implement __hash__() in OverrideRule to easily identify uniqueness

docs/intro/overrides.rst

@@ -547,6 +547,10 @@ packages** in your project, you can do it like:
     # 3. OverrideRule(for_patterns=Patterns(include=['site_2.com'], exclude=[], priority=500), use=<class 'gadget_sites_page_objects.site_2.GadgetSite2'>, instead_of=<class 'gadget_sites_page_objects.GadgetGenericPage'>, meta={})
     # 4. OverrideRule(for_patterns=Patterns(include=['site_3.com'], exclude=[], priority=500), use=<class 'gadget_sites_page_objects.site_3.GadgetSite3'>, instead_of=<class 'gadget_sites_page_objects.GadgetGenericPage'>, meta={})
 
+    # If there are any duplicates when combining the OverrideRules,
+    # you could do the following to ensure uniqueness:
+    combined_rules = set(combined_registry)
+
 .. note::
 
     Note that ``registry.get_overrides() == list(registry.data.values())``. We're

tests/test_overrides.py

@@ -17,11 +17,35 @@
     PONestedModuleOverridenSecondary,
 )
 from web_poet import PageObjectRegistry, default_registry, registry_pool
+from web_poet.overrides import OverrideRule
 
 
 POS = {POTopLevel1, POTopLevel2, POModule, PONestedPkg, PONestedModule}
 
 
+def test_override_rule_uniqueness():
+    """The same instance of an OverrideRule with the same attribute values should
+    have the same hash identity.
+    """
+
+    patterns = Patterns(include=["example.com"], exclude=["example.com/blog"])
+
+    rule1 = OverrideRule(
+        for_patterns=patterns,
+        use=POTopLevel1,
+        instead_of=POTopLevelOverriden2,
+        meta={"key_1": 1}
+    )
+    rule2 = OverrideRule(
+        for_patterns=patterns,
+        use=POTopLevel1,
+        instead_of=POTopLevelOverriden2,
+        meta={"key_2": 2}
+    )
+
+    assert hash(rule1) == hash(rule2)
+
+
 def test_list_page_objects_all():
     rules = default_registry.get_overrides()
     page_objects = {po.use for po in rules}

web_poet/overrides.py

@@ -15,13 +15,26 @@
 @dataclass
 class OverrideRule:
     """A single override rule that specifies when a Page Object should be used
-    instead of another."""
+    instead of another.
+    """
 
     for_patterns: Patterns
     use: Callable
     instead_of: Callable
     meta: Dict[str, Any] = field(default_factory=dict)
 
+    def __hash__(self):
+        # TODO: Remove this when the following has been implemented:
+        #   - https://github.com/zytedata/url-matcher/issues/3
+        pattern_hash = hash(
+            (
+                tuple(self.for_patterns.include),
+                tuple(self.for_patterns.exclude),
+                self.for_patterns.priority,
+            )
+        )
+        return hash((pattern_hash, self.use, self.instead_of))
+
 
 def _as_list(value: Optional[Strings]) -> List[str]:
     """