_from_nonslots():
    """
    Inheritance from a non-slot class works.

    Note that a slots class inheriting from an ordinary class loses most of the
    benefits of slots classes, but it should still work.
    """

    @attr.s(slots=True, hash=True)
    class C2Slots(C1):
        z = attr.ib()

    c2 = C2Slots(x=1, y=2, z="test")

    assert 1 == c2.x
    assert 2 == c2.y
    assert "test" == c2.z

    c2.t = "test"  # This will work, using the base class.

    assert "test" == c2.t

    assert 1 == c2.method()
    assert "clsmethod" == c2.classmethod()
    assert "staticmethod" == c2.staticmethod()

    assert set(["z"]) == set(C2Slots.__slots__)

    c3 = C2Slots(x=1, y=3, z="test")

    assert c3 > c2

    c2_ = C2Slots(x=1, y=2, z="test")

    assert c2 == c2_

    assert "C2Slots(x=1, y=2, z='test')" == repr(c2)

    hash(c2)  # Just to assert it doesn't raise.

    assert {"x": 1, "y": 2, "z": "test"} == attr.asdict(c2)


def test_nonslots_these():
    """
    Enhancing a non-slots class using 'these' works.

    This will actually *replace* the class with another one, using slots.
    """

    class SimpleOrdinaryClass(object):
        def __init__(self, x, y, z):
            self.x = x
            self.y = y
            self.z = z

        def method(self):
            return self.x

        @classmethod
        def classmethod(cls):
            return "clsmethod"

        @staticmethod
        def staticmethod():
            return "staticmethod"

    C2Slots = attr.s(
        these={"x": attr.ib(), "y": attr.ib(), "z": attr.ib()},
        init=False,
        slots=True,
        hash=True,
    )(SimpleOrdinaryClass)

    c2 = C2Slots(x=1, y=2, z="test")
    assert 1 == c2.x
    assert 2 == c2.y
    assert "test" == c2.z
    with pytest.raises(AttributeError):
        c2.t = "test"  # We have slots now.

    assert 1 == c2.method()
    assert "clsmethod" == c2.classmethod()
    assert "staticmethod" == c2.staticmethod()

    assert set(["x", "y", "z"]) == set(C2Slots.__slots__)

    c3 = C2Slots(x=1, y=3, z="test")
    assert c3 > c2
    c2_ = C2Slots(x=1, y=2, z="test")
    assert c2 == c2_

    assert "SimpleOrdinaryClass(x=1, y=2, z='test')" == repr(c2)

    hash(c2)  # Just to assert it doesn't raise.

    assert {"x": 1, "y": 2, "z": "test"} == attr.asdict(c2)


def test_inheritance_from_slots():
    """
    Inheriting from an attr slot class works.
    """

    @attr.s(slots=True, hash=True)
    class C2Slots(C1Slots):
        z = attr.ib()

    @attr.s(slots=True, hash=True)
    class C2(C1):
        z = attr.ib()

    c2 = C2Slots(x=1, y=2, z="test")
    assert 1 == c2.x
    assert 2 == c2.y
    assert "test" == c2.z

    assert set(["z"]) == set(C2Slots.__slots__)

    assert 1 == c2.method()
    assert "clsmethod" == c2.classmethod()
    assert "staticmethod" == c2.staticmethod()

    with pytest.raises(AttributeError):
        c2.t = "test"

    non_slot_instance = C2(x=1, y=2, z="test")
    if has_pympler:
        assert asizeof(c2) < asizeof(non_slot_instance)

    c3 = C2Slots(x=1, y=3, z="test")
    assert c3 > c2
    c2_ = C2Slots(x=1, y=2, z="test")
    assert c2 == c2_

    assert "C2Slots(x=1, y=2, z='test')" == repr(c2)

    hash(c2)  # Just to assert it doesn't raise.

    assert {"x": 1, "y": 2, "z": "test"} == attr.asdict(c2)


def test_bare_inheritance_from_slots():
    """
    Inheriting from a bare attr slot class works.
    """

    @attr.s(init=False, cmp=False, hash=False, repr=False, slots=True)
    class C1BareSlots(object):
        x = attr.ib(validator=attr.validators.instance_of(int))
        y = attr.ib()

        def method(self):
            return self.x

        @classmethod
        def classmethod(cls):
            return "clsmethod"

        @staticmethod
        def staticmethod():
            return "staticmethod"

    @attr.s(init=False, cmp=False, hash=False, repr=False)
    class C1Bare(object):
        x = attr.ib(validator=attr.validators.instance_of(int))
        y = attr.ib()

        def method(self):
            return self.x

        @classmethod
        def classmethod(cls):
            return "clsmethod"

        @staticmethod
        def staticmethod():
            return "staticmethod"

    @attr.s(slots=True, hash=True)
    class C2Slots(C1BareSlots):
        z = attr.ib()

    @attr.s(slots=True, hash=True)
    class C2(C1Bare):
        z = attr.ib()

    c2 = C2Slots(x=1, y=2, z="test")
    assert 1 == c2.x
    assert 2 == c2.y
    assert "test" == c2.z

    assert 1 == c2.method()
    assert "clsmethod" == c2.classmethod()
    assert "staticmethod" == c2.staticmethod()

    with pytest.raises(AttributeError):
        c2.t = "test"

    non_slot_instance = C2(x=1, y=2, z="test")
    if has_pympler:
        assert asizeof(c2) < asizeof(non_slot_instance)

    c3 = C2Slots(x=1, y=3, z="test")
    assert c3 > c2
    c2_ = C2Slots(x=1, y=2, z="test")
    assert c2 == c2_

    assert "C2Slots(x=1, y=2, z='test')" == repr(c2)

    hash(c2)  # Just to assert it doesn't raise.

    assert {"x": 1, "y": 2, "z": "test"} == attr.asdict(c2)


@pytest.mark.skipif(PY2, reason="closure cell rewriting is PY3-only.")
class TestClosureCellRewriting(object):
    def test_closure_cell_rewriting(self):
        """
        Slot classes support proper closure cell rewriting.

        This affects features like `__class__` and the no-arg super().
        """
        non_slot_instance = C1(x=1, y="test")
        slot_instance = C1Slots(x=1, y="test")

        assert non_slot_instance.my_class() is C1
        assert slot_instance.my_class() is C1Slots

        # Just assert they return something, and not an exception.
        assert non_slot_instance.my_super()
        assert slot_instance.my_super()

    def test_inheritance(self):
        """
        Slot classes support proper closure cell rewriting when inheriting.

        This affects features like `__class__` and the no-arg super().
        """

        @attr.s
        class C2(C1):
            def my_subclass(self):
                return __class__  # NOQA: F821

        @attr.s
        class C2Slots(C1Slots):
            def my_subclass(self):
                return __class__  # NOQA: F821

        non_slot_instance = C2(x=1, y="test")
        slot_instance = C2Slots(x=1, y="test")

        assert non_slot_instance.my_class() is C1
        assert slot_instance.my_class() is C1Slots

        # Just assert they return something, and not an exception.
        assert non_slot_instance.my_super()
        assert slot_instance.my_super()

        assert non_slot_instance.my_subclass() is C2
        assert slot_instance.my_subclass() is C2Slots

    @pytest.mark.parametrize("slots", [True, False])
    def test_cls_static(self, slots):
        """
        Slot classes support proper closure cell rewriting for class- and
        static methods.
        """
        # Python can reuse closure cells, so we create new classes just for
        # this test.

        @attr.s(slots=slots)
        class C:
            @classmethod
            def clsmethod(cls):
                return __class__  # noqa: F821

        assert C.clsmethod() is C

        @attr.s(slots=slots)
        class D:
            @staticmethod
            def statmethod():
                return __class__  # noqa: F821

        assert D.statmethod() is D

    @pytest.mark.skipif(PYPY, reason="ctypes are used only on CPython")
    def test_missing_ctypes(self, monkeypatch):
        """
        Keeps working if ctypes is missing.

        A warning is emitted that points to the actual code.
        """
        monkeypatch.setattr(attr._compat, "import_ctypes", lambda: None)
        func = make_set_closure_cell()

        with pytest.warns(RuntimeWarning) as wr:
            func()

        w = wr.pop()
        assert __file__ == w.filename
        assert (
            "Missing ctypes.  Some features like bare super() or accessing "
            "__class__ will not work with slots classes.",
        ) == w.message.args

        assert just_warn is func