Harrison/single input (#347)

allow passing of single input into chain

Co-authored-by: thepok <richterthepok@yahoo.de>

langchain/chains/base.py

@@ -1,6 +1,6 @@
 """Base interface that all chains should implement."""
 from abc import ABC, abstractmethod
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, List, Optional, Union
 
 from pydantic import BaseModel, Extra, Field
 
@@ -74,18 +74,28 @@ class Chain(BaseModel, ABC):
         """Run the logic of this chain and return the output."""
 
     def __call__(
-        self, inputs: Dict[str, Any], return_only_outputs: bool = False
+        self, inputs: Union[Dict[str, Any], Any], return_only_outputs: bool = False
     ) -> Dict[str, str]:
         """Run the logic of this chain and add to output if desired.
 
         Args:
-            inputs: Dictionary of inputs.
+            inputs: Dictionary of inputs, or single input if chain expects
+                only one param.
             return_only_outputs: boolean for whether to return only outputs in the
                 response. If True, only new keys generated by this chain will be
                 returned. If False, both input keys and new keys generated by this
                 chain will be returned. Defaults to False.
 
         """
+        if not isinstance(inputs, dict):
+            if len(self.input_keys) != 1:
+                raise ValueError(
+                    f"A single string input was passed in, but this chain expects "
+                    f"multiple inputs ({self.input_keys}). When a chain expects "
+                    f"multiple inputs, please call it by passing in a dictionary, "
+                    "eg `chain({'foo': 1, 'bar': 2})`"
+                )
+            inputs = {self.input_keys[0]: inputs}
         if self.memory is not None:
             external_context = self.memory.load_memory_variables(inputs)
             inputs = dict(inputs, **external_context)

tests/unit_tests/chains/test_base.py

@@ -11,11 +11,12 @@ class FakeChain(Chain, BaseModel):
     """Fake chain class for testing purposes."""
 
     be_correct: bool = True
+    the_input_keys: List[str] = ["foo"]
 
     @property
     def input_keys(self) -> List[str]:
-        """Input key of foo."""
-        return ["foo"]
+        """Input keys."""
+        return self.the_input_keys
 
     @property
     def output_keys(self) -> List[str]:
@@ -48,3 +49,17 @@ def test_correct_call() -> None:
     chain = FakeChain()
     output = chain({"foo": "bar"})
     assert output == {"foo": "bar", "bar": "baz"}
+
+
+def test_single_input_correct() -> None:
+    """Test passing single input works."""
+    chain = FakeChain()
+    output = chain("bar")
+    assert output == {"foo": "bar", "bar": "baz"}
+
+
+def test_single_input_error() -> None:
+    """Test passing single input errors as expected."""
+    chain = FakeChain(the_input_keys=["foo", "bar"])
+    with pytest.raises(ValueError):
+        chain("bar")