change run to use args and kwargs (#367)

Before, `run` was not able to be called with multiple arguments. This
expands the functionality.

.flake8

@@ -1,5 +1,6 @@
 [flake8]
 exclude =
+    venv
     .venv
     __pycache__
     notebooks

langchain/chains/base.py

@@ -119,16 +119,23 @@ class Chain(BaseModel, ABC):
         """Call the chain on all inputs in the list."""
         return [self(inputs) for inputs in input_list]
 
-    def run(self, text: str) -> str:
-        """Run text in, text out (if applicable)."""
-        if len(self.input_keys) != 1:
-            raise ValueError(
-                f"`run` not supported when there is not exactly "
-                f"one input key, got {self.input_keys}."
-            )
+    def run(self, *args: str, **kwargs: str) -> str:
+        """Run the chain as text in, text out or multiple variables, text out."""
         if len(self.output_keys) != 1:
             raise ValueError(
                 f"`run` not supported when there is not exactly "
-                f"one output key, got {self.output_keys}."
+                f"one output key. Got {self.output_keys}."
             )
-        return self({self.input_keys[0]: text})[self.output_keys[0]]
+
+        if args and not kwargs:
+            if len(args) != 1:
+                raise ValueError("`run` supports only one positional argument.")
+            return self(args[0])[self.output_keys[0]]
+
+        if kwargs and not args:
+            return self(kwargs)[self.output_keys[0]]
+
+        raise ValueError(
+            f"`run` supported with either positional arguments or keyword arguments"
+            f" but not both. Got args: {args} and kwargs: {kwargs}."
+        )

tests/unit_tests/chains/test_base.py

@@ -12,6 +12,7 @@ class FakeChain(Chain, BaseModel):
 
     be_correct: bool = True
     the_input_keys: List[str] = ["foo"]
+    the_output_keys: List[str] = ["bar"]
 
     @property
     def input_keys(self) -> List[str]:
@@ -21,7 +22,7 @@ class FakeChain(Chain, BaseModel):
     @property
     def output_keys(self) -> List[str]:
         """Output key of bar."""
-        return ["bar"]
+        return self.the_output_keys
 
     def _call(self, inputs: Dict[str, str]) -> Dict[str, str]:
         if self.be_correct:
@@ -63,3 +64,45 @@ def test_single_input_error() -> None:
     chain = FakeChain(the_input_keys=["foo", "bar"])
     with pytest.raises(ValueError):
         chain("bar")
+
+
+def test_run_single_arg() -> None:
+    """Test run method with single arg."""
+    chain = FakeChain()
+    output = chain.run("bar")
+    assert output == "baz"
+
+
+def test_run_multiple_args_error() -> None:
+    """Test run method with multiple args errors as expected."""
+    chain = FakeChain()
+    with pytest.raises(ValueError):
+        chain.run("bar", "foo")
+
+
+def test_run_kwargs() -> None:
+    """Test run method with kwargs."""
+    chain = FakeChain(the_input_keys=["foo", "bar"])
+    output = chain.run(foo="bar", bar="foo")
+    assert output == "baz"
+
+
+def test_run_kwargs_error() -> None:
+    """Test run method with kwargs errors as expected."""
+    chain = FakeChain(the_input_keys=["foo", "bar"])
+    with pytest.raises(ValueError):
+        chain.run(foo="bar", baz="foo")
+
+
+def test_run_args_and_kwargs_error() -> None:
+    """Test run method with args and kwargs."""
+    chain = FakeChain(the_input_keys=["foo", "bar"])
+    with pytest.raises(ValueError):
+        chain.run("bar", foo="bar")
+
+
+def test_multiple_output_keys_error() -> None:
+    """Test run with multiple output keys errors as expected."""
+    chain = FakeChain(the_output_keys=["foo", "bar"])
+    with pytest.raises(ValueError):
+        chain.run("bar")