List of datatypes or Nested Models Not Displaying Correctly in `pydantic_input` form

[gaurav-brandscapes]

Checklist

• I have searched the existing issues for similar issues.
• I added a very descriptive title to this issue.
• I have provided sufficient information below to help reproduce this issue.

Summary

Description:

When using pydantic_input with lists (e.g., List[str]) or list of models, the form do not render correctly.
This issue occurs despite following the correct usage patterns from the [official examples], specifically the Complex Instance Model example. This behavior is observed for:

• Simple lists like List[str], List[int]
• List of Pydantic models

# Nested Pydantic Model
class NestedModel(BaseModel):
    id: int = Field(..., description="ID of the nested object")
    name: str = Field(..., description="Name of the nested object")

# Main ConfigModel
class ConfigModel(BaseModel):
    keys: List[str] = Field(..., description="List of keys used for lookup")
    value: str = Field(..., description="Value associated with the keys")
    nested_items: List[NestedModel] = Field(..., description="List of nested model instances")

The above models give the following form when used with pydantic_input method

Expected Behaviour

Reproducible Code Example

import streamlit as st
from pydantic import BaseModel, Field
from typing import List, Dict, Any
import streamlit_pydantic as sp

# Nested Pydantic Model
class NestedModel(BaseModel):
    id: int = Field(..., description="ID of the nested object")
    name: str = Field(..., description="Name of the nested object")

# Main ConfigModel
class ConfigModel(BaseModel):
    keys: List[str] = Field(..., description="List of keys used for lookup")
    value: str = Field(..., description="Value associated with the keys")
    nested_items: List[NestedModel] = Field(..., description="List of nested model instances")


# -------------------------
# Streamlit UI
# -------------------------
st.set_page_config(layout="wide")
st.title("ConfigModel Input Form")

# Pre-filled data (Optional)
data = {
    "keys": ["id1", "id2"],
    "value": "example_value",
    "metadata": [{"key": "meta1", "value": 100}, {"key": "meta2", "value": 200}],
    "nested_items": [{"id": 1, "name": "Item 1"}, {"id": 2, "name": "Item 2"}]
}

model_instance = ConfigModel(**data)

# Render the form using streamlit_pydantic
with st.form("config_model_form"):
    form_result = sp.pydantic_input(key="config_model", model=model_instance)
    submit_button = st.form_submit_button("Submit")

# Handle form submission
if submit_button:
    if form_result:
        try:
            validated_data = ConfigModel.model_validate(form_result).dict()
            st.success("Form submitted successfully!")
            st.json(validated_data, expanded=True)
        except Exception as e:
            st.error(f"Validation error: {str(e)}")
    else:
        st.warning("Form submission failed. Please check the inputs.")

Steps To Reproduce

1. Install dependencies from the provided requirements.txt.
2. Save the code as app.py.
3. Run the code using:

streamlit run app.py

Dependencies:

pydantic-core==2.27.2
pydantic==2.10.6
streamlit==1.42.1
streamlit-pydantic==0.6.1-rc.2
pydantic-extra-types==2.10.2
pydantic-settings==2.7.1

Expected Behavior

• The keys field should display as a list input with pre-filled values "id1", "id2".
• The nested_items field should render forms for each instance of the NestedModel within a list form.

Current Behavior

• The list input does not appear or behaves incorrectly.
• List of models within nested_items are not displayed as expected, and editing or adding new instances is not possible.

Is this a regression?

• Yes, this used to work in a previous version.

Debug info

• OS: Ubuntu 22.04
• Python: 3.9, 3.11
• Streamlit: 1.42.1
• Pydantic: 2.10.6
• streamlit-pydantic: 0.6.1-rc.2, 0.6.1-rc.3

Additional Information

Please advise on whether this is a compatibility issue or requires additional configuration. 😊

[musantro]

After some debugging, I found that when creating the buttons for "add item" streamlit raises an exception:

streamlit.errors.StreamlitAPIException: `st.button()` can't be used in an `st.form()`.
For more information, refer to the
[documentation for forms](https://docs.streamlit.io/develop/api-reference/execution-flow/st.form).

In fact, if you use the plain streamlit_pydantic.ui_renderer.InputUI.render_ui() outside of a st.form(), it displays correctly.

Possible related issues:

streamlit/streamlit#4077

[Rishikapanwar]

Hello @musantro ! Does it mean there is no way to handle list[str] fields inside st.form? Is there any way to exclude these specific fields from pydantic_input() and later manually add them in the form and update the pydantic class fields? I haven't found any workaround by looking at the documentation yet.

[musantro]

Hello @musantro ! Does it mean there is no way to handle list[str] fields inside st.form? Is there any way to exclude these specific fields from pydantic_input() and later manually add them in the form and update the pydantic class fields?

As the current implementation for List[Any] adds the "Add item", "Remove Item" buttons, it's not possible.

The alternative way is what you mentioned (and I did too), use a pydantic_input() instead.

If you want to set it form alike:

with st.container(border=True):
    my_model_modififed = sp.pydantic_input(...)
    st.button("Submit", on_click=callback, args=..., kwargs={...})