Bundle databackend

Author: nathanjmcdougall

pins/_databackend.py

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+"""See https://github.com/machow/databackend"""
+
+# MIT License
+# Copyright (c) 2024 databackend contributors
+# See pins/tests/_databackend/LICENSE
+# commit 214832b, on 31/07/2024, v0.0.2+dev
+
+import importlib
+import sys
+from abc import ABCMeta
+
+
+def _load_class(mod_name: str, cls_name: str):
+    mod = importlib.import_module(mod_name)
+    return getattr(mod, cls_name)
+
+
+class _AbstractBackendMeta(ABCMeta):
+    def register_backend(cls, mod_name: str, cls_name: str):
+        cls._backends.append((mod_name, cls_name))
+        cls._abc_caches_clear()
+
+
+class AbstractBackend(metaclass=_AbstractBackendMeta):
+    @classmethod
+    def __init_subclass__(cls):
+        if not hasattr(cls, "_backends"):
+            cls._backends = []
+
+    @classmethod
+    def __subclasshook__(cls, subclass):
+        for mod_name, cls_name in cls._backends:
+            if mod_name not in sys.modules:
+                # module isn't loaded, so it can't be the subclass
+                # we don't want to import the module to explicitly run the check
+                # so skip here.
+                continue
+            else:
+                parent_candidate = _load_class(mod_name, cls_name)
+                if issubclass(subclass, parent_candidate):
+                    return True
+
+        return NotImplemented

pins/tests/_databackend/LICENSE

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+MIT License
+
+Copyright (c) 2024 databackend contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

pins/tests/_databackend/__init__.py

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+class ADataClass:
+    pass
+
+
+class ADataClass2:
+    pass

pins/tests/_databackend/a_data_class.py

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+class UnimportedClass:
+    pass

pins/tests/_databackend/an_unimported_module.py

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+"""See https://github.com/machow/databackend"""
+
+import importlib
+import sys
+
+import pytest
+
+from pins._databackend import AbstractBackend
+from pins.tests._databackend.a_data_class import ADataClass, ADataClass2
+
+CLASS_MOD = "pins.tests._databackend.a_data_class"
+CLASS_NAME = "ADataClass"
+
+
+@pytest.fixture
+def Base():
+    class Base(AbstractBackend):
+        pass
+
+    Base.register_backend(CLASS_MOD, CLASS_NAME)
+
+    return Base
+
+
+def test_check_unimported_mod(Base):
+    class ABase(AbstractBackend):
+        pass
+
+    mod_name = "pins.tests._databackend.an_unimported_module"
+    ABase.register_backend(mod_name, "UnimportedClass")
+
+    # check pre-import and verify it's still not imported ----
+    assert not issubclass(int, ABase)
+    assert mod_name not in sys.modules
+
+    # do import and verify ABC is seen as parent class ----
+    mod = importlib.import_module(mod_name)
+
+    assert issubclass(mod.UnimportedClass, ABase)
+
+
+def test_issubclass(Base):
+    assert issubclass(ADataClass, Base)
+
+
+def test_isinstance(Base):
+    assert isinstance(ADataClass(), Base)
+
+
+def test_check_is_cached():
+    checks = [0]
+
+    class ABase(AbstractBackend):
+        @classmethod
+        def __subclasshook__(cls, subclass):
+            # increment the number in checks, as a dumb way
+            # of seeing how often this runs
+            # could also use abc.ABCMeta._dump_registry
+            checks[0] = checks[0] + 1
+            return super().__subclasshook__(subclass)
+
+    # this check runs subclasshook ----
+    issubclass(ADataClass, ABase)
+    assert checks[0] == 1
+
+    # now that ADataClass is in the abc.ABCMeta cache, it
+    # does *not* run subclasshook
+    issubclass(ADataClass, ABase)
+    assert checks[0] == 1
+
+
+def test_backends_spec_at_class_declaration():
+    class ABase(AbstractBackend):
+        _backends = [(CLASS_MOD, CLASS_NAME)]
+
+    assert issubclass(ADataClass, ABase)
+
+
+def test_backends_do_not_overlap():
+    class ABase1(AbstractBackend): ...
+
+    class ABase2(AbstractBackend): ...
+
+    ABase1.register_backend(CLASS_MOD, "ADataClass")
+    ABase2.register_backend(CLASS_MOD, "ADataClass2")
+
+    obj1 = ADataClass()
+    obj2 = ADataClass2()
+
+    assert isinstance(obj1, ABase1)
+    assert not isinstance(obj1, ABase2)
+
+    assert not isinstance(obj2, ABase1)
+    assert isinstance(obj2, ABase2)