core[performance]: use custom __getattr__ in __init__.py files for lazy imports (#30769)

Most easily reviewed with the "hide whitespace" option toggled.

Seeing 10-50% speed ups in import time for common structures 🚀 

The general purpose of this PR is to lazily import structures within
`langchain_core.XXX_module.__init__.py` so that we're not eagerly
importing expensive dependencies (`pydantic`, `requests`, etc).

Analysis of flamegraphs generated with `importtime` motivated these
changes. For example, the one below demonstrates that importing
`HumanMessage` accidentally triggered imports for `importlib.metadata`,
`requests`, etc.

There's still much more to do on this front, and we can start digging
into our own internal code for optimizations now that we're less
concerned about external imports.

<img width="1210" alt="Screenshot 2025-04-11 at 1 10 54 PM"
src="https://github.com/user-attachments/assets/112a3fe7-24a9-4294-92c1-d5ae64df839e"
/>

I've tracked the improvements with some local benchmarks:

## `pytest-benchmark` results

| Name | Before (s) | After (s) | Delta (s) | % Change |

|-----------------------------|------------|-----------|-----------|----------|
| Document | 2.8683 | 1.2775 | -1.5908 | -55.46% |
| HumanMessage | 2.2358 | 1.1673 | -1.0685 | -47.79% |
| ChatPromptTemplate | 5.5235 | 2.9709 | -2.5526 | -46.22% |
| Runnable | 2.9423 | 1.7793 | -1.163 | -39.53% |
| InMemoryVectorStore | 3.1180 | 1.8417 | -1.2763 | -40.93% |
| RunnableLambda | 2.7385 | 1.8745 | -0.864 | -31.55% |
| tool | 5.1231 | 4.0771 | -1.046 | -20.42% |
| CallbackManager | 4.2263 | 3.4099 | -0.8164 | -19.32% |
| LangChainTracer | 3.8394 | 3.3101 | -0.5293 | -13.79% |
| BaseChatModel | 4.3317 | 3.8806 | -0.4511 | -10.41% |
| PydanticOutputParser | 3.2036 | 3.2995 | 0.0959 | 2.99% |
| InMemoryRateLimiter | 0.5311 | 0.5995 | 0.0684 | 12.88% |

Note the lack of change for `InMemoryRateLimiter` and
`PydanticOutputParser` is just random noise, I'm getting comparable
numbers locally.

## Local CodSpeed results

We're still working on configuring CodSpeed on CI. The local usage
produced similar results.

libs/core/langchain_core/_api/__init__.py

@@ -9,6 +9,10 @@ This module is only relevant for LangChain developers, not for users.
 
 """
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
     from .beta_decorator import (
         LangChainBetaWarning,
         beta,
@@ -37,3 +41,33 @@ __all__ = [
     "surface_langchain_deprecation_warnings",
     "warn_deprecated",
 ]
+
+_dynamic_imports = {
+    "LangChainBetaWarning": "beta_decorator",
+    "beta": "beta_decorator",
+    "suppress_langchain_beta_warning": "beta_decorator",
+    "surface_langchain_beta_warnings": "beta_decorator",
+    "as_import_path": "path",
+    "get_relative_path": "path",
+    "LangChainDeprecationWarning": "deprecation",
+    "deprecated": "deprecation",
+    "surface_langchain_deprecation_warnings": "deprecation",
+    "suppress_langchain_deprecation_warning": "deprecation",
+    "warn_deprecated": "deprecation",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/callbacks/__init__.py

@@ -7,6 +7,10 @@
     BaseCallbackHandler --> <name>CallbackHandler  # Example: AimCallbackHandler
 """
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
     from langchain_core.callbacks.base import (
         AsyncCallbackHandler,
         BaseCallbackHandler,
@@ -84,3 +88,56 @@ __all__ = [
     "UsageMetadataCallbackHandler",
     "get_usage_metadata_callback",
 ]
+
+_dynamic_imports = {
+    "AsyncCallbackHandler": "base",
+    "BaseCallbackHandler": "base",
+    "BaseCallbackManager": "base",
+    "CallbackManagerMixin": "base",
+    "Callbacks": "base",
+    "ChainManagerMixin": "base",
+    "LLMManagerMixin": "base",
+    "RetrieverManagerMixin": "base",
+    "RunManagerMixin": "base",
+    "ToolManagerMixin": "base",
+    "FileCallbackHandler": "file",
+    "AsyncCallbackManager": "manager",
+    "AsyncCallbackManagerForChainGroup": "manager",
+    "AsyncCallbackManagerForChainRun": "manager",
+    "AsyncCallbackManagerForLLMRun": "manager",
+    "AsyncCallbackManagerForRetrieverRun": "manager",
+    "AsyncCallbackManagerForToolRun": "manager",
+    "AsyncParentRunManager": "manager",
+    "AsyncRunManager": "manager",
+    "BaseRunManager": "manager",
+    "CallbackManager": "manager",
+    "CallbackManagerForChainGroup": "manager",
+    "CallbackManagerForChainRun": "manager",
+    "CallbackManagerForLLMRun": "manager",
+    "CallbackManagerForRetrieverRun": "manager",
+    "CallbackManagerForToolRun": "manager",
+    "ParentRunManager": "manager",
+    "RunManager": "manager",
+    "adispatch_custom_event": "manager",
+    "dispatch_custom_event": "manager",
+    "StdOutCallbackHandler": "stdout",
+    "StreamingStdOutCallbackHandler": "streaming_stdout",
+    "UsageMetadataCallbackHandler": "usage",
+    "get_usage_metadata_callback": "usage",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/document_loaders/__init__.py

@@ -1,5 +1,9 @@
 """Document loaders."""
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
     from langchain_core.document_loaders.base import BaseBlobParser, BaseLoader
     from langchain_core.document_loaders.blob_loaders import Blob, BlobLoader, PathLike
     from langchain_core.document_loaders.langsmith import LangSmithLoader
@@ -12,3 +16,28 @@ __all__ = [
     "PathLike",
     "LangSmithLoader",
 ]
+
+_dynamic_imports = {
+    "BaseBlobParser": "base",
+    "BaseLoader": "base",
+    "Blob": "blob_loaders",
+    "BlobLoader": "blob_loaders",
+    "PathLike": "blob_loaders",
+    "LangSmithLoader": "langsmith",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/documents/__init__.py

@@ -5,8 +5,34 @@ and their transformations.
 
 """
 
-from langchain_core.documents.base import Document
-from langchain_core.documents.compressor import BaseDocumentCompressor
-from langchain_core.documents.transformers import BaseDocumentTransformer
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from .base import Document
+    from .compressor import BaseDocumentCompressor
+    from .transformers import BaseDocumentTransformer
 
 __all__ = ["Document", "BaseDocumentTransformer", "BaseDocumentCompressor"]
+
+_dynamic_imports = {
+    "Document": "base",
+    "BaseDocumentCompressor": "compressor",
+    "BaseDocumentTransformer": "transformers",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/embeddings/__init__.py

@@ -1,6 +1,35 @@
 """Embeddings."""
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
     from langchain_core.embeddings.embeddings import Embeddings
-from langchain_core.embeddings.fake import DeterministicFakeEmbedding, FakeEmbeddings
+    from langchain_core.embeddings.fake import (
+        DeterministicFakeEmbedding,
+        FakeEmbeddings,
+    )
 
 __all__ = ["DeterministicFakeEmbedding", "Embeddings", "FakeEmbeddings"]
+
+_dynamic_imports = {
+    "Embeddings": "embeddings",
+    "DeterministicFakeEmbedding": "fake",
+    "FakeEmbeddings": "fake",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/example_selectors/__init__.py

@@ -4,6 +4,10 @@
 This allows us to select examples that are most relevant to the input.
 """
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
     from langchain_core.example_selectors.base import BaseExampleSelector
     from langchain_core.example_selectors.length_based import (
         LengthBasedExampleSelector,
@@ -21,3 +25,27 @@ __all__ = [
     "SemanticSimilarityExampleSelector",
     "sorted_values",
 ]
+
+_dynamic_imports = {
+    "BaseExampleSelector": "base",
+    "LengthBasedExampleSelector": "length_based",
+    "MaxMarginalRelevanceExampleSelector": "semantic_similarity",
+    "SemanticSimilarityExampleSelector": "semantic_similarity",
+    "sorted_values": "semantic_similarity",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/indexing/__init__.py

@@ -5,6 +5,10 @@ a vectorstore while avoiding duplicated content and over-writing content
 if it's unchanged.
 """
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
     from langchain_core.indexing.api import IndexingResult, aindex, index
     from langchain_core.indexing.base import (
         DeleteResponse,
@@ -24,3 +28,30 @@ __all__ = [
     "RecordManager",
     "UpsertResponse",
 ]
+
+_dynamic_imports = {
+    "aindex": "api",
+    "index": "api",
+    "IndexingResult": "api",
+    "DeleteResponse": "base",
+    "DocumentIndex": "base",
+    "InMemoryRecordManager": "base",
+    "RecordManager": "base",
+    "UpsertResponse": "base",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/language_models/__init__.py

@@ -41,6 +41,10 @@ https://python.langchain.com/docs/how_to/custom_llm/
 
 """  # noqa: E501
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
     from langchain_core.language_models.base import (
         BaseLanguageModel,
         LangSmithParams,
@@ -49,7 +53,10 @@ from langchain_core.language_models.base import (
         LanguageModelOutput,
         get_tokenizer,
     )
-from langchain_core.language_models.chat_models import BaseChatModel, SimpleChatModel
+    from langchain_core.language_models.chat_models import (
+        BaseChatModel,
+        SimpleChatModel,
+    )
     from langchain_core.language_models.fake import FakeListLLM, FakeStreamingListLLM
     from langchain_core.language_models.fake_chat_models import (
         FakeListChatModel,
@@ -77,3 +84,38 @@ __all__ = [
     "GenericFakeChatModel",
     "ParrotFakeChatModel",
 ]
+
+_dynamic_imports = {
+    "BaseLanguageModel": "base",
+    "LangSmithParams": "base",
+    "LanguageModelInput": "base",
+    "LanguageModelLike": "base",
+    "LanguageModelOutput": "base",
+    "get_tokenizer": "base",
+    "BaseChatModel": "chat_models",
+    "SimpleChatModel": "chat_models",
+    "FakeListLLM": "fake",
+    "FakeStreamingListLLM": "fake",
+    "FakeListChatModel": "fake_chat_models",
+    "FakeMessagesListChatModel": "fake_chat_models",
+    "GenericFakeChatModel": "fake_chat_models",
+    "ParrotFakeChatModel": "fake_chat_models",
+    "LLM": "llms",
+    "BaseLLM": "llms",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/load/__init__.py

@@ -1,7 +1,35 @@
 """**Load** module helps with serialization and deserialization."""
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
     from langchain_core.load.dump import dumpd, dumps
     from langchain_core.load.load import load, loads
     from langchain_core.load.serializable import Serializable
 
 __all__ = ["dumpd", "dumps", "load", "loads", "Serializable"]
+
+_dynamic_imports = {
+    "dumpd": "dump",
+    "dumps": "dump",
+    "load": "load",
+    "loads": "load",
+    "Serializable": "serializable",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/messages/__init__.py

@@ -15,6 +15,10 @@
 
 """  # noqa: E501
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
     from langchain_core.messages.ai import (
         AIMessage,
         AIMessageChunk,
@@ -86,3 +90,54 @@ __all__ = [
     "trim_messages",
     "convert_to_openai_messages",
 ]
+
+_dynamic_imports = {
+    "AIMessage": "ai",
+    "AIMessageChunk": "ai",
+    "BaseMessage": "base",
+    "BaseMessageChunk": "base",
+    "merge_content": "base",
+    "message_to_dict": "base",
+    "messages_to_dict": "base",
+    "ChatMessage": "chat",
+    "ChatMessageChunk": "chat",
+    "FunctionMessage": "function",
+    "FunctionMessageChunk": "function",
+    "HumanMessage": "human",
+    "HumanMessageChunk": "human",
+    "RemoveMessage": "modifier",
+    "SystemMessage": "system",
+    "SystemMessageChunk": "system",
+    "InvalidToolCall": "tool",
+    "ToolCall": "tool",
+    "ToolCallChunk": "tool",
+    "ToolMessage": "tool",
+    "ToolMessageChunk": "tool",
+    "AnyMessage": "utils",
+    "MessageLikeRepresentation": "utils",
+    "_message_from_dict": "utils",
+    "convert_to_messages": "utils",
+    "convert_to_openai_messages": "utils",
+    "filter_messages": "utils",
+    "get_buffer_string": "utils",
+    "merge_message_runs": "utils",
+    "message_chunk_to_message": "utils",
+    "messages_from_dict": "utils",
+    "trim_messages": "utils",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/output_parsers/__init__.py

@@ -13,12 +13,19 @@
     Serializable, Generation, PromptValue
 """  # noqa: E501
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
     from langchain_core.output_parsers.base import (
         BaseGenerationOutputParser,
         BaseLLMOutputParser,
         BaseOutputParser,
     )
-from langchain_core.output_parsers.json import JsonOutputParser, SimpleJsonOutputParser
+    from langchain_core.output_parsers.json import (
+        JsonOutputParser,
+        SimpleJsonOutputParser,
+    )
     from langchain_core.output_parsers.list import (
         CommaSeparatedListOutputParser,
         ListOutputParser,
@@ -57,3 +64,39 @@ __all__ = [
     "JsonOutputKeyToolsParser",
     "PydanticToolsParser",
 ]
+
+_dynamic_imports = {
+    "BaseLLMOutputParser": "base",
+    "BaseGenerationOutputParser": "base",
+    "BaseOutputParser": "base",
+    "JsonOutputParser": "json",
+    "SimpleJsonOutputParser": "json",
+    "ListOutputParser": "list",
+    "CommaSeparatedListOutputParser": "list",
+    "MarkdownListOutputParser": "list",
+    "NumberedListOutputParser": "list",
+    "JsonOutputKeyToolsParser": "openai_tools",
+    "JsonOutputToolsParser": "openai_tools",
+    "PydanticToolsParser": "openai_tools",
+    "PydanticOutputParser": "pydantic",
+    "StrOutputParser": "string",
+    "BaseTransformOutputParser": "transform",
+    "BaseCumulativeTransformOutputParser": "transform",
+    "XMLOutputParser": "xml",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/outputs/__init__.py

@@ -21,7 +21,14 @@ in the AIMessage object, it is recommended to access it from there rather than
 from the `LLMResult` object.
 """
 
-from langchain_core.outputs.chat_generation import ChatGeneration, ChatGenerationChunk
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from langchain_core.outputs.chat_generation import (
+        ChatGeneration,
+        ChatGenerationChunk,
+    )
     from langchain_core.outputs.chat_result import ChatResult
     from langchain_core.outputs.generation import Generation, GenerationChunk
     from langchain_core.outputs.llm_result import LLMResult
@@ -36,3 +43,29 @@ __all__ = [
     "LLMResult",
     "RunInfo",
 ]
+
+_dynamic_imports = {
+    "ChatGeneration": "chat_generation",
+    "ChatGenerationChunk": "chat_generation",
+    "ChatResult": "chat_result",
+    "Generation": "generation",
+    "GenerationChunk": "generation",
+    "LLMResult": "llm_result",
+    "RunInfo": "run_info",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/prompts/__init__.py

@@ -25,6 +25,10 @@ from multiple components and prompt values. Prompt classes and functions make co
 
 """  # noqa: E501
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
     from langchain_core.prompts.base import (
         BasePromptTemplate,
         aformat_document,
@@ -43,7 +47,9 @@ from langchain_core.prompts.few_shot import (
         FewShotChatMessagePromptTemplate,
         FewShotPromptTemplate,
     )
-from langchain_core.prompts.few_shot_with_templates import FewShotPromptWithTemplates
+    from langchain_core.prompts.few_shot_with_templates import (
+        FewShotPromptWithTemplates,
+    )
     from langchain_core.prompts.loading import load_prompt
     from langchain_core.prompts.pipeline import PipelinePromptTemplate
     from langchain_core.prompts.prompt import PromptTemplate
@@ -78,3 +84,43 @@ __all__ = [
     "jinja2_formatter",
     "validate_jinja2",
 ]
+
+_dynamic_imports = {
+    "BasePromptTemplate": "base",
+    "format_document": "base",
+    "aformat_document": "base",
+    "AIMessagePromptTemplate": "chat",
+    "BaseChatPromptTemplate": "chat",
+    "ChatMessagePromptTemplate": "chat",
+    "ChatPromptTemplate": "chat",
+    "HumanMessagePromptTemplate": "chat",
+    "MessagesPlaceholder": "chat",
+    "SystemMessagePromptTemplate": "chat",
+    "FewShotChatMessagePromptTemplate": "few_shot",
+    "FewShotPromptTemplate": "few_shot",
+    "FewShotPromptWithTemplates": "few_shot_with_templates",
+    "load_prompt": "loading",
+    "PipelinePromptTemplate": "pipeline",
+    "PromptTemplate": "prompt",
+    "StringPromptTemplate": "string",
+    "check_valid_template": "string",
+    "get_template_variables": "string",
+    "jinja2_formatter": "string",
+    "validate_jinja2": "string",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/runnables/__init__.py

@@ -17,6 +17,10 @@ creating more responsive UX.
 This module contains schema and implementation of LangChain Runnables primitives.
 """
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
     from langchain_core.runnables.base import (
         Runnable,
         RunnableBinding,
@@ -85,3 +89,51 @@ __all__ = [
     "aadd",
     "add",
 ]
+
+_dynamic_imports = {
+    "chain": "base",
+    "Runnable": "base",
+    "RunnableBinding": "base",
+    "RunnableGenerator": "base",
+    "RunnableLambda": "base",
+    "RunnableMap": "base",
+    "RunnableParallel": "base",
+    "RunnableSequence": "base",
+    "RunnableSerializable": "base",
+    "RunnableBranch": "branch",
+    "RunnableConfig": "config",
+    "ensure_config": "config",
+    "get_config_list": "config",
+    "patch_config": "config",
+    "run_in_executor": "config",
+    "RunnableWithFallbacks": "fallbacks",
+    "RunnableWithMessageHistory": "history",
+    "RunnableAssign": "passthrough",
+    "RunnablePassthrough": "passthrough",
+    "RunnablePick": "passthrough",
+    "RouterInput": "router",
+    "RouterRunnable": "router",
+    "AddableDict": "utils",
+    "ConfigurableField": "utils",
+    "ConfigurableFieldMultiOption": "utils",
+    "ConfigurableFieldSingleOption": "utils",
+    "ConfigurableFieldSpec": "utils",
+    "aadd": "utils",
+    "add": "utils",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/tools/__init__.py

@@ -19,6 +19,10 @@ tool for the job.
 
 from __future__ import annotations
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
     from langchain_core.tools.base import (
         FILTERED_ARGS,
         ArgsSchema,
@@ -68,3 +72,41 @@ __all__ = [
     "Tool",
     "StructuredTool",
 ]
+
+_dynamic_imports = {
+    "FILTERED_ARGS": "base",
+    "ArgsSchema": "base",
+    "BaseTool": "base",
+    "BaseToolkit": "base",
+    "InjectedToolArg": "base",
+    "InjectedToolCallId": "base",
+    "SchemaAnnotationError": "base",
+    "ToolException": "base",
+    "_get_runnable_config_param": "base",
+    "create_schema_from_function": "base",
+    "convert_runnable_to_tool": "convert",
+    "tool": "convert",
+    "ToolsRenderer": "render",
+    "render_text_description": "render",
+    "render_text_description_and_args": "render",
+    "RetrieverInput": "retriever",
+    "create_retriever_tool": "retriever",
+    "Tool": "simple",
+    "StructuredTool": "structured",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/tracers/__init__.py

@@ -8,6 +8,21 @@
                                        --> <name>  # Examples: LogStreamCallbackHandler
 """  # noqa: E501
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from langchain_core.tracers.base import BaseTracer
+    from langchain_core.tracers.evaluation import EvaluatorCallbackHandler
+    from langchain_core.tracers.langchain import LangChainTracer
+    from langchain_core.tracers.log_stream import (
+        LogStreamCallbackHandler,
+        RunLog,
+        RunLogPatch,
+    )
+    from langchain_core.tracers.schemas import Run
+    from langchain_core.tracers.stdout import ConsoleCallbackHandler
+
 __all__ = [
     "BaseTracer",
     "EvaluatorCallbackHandler",
@@ -19,13 +34,29 @@ __all__ = [
     "LogStreamCallbackHandler",
 ]
 
-from langchain_core.tracers.base import BaseTracer
-from langchain_core.tracers.evaluation import EvaluatorCallbackHandler
-from langchain_core.tracers.langchain import LangChainTracer
-from langchain_core.tracers.log_stream import (
-    LogStreamCallbackHandler,
-    RunLog,
-    RunLogPatch,
-)
-from langchain_core.tracers.schemas import Run
-from langchain_core.tracers.stdout import ConsoleCallbackHandler
+_dynamic_imports = {
+    "BaseTracer": "base",
+    "EvaluatorCallbackHandler": "evaluation",
+    "LangChainTracer": "langchain",
+    "LogStreamCallbackHandler": "log_stream",
+    "RunLog": "log_stream",
+    "RunLogPatch": "log_stream",
+    "Run": "schemas",
+    "ConsoleCallbackHandler": "stdout",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)

libs/core/langchain_core/utils/__init__.py

@@ -3,6 +3,12 @@
 These functions do not depend on any other LangChain module.
 """
 
+from importlib import import_module
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    # for type checking and IDE support, we include the imports here
+    # but we don't want to eagerly import them at runtime
     from langchain_core.utils import image
     from langchain_core.utils.aiter import abatch_iterate
     from langchain_core.utils.env import get_from_dict_or_env, get_from_env
@@ -58,3 +64,48 @@ __all__ = [
     "from_env",
     "secret_from_env",
 ]
+
+_dynamic_imports = {
+    "image": "__module__",
+    "abatch_iterate": "aiter",
+    "get_from_dict_or_env": "env",
+    "get_from_env": "env",
+    "StrictFormatter": "formatting",
+    "formatter": "formatting",
+    "get_bolded_text": "input",
+    "get_color_mapping": "input",
+    "get_colored_text": "input",
+    "print_text": "input",
+    "batch_iterate": "iter",
+    "try_load_from_hub": "loading",
+    "pre_init": "pydantic",
+    "comma_list": "strings",
+    "stringify_dict": "strings",
+    "stringify_value": "strings",
+    "build_extra_kwargs": "utils",
+    "check_package_version": "utils",
+    "convert_to_secret_str": "utils",
+    "from_env": "utils",
+    "get_pydantic_field_names": "utils",
+    "guard_import": "utils",
+    "mock_now": "utils",
+    "secret_from_env": "utils",
+    "xor_args": "utils",
+    "raise_for_status_with_text": "utils",
+}
+
+
+def __getattr__(attr_name: str) -> object:
+    module_name = _dynamic_imports.get(attr_name)
+    package = __spec__.parent  # type: ignore[name-defined]
+    if module_name == "__module__" or module_name is None:
+        result = import_module(f".{attr_name}", package=package)
+    else:
+        module = import_module(f".{module_name}", package=package)
+        result = getattr(module, attr_name)
+    globals()[attr_name] = result
+    return result
+
+
+def __dir__() -> list[str]:
+    return list(__all__)