Adds proper implementation of Lookup.get_default()

Author: AxelVoitier

CHANGELOG.md

@@ -7,6 +7,7 @@ CHANGELOG
 - Adds a EntryPointLookup.
 - Adds a DelegatedLookup.
 - Adds a ProxyLookup.
+- Adds a proper resolution for system default lookup Lookup.get_default().
 - Fixes issue with listeners registration disappearing immediately when using object-bound methods.
 - Content of a GenericLookup can now behave like a Container (ie. you can do things like "obj in content").
 - When an instance is not hashable, provides an alternative using id() of the object in order to be

README.md

@@ -91,6 +91,7 @@ my_content.remove(child1)
 
 ## Other lookups
 
+* `lookups.Lookup.get_default()`: The default lookup in a system.
 * `lookups.ProxyLookup`: A lookup that merge results from several lookups.
 * `lookups.DelegatedLookup`: A lookup that redirects to another (dynamic) lookup, through a LookupProvider.
 * `lookups.EntryPointLookup`: A lookup loading its instances from a setuptools entry point group (ie. provided by any installed package).

lookups/lookup.py

@@ -24,25 +24,66 @@ class Lookup(ABC):
     A general registry permitting clients to find instances of services (implementation of a given
     interface).
 
-    This class is inspired Netbeans Platform lookup mechanism. The Lookup API concentrates on the
+    This class is inspired by Netbeans Platform lookup mechanism. The Lookup API concentrates on the
     lookup, not on the registration.
     '''
 
+    _DEFAULT_LOOKUP: Lookup = None  # type: ignore
+    _DEFAULT_LOOKUP_PROVIDER: LookupProvider = None  # type: ignore
+    _DEFAULT_ENTRY_POINT_GROUP = 'lookup.default'
+
     @classmethod
     def get_default(cls) -> Lookup:
         '''
         Method to obtain the global lookup in the whole system.
 
         The actual returned implementation can be different in different systems, but the default
-        one is based on lookup.Lookups.???.
+        one is based on lookups.ProxyLookup.
+
+        The resolution is the following:
+        - If there is already a default lookup provider defined, returns its lookup.
+        - If there is already a default lookup defined, returns it.
+        - Loads on EntryPointLookup on 'lookup.default' group:
+          - If it finds a lookup which happens to also be a lookup provider, returns its lookup.
+          - If it finds a lookup, returns it.
+          - If it finds a lookup provider, returns DelegatedLookup from it.
+        - Otherwise, returns a ProxyLookup with just the EntryPointLookup as source.
 
         :return: The global lookup in the system
         :rtype: Lookup
         '''
-        # Temporary solution
-        from .generic_lookup import GenericLookup
-        from .instance_content import InstanceContent
-        return GenericLookup(InstanceContent())
+
+        if (cls._DEFAULT_LOOKUP is not None) or (cls._DEFAULT_LOOKUP_PROVIDER is not None):
+            if cls._DEFAULT_LOOKUP_PROVIDER is not None:
+                lookup = cls._DEFAULT_LOOKUP_PROVIDER.get_lookup()
+                if lookup is not None:
+                    return lookup
+
+            return cls._DEFAULT_LOOKUP
+
+        from .entry_point import EntryPointLookup
+        epl = EntryPointLookup(cls._DEFAULT_ENTRY_POINT_GROUP)
+        cls._DEFAULT_LOOKUP = epl.lookup(Lookup)
+        if cls._DEFAULT_LOOKUP is not None:
+            if isinstance(cls._DEFAULT_LOOKUP, LookupProvider):
+                cls._DEFAULT_LOOKUP_PROVIDER = cls._DEFAULT_LOOKUP
+                lookup = cls._DEFAULT_LOOKUP_PROVIDER.get_lookup()
+                if lookup is not None:
+                    return lookup
+
+            return cls._DEFAULT_LOOKUP
+
+        provider = epl.lookup(LookupProvider)
+        if provider is not None:
+            from .delegated_lookup import DelegatedLookup
+            cls._DEFAULT_LOOKUP = DelegatedLookup(provider)
+
+            return cls._DEFAULT_LOOKUP
+
+        from .proxy_lookup import ProxyLookup
+        cls._DEFAULT_LOOKUP = ProxyLookup(epl)
+
+        return cls._DEFAULT_LOOKUP
 
     @abstractmethod
     def lookup(self, cls: Type[object]) -> Optional[object]:

setup.cfg

@@ -54,10 +54,21 @@ dev =
     check-manifest
 
 [options.entry_points]
-lookup.tests =
+lookups.test_entry_point =
     parent = tests.tools:TestParentObject
     child = tests.tools:TestChildObject
     other = tests.tools:TestOtherObject
+lookups.test_default_lookup =
+    a_lookup = tests.test_lookup_default:DefaultLookup
+lookups.test_default_lookup_lookup_provider =
+    a_lookup = tests.test_lookup_default:DefaultLookupLookupProvider
+lookups.test_default_lookup_provider =
+    a_lookup = tests.test_lookup_default:DefaulLookupProvider
+lookups.test_default_no_lookup =
+    parent = tests.tools:TestParentObject
+    child = tests.tools:TestChildObject
+    other = tests.tools:TestOtherObject
+lookups.test_default_empty_entry_point_group =
 
 [flake8]
 max-line-length = 100

tests/test_entry_point.py

@@ -51,7 +51,7 @@ def check_item(expected_classes, item):
 
 
 def test_instantiation():
-    assert EntryPointLookup('lookup.tests')
+    assert EntryPointLookup('lookups.test_entry_point')
 
 
 def test_non_existant_group():
@@ -60,14 +60,14 @@ def test_non_existant_group():
 
 @pytest.mark.parametrize('search, expected_classes', MEMBER_FIXTURES)
 def test_lookup(search, expected_classes):
-    lookup = EntryPointLookup('lookup.tests')
+    lookup = EntryPointLookup('lookups.test_entry_point')
 
     assert isinstance(lookup.lookup(search), expected_classes)
 
 
 @pytest.mark.parametrize('search, expected_classes', MEMBER_FIXTURES)
 def test_lookup_item(search, expected_classes):
-    lookup = EntryPointLookup('lookup.tests')
+    lookup = EntryPointLookup('lookups.test_entry_point')
 
     item = lookup.lookup_item(search)
     check_item(expected_classes, item)
@@ -76,15 +76,15 @@ def test_lookup_item(search, expected_classes):
 
 @pytest.mark.parametrize('search, expected_classes', MEMBER_FIXTURES)
 def test_lookup_all(search, expected_classes):
-    lookup = EntryPointLookup('lookup.tests')
+    lookup = EntryPointLookup('lookups.test_entry_point')
 
     all_instances = lookup.lookup_all(search)
     check_all_instances(expected_classes, all_instances)
 
 
 @pytest.mark.parametrize('search, expected_classes', MEMBER_FIXTURES)
 def test_lookup_result(search, expected_classes):
-    lookup = EntryPointLookup('lookup.tests')
+    lookup = EntryPointLookup('lookups.test_entry_point')
     if not isinstance(expected_classes, Sequence):
         expected_classes = (expected_classes, )
 
@@ -110,7 +110,7 @@ def test_lookup_result(search, expected_classes):
 
 @pytest.mark.parametrize('search, expected_classes', MEMBER_FIXTURES)
 def test_listeners(search, expected_classes):
-    lookup = EntryPointLookup('lookup.tests')
+    lookup = EntryPointLookup('lookups.test_entry_point')
 
     result = lookup.lookup_result(search)
 

tests/test_lookup_default.py

@@ -0,0 +1,141 @@
+# -*- coding: utf-8 -*-
+# Copyright (c) 2021 Contributors as noted in the AUTHORS file
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# System imports
+
+# Third-party imports
+import pytest
+
+# Local imports
+from lookups import Lookup, LookupProvider, DelegatedLookup, ProxyLookup
+from lookups.singleton import SingletonLookup
+from .tools import TestParentObject, TestChildObject, TestOtherObject
+
+
+class DefaultLookup(SingletonLookup):
+
+    def __init__(self):
+        super().__init__(TestParentObject())
+
+
+class DefaulLookupProvider(LookupProvider):
+
+    def get_lookup(self):
+        return SingletonLookup(TestParentObject())
+
+
+class DefaultLookupLookupProvider(SingletonLookup, LookupProvider):
+
+    def __init__(self):
+        super().__init__(TestOtherObject())
+        self._lookup = SingletonLookup(TestParentObject())
+
+    def get_lookup(self):
+        return self._lookup
+
+
+@pytest.fixture
+def cleanup():
+    Lookup._DEFAULT_LOOKUP = None
+    Lookup._DEFAULT_LOOKUP_PROVIDER = None
+    Lookup._DEFAULT_ENTRY_POINT_GROUP = 'lookup.default'
+
+    yield
+
+    Lookup._DEFAULT_LOOKUP = None
+    Lookup._DEFAULT_LOOKUP_PROVIDER = None
+    Lookup._DEFAULT_ENTRY_POINT_GROUP = 'lookup.default'
+
+
+def test_default_lookup(cleanup):
+    Lookup._DEFAULT_ENTRY_POINT_GROUP = 'lookups.test_default_lookup'
+    dflt = Lookup.get_default()
+    assert dflt
+    assert isinstance(dflt, DefaultLookup)
+
+    all_instances = dflt.lookup_all(object)
+    assert len(all_instances) == 1
+    assert isinstance(all_instances[0], TestParentObject)
+
+    assert Lookup.get_default() is dflt
+
+    assert Lookup._DEFAULT_LOOKUP is dflt
+    assert Lookup._DEFAULT_LOOKUP_PROVIDER is None
+
+
+def test_default_lookup_lookup_provider(cleanup):
+    Lookup._DEFAULT_ENTRY_POINT_GROUP = 'lookups.test_default_lookup_lookup_provider'
+    dflt = Lookup.get_default()
+    assert dflt
+    assert isinstance(dflt, SingletonLookup)
+
+    all_instances = dflt.lookup_all(object)
+    assert len(all_instances) == 1
+    assert isinstance(all_instances[0], TestParentObject)
+
+    assert Lookup.get_default() is dflt
+
+    assert isinstance(Lookup._DEFAULT_LOOKUP, DefaultLookupLookupProvider)
+    assert Lookup._DEFAULT_LOOKUP_PROVIDER is Lookup._DEFAULT_LOOKUP
+
+    # Try have the provider return None
+    Lookup._DEFAULT_LOOKUP_PROVIDER._lookup = None
+    new_dflt = Lookup.get_default()
+    assert new_dflt is Lookup._DEFAULT_LOOKUP
+
+    all_instances = new_dflt.lookup_all(object)
+    assert len(all_instances) == 1
+    assert isinstance(all_instances[0], TestOtherObject)
+
+
+def test_default_lookup_provider(cleanup):
+    Lookup._DEFAULT_ENTRY_POINT_GROUP = 'lookups.test_default_lookup_provider'
+    dflt = Lookup.get_default()
+    assert dflt
+    assert isinstance(dflt, DelegatedLookup)
+
+    all_instances = dflt.lookup_all(object)
+    assert len(all_instances) == 1
+    assert isinstance(all_instances[0], TestParentObject)
+
+    assert Lookup.get_default() is dflt
+
+    assert Lookup._DEFAULT_LOOKUP is dflt
+    assert Lookup._DEFAULT_LOOKUP_PROVIDER is None
+
+
+def test_default_no_lookup(cleanup):
+    Lookup._DEFAULT_ENTRY_POINT_GROUP = 'lookups.test_default_no_lookup'
+    dflt = Lookup.get_default()
+    assert dflt
+    assert isinstance(dflt, ProxyLookup)
+
+    all_instances = dflt.lookup_all(object)
+    assert all_instances
+    assert (len(all_instances) % 3) == 0  # Because pytest can double up our entry points
+    assert {type(instance) for instance in all_instances} == set([
+        TestParentObject, TestChildObject, TestOtherObject])
+
+    assert Lookup.get_default() is dflt
+
+    assert Lookup._DEFAULT_LOOKUP is dflt
+    assert Lookup._DEFAULT_LOOKUP_PROVIDER is None
+
+
+def test_default_empty_entry_point_group(cleanup):
+    Lookup._DEFAULT_ENTRY_POINT_GROUP = 'lookups.test_default_empty_entry_point_group'
+    dflt = Lookup.get_default()
+    assert dflt
+    assert isinstance(dflt, ProxyLookup)
+
+    all_instances = dflt.lookup_all(object)
+    assert not all_instances
+
+    assert Lookup.get_default() is dflt
+
+    assert Lookup._DEFAULT_LOOKUP is dflt
+    assert Lookup._DEFAULT_LOOKUP_PROVIDER is None