Implement better reprs for Runnables (#11175)

```
ChatPromptTemplate(messages=[SystemMessagePromptTemplate(prompt=PromptTemplate(input_variables=[], template='You are a nice assistant.')), HumanMessagePromptTemplate(prompt=PromptTemplate(input_variables=['question'], template='{question}'))])
| RunnableLambda(lambda x: x)
| {
    chat: FakeListChatModel(responses=["i'm a chatbot"]),
    llm: FakeListLLM(responses=["i'm a textbot"])
  }
```

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libs/langchain/langchain/load/serializable.py

@@ -77,6 +77,13 @@ class Serializable(BaseModel, ABC):
     class Config:
         extra = "ignore"
 
+    def __repr_args__(self) -> Any:
+        return [
+            (k, v)
+            for k, v in super().__repr_args__()
+            if (k not in self.__fields__ or self.__fields__[k].get_default() != v)
+        ]
+
     _lc_kwargs = PrivateAttr(default_factory=dict)
 
     def __init__(self, **kwargs: Any) -> None:

libs/langchain/langchain/schema/runnable/base.py

@@ -59,6 +59,8 @@ from langchain.schema.runnable.utils import (
     accepts_run_manager,
     gather_with_concurrency,
     get_function_first_arg_dict_keys,
+    get_lambda_source,
+    indent_lines_after_first,
 )
 from langchain.utils.aiter import atee, py_anext
 from langchain.utils.iter import safetee
@@ -1298,6 +1300,12 @@ class RunnableSequence(Serializable, Runnable[Input, Output]):
     def output_schema(self) -> Type[BaseModel]:
         return self.last.output_schema
 
+    def __repr__(self) -> str:
+        return "\n| ".join(
+            repr(s) if i == 0 else indent_lines_after_first(repr(s), "| ")
+            for i, s in enumerate(self.steps)
+        )
+
     def __or__(
         self,
         other: Union[
@@ -1819,6 +1827,13 @@ class RunnableMap(Serializable, Runnable[Input, Dict[str, Any]]):
             **{k: (v.OutputType, None) for k, v in self.steps.items()},
         )
 
+    def __repr__(self) -> str:
+        map_for_repr = ",\n  ".join(
+            f"{k}: {indent_lines_after_first(repr(v), '  ' + k + ': ')}"
+            for k, v in self.steps.items()
+        )
+        return "{\n  " + map_for_repr + "\n}"
+
     def invoke(
         self, input: Input, config: Optional[RunnableConfig] = None
     ) -> Dict[str, Any]:
@@ -2134,7 +2149,7 @@ class RunnableLambda(Runnable[Input, Output]):
             return False
 
     def __repr__(self) -> str:
-        return "RunnableLambda(...)"
+        return f"RunnableLambda({get_lambda_source(self.func) or '...'})"
 
     def _invoke(
         self,

libs/langchain/langchain/schema/runnable/utils.py

@@ -87,6 +87,17 @@ class IsFunctionArgDict(ast.NodeVisitor):
         IsLocalDict(input_arg_name, self.keys).visit(node)
 
 
+class GetLambdaSource(ast.NodeVisitor):
+    def __init__(self) -> None:
+        self.source: Optional[str] = None
+        self.count = 0
+
+    def visit_Lambda(self, node: ast.Lambda) -> Any:
+        self.count += 1
+        if hasattr(ast, "unparse"):
+            self.source = ast.unparse(node)
+
+
 def get_function_first_arg_dict_keys(func: Callable) -> Optional[List[str]]:
     try:
         code = inspect.getsource(func)
@@ -94,5 +105,40 @@ def get_function_first_arg_dict_keys(func: Callable) -> Optional[List[str]]:
         visitor = IsFunctionArgDict()
         visitor.visit(tree)
         return list(visitor.keys) if visitor.keys else None
-    except (TypeError, OSError):
+    except (SyntaxError, TypeError, OSError):
+        return None
+
+
+def get_lambda_source(func: Callable) -> Optional[str]:
+    """Get the source code of a lambda function.
+
+    Args:
+        func: a callable that can be a lambda function
+
+    Returns:
+        str: the source code of the lambda function
+    """
+    try:
+        code = inspect.getsource(func)
+        tree = ast.parse(textwrap.dedent(code))
+        visitor = GetLambdaSource()
+        visitor.visit(tree)
+        return visitor.source if visitor.count == 1 else None
+    except (SyntaxError, TypeError, OSError):
         return None
+
+
+def indent_lines_after_first(text: str, prefix: str) -> str:
+    """Indent all lines of text after the first line.
+
+    Args:
+        text:  The text to indent
+        prefix: Used to determine the number of spaces to indent
+
+    Returns:
+        str: The indented text
+    """
+    n_spaces = len(prefix)
+    spaces = " " * n_spaces
+    lines = text.splitlines()
+    return "\n".join([lines[0]] + [spaces + line for line in lines[1:]])

libs/langchain/tests/unit_tests/schema/runnable/test_runnable.py

@@ -867,6 +867,7 @@ async def test_prompt_with_chat_model(
 
     chain = prompt | chat
 
+    assert repr(chain) == snapshot
     assert isinstance(chain, RunnableSequence)
     assert chain.first == prompt
     assert chain.middle == []
@@ -1276,7 +1277,8 @@ def test_combining_sequences(
     assert chain.first == prompt
     assert chain.middle == [chat]
     assert chain.last == parser
-    assert dumps(chain, pretty=True) == snapshot
+    if sys.version_info >= (3, 9):
+        assert dumps(chain, pretty=True) == snapshot
 
     prompt2 = (
         SystemMessagePromptTemplate.from_template("You are a nicer assistant.")
@@ -1294,7 +1296,8 @@ def test_combining_sequences(
     assert chain2.first == input_formatter
     assert chain2.middle == [prompt2, chat2]
     assert chain2.last == parser2
-    assert dumps(chain2, pretty=True) == snapshot
+    if sys.version_info >= (3, 9):
+        assert dumps(chain2, pretty=True) == snapshot
 
     combined_chain = chain | chain2
 
@@ -1307,7 +1310,8 @@ def test_combining_sequences(
         chat2,
     ]
     assert combined_chain.last == parser2
-    assert dumps(combined_chain, pretty=True) == snapshot
+    if sys.version_info >= (3, 9):
+        assert dumps(combined_chain, pretty=True) == snapshot
 
     # Test invoke
     tracer = FakeTracer()
@@ -1315,7 +1319,8 @@ def test_combining_sequences(
         {"question": "What is your name?"}, dict(callbacks=[tracer])
     ) == ["baz", "qux"]
 
-    assert tracer.runs == snapshot
+    if sys.version_info >= (3, 9):
+        assert tracer.runs == snapshot
 
 
 @freeze_time("2023-01-01")
@@ -1350,6 +1355,7 @@ Question:
         | parser
     )
 
+    assert repr(chain) == snapshot
     assert isinstance(chain, RunnableSequence)
     assert isinstance(chain.first, RunnableMap)
     assert chain.middle == [prompt, chat]
@@ -1375,7 +1381,7 @@ Question:
             SystemMessage(content="You are a nice assistant."),
             HumanMessage(
                 content="""Context:
-[Document(page_content='foo', metadata={}), Document(page_content='bar', metadata={})]
+[Document(page_content='foo'), Document(page_content='bar')]
 
 Question:
 What is your name?"""
@@ -1413,6 +1419,7 @@ def test_seq_prompt_dict(mocker: MockerFixture, snapshot: SnapshotAssertion) ->
         }
     )
 
+    assert repr(chain) == snapshot
     assert isinstance(chain, RunnableSequence)
     assert chain.first == prompt
     assert chain.middle == [RunnableLambda(passthrough)]
@@ -2098,7 +2105,8 @@ async def test_llm_with_fallbacks(
     assert await runnable.ainvoke("hello") == "bar"
     assert await runnable.abatch(["hi", "hey", "bye"]) == ["bar"] * 3
     assert list(await runnable.ainvoke("hello")) == list("bar")
-    assert dumps(runnable, pretty=True) == snapshot
+    if sys.version_info >= (3, 9):
+        assert dumps(runnable, pretty=True) == snapshot
 
 
 class FakeSplitIntoListParser(BaseOutputParser[List[str]]):
@@ -2196,6 +2204,7 @@ def test_retrying(mocker: MockerFixture) -> None:
     with pytest.raises(RuntimeError):
         runnable.with_retry(
             stop_after_attempt=2,
+            wait_exponential_jitter=False,
             retry_if_exception_type=(ValueError,),
         ).invoke(2)
 
@@ -2205,6 +2214,7 @@ def test_retrying(mocker: MockerFixture) -> None:
     with pytest.raises(ValueError):
         runnable.with_retry(
             stop_after_attempt=2,
+            wait_exponential_jitter=False,
             retry_if_exception_type=(ValueError,),
         ).batch([1, 2, 0])
 
@@ -2214,6 +2224,7 @@ def test_retrying(mocker: MockerFixture) -> None:
 
     output = runnable.with_retry(
         stop_after_attempt=2,
+        wait_exponential_jitter=False,
         retry_if_exception_type=(ValueError,),
     ).batch([1, 2, 0], return_exceptions=True)
 
@@ -2248,6 +2259,7 @@ async def test_async_retrying(mocker: MockerFixture) -> None:
     with pytest.raises(ValueError):
         await runnable.with_retry(
             stop_after_attempt=2,
+            wait_exponential_jitter=False,
             retry_if_exception_type=(ValueError, KeyError),
         ).ainvoke(1)
 
@@ -2257,6 +2269,7 @@ async def test_async_retrying(mocker: MockerFixture) -> None:
     with pytest.raises(RuntimeError):
         await runnable.with_retry(
             stop_after_attempt=2,
+            wait_exponential_jitter=False,
             retry_if_exception_type=(ValueError,),
         ).ainvoke(2)
 
@@ -2266,6 +2279,7 @@ async def test_async_retrying(mocker: MockerFixture) -> None:
     with pytest.raises(ValueError):
         await runnable.with_retry(
             stop_after_attempt=2,
+            wait_exponential_jitter=False,
             retry_if_exception_type=(ValueError,),
         ).abatch([1, 2, 0])
 
@@ -2275,6 +2289,7 @@ async def test_async_retrying(mocker: MockerFixture) -> None:
 
     output = await runnable.with_retry(
         stop_after_attempt=2,
+        wait_exponential_jitter=False,
         retry_if_exception_type=(ValueError,),
     ).abatch([1, 2, 0], return_exceptions=True)
 
@@ -2729,3 +2744,38 @@ async def test_runnable_branch_abatch() -> None:
     )
 
     assert await branch.abatch([1, 10, 0]) == [2, 100, -1]
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 9), reason="Requires python version >= 3.9 to run."
+)
+def test_representation_of_runnables() -> None:
+    """Test representation of runnables."""
+    runnable = RunnableLambda(lambda x: x * 2)
+    assert repr(runnable) == "RunnableLambda(lambda x: x * 2)"
+
+    def f(x: int) -> int:
+        """Return 2."""
+        return 2
+
+    assert repr(RunnableLambda(func=f)) == "RunnableLambda(...)"
+
+    async def af(x: int) -> int:
+        """Return 2."""
+        return 2
+
+    assert repr(RunnableLambda(func=f, afunc=af)) == "RunnableLambda(...)"
+
+    assert repr(
+        RunnableLambda(lambda x: x + 2)
+        | {
+            "a": RunnableLambda(lambda x: x * 2),
+            "b": RunnableLambda(lambda x: x * 3),
+        }
+    ) == (
+        "RunnableLambda(...)\n"
+        "| {\n"
+        "    a: RunnableLambda(...),\n"
+        "    b: RunnableLambda(...)\n"
+        "  }"
+    ), "repr where code string contains multiple lambdas gives up"

libs/langchain/tests/unit_tests/schema/runnable/test_utils.py

@@ -0,0 +1,39 @@
+import sys
+from typing import Callable
+
+import pytest
+
+from langchain.schema.runnable.utils import (
+    get_lambda_source,
+    indent_lines_after_first,
+)
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 9), reason="Requires python version >= 3.9 to run."
+)
+@pytest.mark.parametrize(
+    "func, expected_source",
+    [
+        (lambda x: x * 2, "lambda x: x * 2"),
+        (lambda a, b: a + b, "lambda a, b: a + b"),
+        (lambda x: x if x > 0 else 0, "lambda x: x if x > 0 else 0"),
+    ],
+)
+def test_get_lambda_source(func: Callable, expected_source: str) -> None:
+    """Test get_lambda_source function"""
+    source = get_lambda_source(func)
+    assert source == expected_source
+
+
+@pytest.mark.parametrize(
+    "text,prefix,expected_output",
+    [
+        ("line 1\nline 2\nline 3", "1", "line 1\n line 2\n line 3"),
+        ("line 1\nline 2\nline 3", "ax", "line 1\n  line 2\n  line 3"),
+    ],
+)
+def test_indent_lines_after_first(text: str, prefix: str, expected_output: str) -> None:
+    """Test indent_lines_after_first function"""
+    indented_text = indent_lines_after_first(text, prefix)
+    assert indented_text == expected_output