Import a Space as a tool: Exception: Tool's 'forward' method should take 'self' as its first argument, ...

[didierguillevic]

Hi,

Going through the smolagents documentation :-) :-)

The Import a Space as a tool example is not running as expected.

Code:

image_generation_tool = Tool.from_space(
    "black-forest-labs/FLUX.1-schnell",
    name="image_generator",
    description="Generate an image from a prompt"
)

image_generation_tool("A sunny beach")

Output:

---------------------------------------------------------------------------
Exception                                 Traceback (most recent call last)
Cell In[28], [line 1](vscode-notebook-cell:?execution_count=28&line=1)
----> [1](vscode-notebook-cell:?execution_count=28&line=1) image_generation_tool = smolagents.Tool.from_space(
      [2](vscode-notebook-cell:?execution_count=28&line=2)     "black-forest-labs/FLUX.1-schnell",
      [3](vscode-notebook-cell:?execution_count=28&line=3)     name="image_generator",
      [4](vscode-notebook-cell:?execution_count=28&line=4)     description="Generate an image from a prompt"
      [5](vscode-notebook-cell:?execution_count=28&line=5) )
      [7](vscode-notebook-cell:?execution_count=28&line=7) image_generation_tool("A sunny beach")

File /opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:657, in Tool.from_space(space_id, name, description, api_name, token)
    [652](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:652)             return output[
    [653](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:653)                 0
    [654](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:654)             ]  # Sometime the space also returns the generation seed, in which case the result is at index 0
    [655](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:655)         return output
--> [657](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:657) return SpaceToolWrapper(
    [658](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:658)     space_id=space_id,
    [659](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:659)     name=name,
    [660](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:660)     description=description,
    [661](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:661)     api_name=api_name,
    [662](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:662)     token=token,
    [663](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:663) )

File /opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:107, in validate_after_init.<locals>.new_init(self, *args, **kwargs)
    [104](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:104) @wraps(original_init)
    [105](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:105) def new_init(self, *args, **kwargs):
    [106](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:106)     original_init(self, *args, **kwargs)
--> [107](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:107)     self.validate_arguments()

File /opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:217, in Tool.validate_arguments(self)
    [214](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:214) signature = inspect.signature(self.forward)
    [216](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:216) if not set(signature.parameters.keys()) == set(self.inputs.keys()):
--> [217](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:217)     raise Exception(
    [218](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:218)         "Tool's 'forward' method should take 'self' as its first argument, then its next arguments should match the keys of tool attribute 'inputs'."
    [219](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:219)     )
    [221](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:221) json_schema = _convert_type_hints_to_json_schema(self.forward)
    [222](https://file+.vscode-resource.vscode-cdn.net/opt/anaconda3/envs/smol/lib/python3.10/site-packages/smolagents/tools.py:222) for key, value in self.inputs.items():

Exception: Tool's 'forward' method should take 'self' as its first argument, then its next arguments should match the keys of tool attribute 'inputs'.

Environment:

• smolagents==1.0.0
• torch==2.5.1
• macOS 15.2 (M processor)

[lelayf]

Confirming the same issue with that specific example.

The root cause is that method SpaceToolWrapper.forward relies on *args and **kwargs in its signature:

def forward(self, *args, **kwargs):
    # Preprocess args and kwargs:
    args = list(args)
    for i, arg in enumerate(args):
        args[i] = self.sanitize_argument_for_prediction(arg)
    for arg_name, arg in kwargs.items():
        kwargs[arg_name] = self.sanitize_argument_for_prediction(arg)

    output = self.client.predict(*args, api_name=self.api_name, **kwargs)
    if isinstance(output, tuple) or isinstance(output, list):
        return output[
            0
        ]  # Sometime the space also returns the generation seed, in which case the result is at index 0
    return output

When it is instantiated, the call to validate_arguments raises an exception if the input spec retrieved from the space does not match the forward signature spec. In this case the forward signature is still very generic as a odict_keys(['args', 'kwargs']), and it does not match the expected space input params which come as a dict(['prompt']).

The PipelineTool has a similar situation and avoids the failure by having a is_pipeline_tool class variable that the validation checks against to bypass signature matching.

# Validate forward function signature, except for PipelineTool
if not (
    hasattr(self, "is_pipeline_tool")
    and getattr(self, "is_pipeline_tool") is True
):

I think we should:

• add a skip_forward_signature_validation class variable in the SpaceToolWrapper
• rename PipelineTool.is_pipeline_tool to PipelineTool.skip_forward_signature_validation
• modify the validate_arguments method to check skip_forward_signature_validation instead of is_pipeline_tool