create page_object_for_item() registry method

tests/test_rules.py

@@ -387,6 +387,28 @@ def test_page_object_for() -> None:
         assert not default_registry.page_object_for(cls("https://example.org"))
 
 
+def test_page_object_for_item() -> None:
+    # This is not associated with any rule.
+    class FakeItem:
+        pass
+
+    method = default_registry.page_object_for_item
+
+    for cls in [str, RequestUrl, ResponseUrl]:
+        url = cls("https://example.com")
+        assert method(url, ProductSimilar) == CustomProductPageNoReturns
+        assert method(url, Product) == CustomProductPageDataTypeOnly
+        assert method(url, ProductSeparate) == SeparateProductPage
+        assert method(url, ProductFewerFields) == LessProductPage
+        assert method(url, ProductMoreFields) == MoreProductPage
+
+        # When there's no rule specifying to return this FakeItem
+        assert method(url, FakeItem) is None
+
+        # When the URL itself doesn't have any ``to_return`` in any of its rules
+        assert not method(cls("https://example.org"), FakeItem)
+
+
 def test_from_override_rules_deprecation_using_ApplyRule() -> None:
     rules = [
         ApplyRule(

web_poet/rules.py

@@ -347,6 +347,23 @@ def page_object_for(self, url: Union[_Url, str]) -> Mapping[Type, Type[ItemPage]
         """
         return self._rules_for_url(url, self._item_matchers)
 
+    def page_object_for_item(
+        self, url: Union[_Url, str], item_cls: Type
+    ) -> Optional[Type]:
+        """Return the page object class associated with the given URL that's able
+        to produce the given ``item_cls``.
+        """
+
+        url = str(url)
+
+        matcher = self._item_matchers.get(item_cls)
+        if matcher:
+            rule_id = matcher.match(url)
+            if rule_id is not None:
+                return self._rules[rule_id].use
+
+        return None
+
 
 def _walk_module(module: str) -> Iterable:
     """Return all modules from a module recursively.