Altair fails to render chart out of pandas dataframe on Streamlit

Question

I have the following code in Python, using Streamlit as framework:

try:
    native_data = data.copy()
    
    # Create Altair chart with native data
    st.write(f"Debug: Native data type: {type(native_data)}")
    chart = alt.Chart(native_data).mark_bar().encode(
        x=alt.X(x_col, type='nominal'),
        y=alt.Y(y_col, type='quantitative')
    ).properties(
        title=self._label,
        width=400,
        height=300
    )
    
except Exception as chart_creation_error:
    st.write(f"Debug: Chart creation error: {chart_creation_error}")
    return "table_only"

try:
    container.altair_chart(chart, use_container_width=True)
    return "success"
    
except Exception as render_error:
    st.write(f"Debug: Chart rendering error: {render_error}")
    st.write(f"Debug: Render error type: {type(render_error)}")
    import traceback
    st.write("Debug: Render error traceback:")
    st.code(traceback.format_exc())
    raise render_error

And this is the debug output:

Debug: Native data type: <class 'pandas.core.frame.DataFrame'>

Debug: Chart rendering error: You passed a <class 'narwhals.stable.v1.DataFrame'> to is_pandas_dataframe.

I can see that the dataframe used to generate the Altair object is a Pandas dataframe but, nevertheless, Altair seems to confuse it with a Narwhals dataframe.

I haven't found a single reference to a similar case, so any help will be much appreciated.

The only thing that I found is github. But also I think, you can pass data to Altair in the form of a dictionary. (Not correctly - but works) alt.Chart(native_data.to_dict('records'))... — Sindik
– Sindik, Commented Jul 26 at 19:17
@Sindik it doesn't work, I get this error: UserWarning: data of type <class 'list'> not recognized warnings.warn(f"data of type {type(data)} not recognized", stacklevel=1) — HuLu ViCa
– HuLu ViCa, Commented Jul 26 at 19:49
@HuLu Vica try to convert your data in advance into the altair.Data class - it accepts a list of dictionaries as input. You can try. Here is such code. new_data = alt.Data(values=native_data.to_dict()) chart = alt.Chart(new_data) — Sindik
– Sindik, Commented Jul 27 at 6:52
@HuLuViCa can you make a fully reproducible example please? From the same discussion on github, it looks like this is easy to fix, it just needs a reproducer. The code you've pasted isn't even runnable — ignoring_gravity
– ignoring_gravity, Commented Jul 28 at 15:43

ignoring_gravity · Accepted Answer · 2025-07-28 15:48:33Z

0

Looks like this is a bug in Altair==5.4.0

import streamlit as st
import altair as alt
import pandas as pd

native_data = pd.DataFrame({'a': [1,2,3], 'b': [4,5,6]})
x_col = 'a'
y_col = 'b'

# Create Altair chart with native data
st.write(f"Debug: Native data type: {type(native_data)}")
chart = alt.Chart(native_data).mark_bar().encode(
   x=alt.X(x_col, type='nominal'),
   y=alt.Y(y_col, type='quantitative')
).properties(
   title='foo',
   width=400,
   height=300
)
   
st.container().altair_chart(chart, use_container_width=True)

TypeError: You passed a `<class 'narwhals.stable.v1.DataFrame'>` to `is_pandas_dataframe`.

Hint: Instead of e.g. `is_pandas_dataframe(df)`, did you mean `is_pandas_dataframe(df.to_native())`?

If you upgrade your Altair version to at least 5.5.0, then it should pass

answered Jul 28 at 15:48

ignoring_gravity

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