Add auxiliary methods for KB (and InMemoryLookupKB).

spacy/kb/kb.pyx

@@ -1,7 +1,7 @@
 # cython: infer_types=True, profile=True
 
 from pathlib import Path
-from typing import Iterable, Tuple, Union
+from typing import Iterable, Tuple, Union, TypeVar, Type
 from cymem.cymem cimport Pool
 
 from .candidate import Candidate
@@ -18,6 +18,8 @@ cdef class KnowledgeBase:
     DOCS: https://spacy.io/api/kb
     """
 
+    _KBType = TypeVar("_KBType", bound=KnowledgeBase)
+
     def __init__(self, vocab: Vocab, entity_vector_length: int):
         """Create a KnowledgeBase."""
         # Make sure abstract KB is not instantiated.
@@ -106,3 +108,25 @@ cdef class KnowledgeBase:
         raise NotImplementedError(
             Errors.E1045.format(parent="KnowledgeBase", method="from_disk", name=self.__name__)
         )
+
+    @classmethod
+    def generate_from_disk(
+        cls: Type[_KBType], path: Union[str, Path], exclude: Iterable[str] = SimpleFrozenList()
+    ) -> _KBType:
+        """
+        Factory method for generating KnowledgeBase subclass instance from file.
+        path (Union[str, Path]): Target file path.
+        exclude (Iterable[str]): List of components to exclude.
+        return (_KBType): Instance of KnowledgeBase subclass generated from file.
+        """
+        raise NotImplementedError(
+            Errors.E1044.format(parent="KnowledgeBase", method="generate_from_disk", name=cls.__name__)
+        )
+
+    def __len__(self) -> int:
+        """Returns number of entities in the KnowledgeBase.
+        RETURNS (int): Number of entities in the KnowledgeBase.
+        """
+        raise NotImplementedError(
+            Errors.E1044.format(parent="KnowledgeBase", method="__len__", name=self.__name__)
+        )

spacy/kb/kb_in_memory.pyx

@@ -46,6 +46,14 @@ cdef class InMemoryLookupKB(KnowledgeBase):
         self._alias_index = PreshMap(nr_aliases + 1)
         self._aliases_table = alias_vec(nr_aliases + 1)
 
+    @classmethod
+    def generate_from_disk(
+        cls, path: Union[str, Path], exclude: Iterable[str] = SimpleFrozenList()
+    ) -> "InMemoryLookupKB":
+        kb = InMemoryLookupKB(vocab=Vocab(strings=["."]), entity_vector_length=1)
+        kb.from_disk(path)
+        return kb
+
     def __len__(self):
         return self.get_size_entities()