Issues that occur when loading custom components (circular import)

[KSH94]

I am unable to load the custom component.
I was following the guide in https://docs.langflow.org/tutorials/custom_components .

Below is what I did:

1. Create the /workspace/custom_components directory
2. Create a Python script (custon component class) shown in the guide under the above directory.
3. Run langflow using the --components-path option as shown below.

langflow run --components-path /workspace/custom_components

However, I could not find the custom component menu in the sidebar of the displayed langflow UI.

While looking for the cause, I found that an error occurred in the import statement below.

from langflow.custom import CustomComponent

The error details are as follows.

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.10/site-packages/langflow/custom/__init__.py", line 1, in <module>
    from langflow.custom.custom_component import CustomComponent
  File "/usr/local/lib/python3.10/site-packages/langflow/custom/custom_component/__init__.py", line 1, in <module>
    from .custom_component import CustomComponent
  File "/usr/local/lib/python3.10/site-packages/langflow/custom/custom_component/custom_component.py", line 11, in <module>
    from langflow.helpers.flow import list_flows, load_flow, run_flow
  File "/usr/local/lib/python3.10/site-packages/langflow/helpers/flow.py", line 8, in <module>
    from langflow.graph.schema import RunOutputs
  File "/usr/local/lib/python3.10/site-packages/langflow/graph/__init__.py", line 2, in <module>
    from langflow.graph.graph.base import Graph
  File "/usr/local/lib/python3.10/site-packages/langflow/graph/graph/base.py", line 14, in <module>
    from langflow.graph.graph.constants import lazy_load_vertex_dict
  File "/usr/local/lib/python3.10/site-packages/langflow/graph/graph/constants.py", line 2, in <module>
    from langflow.graph.vertex import types
  File "/usr/local/lib/python3.10/site-packages/langflow/graph/vertex/types.py", line 10, in <module>
    from langflow.graph.vertex.base import Vertex
  File "/usr/local/lib/python3.10/site-packages/langflow/graph/vertex/base.py", line 15, in <module>
    from langflow.interface.initialize import loading
  File "/usr/local/lib/python3.10/site-packages/langflow/interface/initialize/loading.py", line 10, in <module>
    from langflow.custom import Component, CustomComponent
ImportError: cannot import name 'Component' from partially initialized module 'langflow.custom' (most likely due to a circular import) (/usr/local/lib/python3.10/site-packages/langflow/custom/__init__.py)

I am wondering if I made a mistake loading the custom component or if it is currently not possible to load it due to the above issue (circular import).

[dosubot[bot]]

Hey @KSH94, I'm here to help you out! I'm a bot that can assist with bugs, questions, and even guide you on how to become a contributor. Let's squash those bugs together! 🤖

To resolve the circular import issue when trying to load a custom component in Langflow, you can use the __getattr__ function to lazily import the necessary classes only when they are accessed. This approach helps avoid circular imports. Here's how you can do it:

1. Define functions to import the classes you need (e.g., _import_input_class for Input and _import_output_class for Output).
2. Use the __getattr__ function to check if the requested attribute is one of the classes that might cause a circular import.
3. If it is, call the corresponding import function to load the class dynamically.

Here is the relevant part of the code that handles this:

def _import_input_class():
    from langflow.template.field.base import Input
    return Input

def _import_output_class():
    from langflow.template.field.base import Output
    return Output

def __getattr__(name: str) -> Any:
    # This is to avoid circular imports
    if name == "Input":
        return _import_input_class()
    elif name == "Output":
        return _import_output_class()
    # The other names should work as if they were imported from constants
    from . import constants
    return getattr(constants, name)

By using this approach, you can avoid circular import issues while still being able to access the necessary components dynamically ^[1].

Make sure to update your custom component script accordingly and try loading it again. This should resolve the circular import issue and allow your custom component to appear in the Langflow UI.

To continue talking to Dosu, mention @dosu.