ci: Enable mypy checks for checkpoint lib

libs/checkpoint/Makefile

@@ -27,7 +27,8 @@ lint lint_diff lint_package lint_tests:
 	poetry run ruff check .
 	[ "$(PYTHON_FILES)" = "" ] || poetry run ruff format $(PYTHON_FILES) --diff
 	[ "$(PYTHON_FILES)" = "" ] || poetry run ruff check --select I $(PYTHON_FILES)
-	[ "$(PYTHON_FILES)" = "" ] || mkdir -p $(MYPY_CACHE) || poetry run mypy $(PYTHON_FILES) --cache-dir $(MYPY_CACHE)
+	[ "$(PYTHON_FILES)" = "" ] || mkdir -p $(MYPY_CACHE)
+	[ "$(PYTHON_FILES)" = "" ] || poetry run mypy $(PYTHON_FILES) --cache-dir $(MYPY_CACHE)
 
 format format_diff:
 	poetry run ruff format $(PYTHON_FILES)

libs/checkpoint/langgraph/checkpoint/base/__init__.py

@@ -3,6 +3,7 @@ from typing import (
     Any,
     AsyncIterator,
     Dict,
+    Generic,
     Iterator,
     List,
     Literal,
@@ -135,7 +136,7 @@ def create_checkpoint(
     if channels is None:
         values = checkpoint["channel_values"]
     else:
-        values: dict[str, Any] = {}
+        values = {}
         for k, v in channels.items():
             if k not in checkpoint["channel_versions"]:
                 continue
@@ -192,7 +193,7 @@ CheckpointId = ConfigurableFieldSpec(
 )
 
 
-class BaseCheckpointSaver:
+class BaseCheckpointSaver(Generic[V]):
     """Base class for creating a graph checkpointer.
 
     Checkpointers allow LangGraph agents to persist their state
@@ -420,7 +421,12 @@ class BaseCheckpointSaver:
         Returns:
             V: The next version identifier, which must be increasing.
         """
-        return current + 1 if current is not None else 1
+        if isinstance(current, str):
+            raise NotImplementedError
+        elif current is None:
+            return 1  # type: ignore[return-value]
+        else:
+            return current + 1
 
 
 class EmptyChannelError(Exception):

libs/checkpoint/langgraph/checkpoint/memory/__init__.py

@@ -22,7 +22,7 @@ from langgraph.checkpoint.serde.types import TASKS, ChannelProtocol
 
 
 class MemorySaver(
-    BaseCheckpointSaver, AbstractContextManager, AbstractAsyncContextManager
+    BaseCheckpointSaver[str], AbstractContextManager, AbstractAsyncContextManager
 ):
     """An in-memory checkpoint saver.
 
@@ -54,9 +54,14 @@ class MemorySaver(
     """
 
     # thread ID ->  checkpoint NS -> checkpoint ID -> checkpoint mapping
-    storage: defaultdict[str, dict[str, dict[str, tuple[bytes, bytes, Optional[str]]]]]
+    storage: defaultdict[
+        str,
+        dict[
+            str, dict[str, tuple[tuple[str, bytes], tuple[str, bytes], Optional[str]]]
+        ],
+    ]
     writes: defaultdict[
-        tuple[str, str, str], dict[tuple[str, int], tuple[str, str, bytes]]
+        tuple[str, str, str], dict[tuple[str, int], tuple[str, str, tuple[str, bytes]]]
     ]
 
     def __init__(
@@ -316,7 +321,7 @@ class MemorySaver(
             RunnableConfig: The updated config containing the saved checkpoint's timestamp.
         """
         c = checkpoint.copy()
-        c.pop("pending_sends")
+        c.pop("pending_sends")  # type: ignore[misc]
         thread_id = config["configurable"]["thread_id"]
         checkpoint_ns = config["configurable"]["checkpoint_ns"]
         self.storage[thread_id][checkpoint_ns].update(
@@ -341,7 +346,7 @@ class MemorySaver(
         config: RunnableConfig,
         writes: List[Tuple[str, Any]],
         task_id: str,
-    ) -> RunnableConfig:
+    ) -> None:
         """Save a list of writes to the in-memory storage.
 
         This method saves a list of writes to the in-memory storage. The writes are associated
@@ -444,7 +449,7 @@ class MemorySaver(
         config: RunnableConfig,
         writes: List[Tuple[str, Any]],
         task_id: str,
-    ) -> RunnableConfig:
+    ) -> None:
         """Asynchronous version of put_writes.
 
         This method is an asynchronous wrapper around put_writes that runs the synchronous

libs/checkpoint/langgraph/checkpoint/serde/base.py

@@ -25,6 +25,12 @@ class SerializerCompat(SerializerProtocol):
     def __init__(self, serde: SerializerProtocol) -> None:
         self.serde = serde
 
+    def dumps(self, obj: Any) -> bytes:
+        return self.serde.dumps(obj)
+
+    def loads(self, data: bytes) -> Any:
+        return self.serde.loads(data)
+
     def dumps_typed(self, obj: Any) -> tuple[str, bytes]:
         return type(obj).__name__, self.serde.dumps(obj)
 

libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py

@@ -16,10 +16,10 @@ from ipaddress import (
     IPv6Interface,
     IPv6Network,
 )
-from typing import Any, Optional, Sequence
+from typing import Any, Callable, Optional, Sequence, Union, cast
 from uuid import UUID
 
-import msgpack
+import msgpack  # type: ignore[import-untyped]
 from langchain_core.load.load import Reviver
 from langchain_core.load.serializable import Serializable
 from zoneinfo import ZoneInfo
@@ -33,12 +33,12 @@ LC_REVIVER = Reviver()
 class JsonPlusSerializer(SerializerProtocol):
     def _encode_constructor_args(
         self,
-        constructor: type[Any],
+        constructor: Union[Callable, type[Any]],
         *,
-        method: Optional[str] = None,
+        method: Union[None, str, Sequence[Union[None, str]]] = None,
         args: Optional[Sequence[Any]] = None,
         kwargs: Optional[dict[str, Any]] = None,
-    ):
+    ) -> dict[str, Any]:
         out = {
             "lc": 2,
             "type": "constructor",
@@ -52,9 +52,9 @@ class JsonPlusSerializer(SerializerProtocol):
             out["kwargs"] = kwargs
         return out
 
-    def _default(self, obj):
+    def _default(self, obj: Any) -> Union[str, dict[str, Any]]:
         if isinstance(obj, Serializable):
-            return obj.to_json()
+            return cast(dict[str, Any], obj.to_json())
         elif hasattr(obj, "model_dump") and callable(obj.model_dump):
             return self._encode_constructor_args(
                 obj.__class__, method=(None, "model_construct"), kwargs=obj.model_dump()
@@ -87,7 +87,10 @@ class JsonPlusSerializer(SerializerProtocol):
                 datetime, method="fromisoformat", args=(obj.isoformat(),)
             )
         elif isinstance(obj, timezone):
-            return self._encode_constructor_args(timezone, args=obj.__getinitargs__())
+            return self._encode_constructor_args(
+                timezone,
+                args=obj.__getinitargs__(),  # type: ignore[attr-defined]
+            )
         elif isinstance(obj, ZoneInfo):
             return self._encode_constructor_args(ZoneInfo, args=(obj.key,))
         elif isinstance(obj, timedelta):
@@ -217,7 +220,7 @@ EXT_PYDANTIC_V1 = 4
 EXT_PYDANTIC_V2 = 5
 
 
-def _msgpack_default(obj):
+def _msgpack_default(obj: Any) -> Union[str, msgpack.ExtType]:
     if hasattr(obj, "model_dump") and callable(obj.model_dump):  # pydantic v2
         return msgpack.ExtType(
             EXT_PYDANTIC_V2,
@@ -360,7 +363,7 @@ def _msgpack_default(obj):
                 (
                     obj.__class__.__module__,
                     obj.__class__.__name__,
-                    obj.__getinitargs__(),
+                    obj.__getinitargs__(),  # type: ignore[attr-defined]
                 ),
             ),
         )
@@ -406,7 +409,7 @@ def _msgpack_default(obj):
         raise TypeError(f"Object of type {obj.__class__.__name__} is not serializable")
 
 
-def _msgpack_ext_hook(code: int, data: bytes):
+def _msgpack_ext_hook(code: int, data: bytes) -> Any:
     if code == EXT_CONSTRUCTOR_SINGLE_ARG:
         try:
             tup = msgpack.unpackb(data, ext_hook=_msgpack_ext_hook)
@@ -461,7 +464,7 @@ def _msgpack_ext_hook(code: int, data: bytes):
             return
 
 
-ENC_POOL = deque(maxlen=32)
+ENC_POOL: deque[msgpack.Packer] = deque(maxlen=32)
 
 
 def _msgpack_enc(data: Any) -> bytes:

libs/checkpoint/langgraph/checkpoint/serde/types.py

@@ -16,8 +16,8 @@ ERROR = "__error__"
 SCHEDULED = "__scheduled__"
 TASKS = "__pregel_tasks"
 
-Value = TypeVar("Value")
-Update = TypeVar("Update")
+Value = TypeVar("Value", covariant=True)
+Update = TypeVar("Update", contravariant=True)
 C = TypeVar("C")
 
 

libs/checkpoint/pyproject.toml

@@ -53,3 +53,13 @@ now = true
 delay = 0.1
 runner_args = ["--ff", "-v", "--tb", "short"]
 patterns = ["*.py"]
+
+[tool.mypy]
+# https://mypy.readthedocs.io/en/stable/config_file.html
+disallow_untyped_defs = "True"
+explicit_package_bases = "True"
+warn_no_return = "False"
+warn_unused_ignores = "True"
+warn_redundant_casts = "True"
+allow_redefinition = "True"
+disable_error_code = "typeddict-item, return-value"