app.py

"""Minimal repro isolating how gr.Examples handles None in optional image columns.

Hypothesis under test
---------------------
gr.Examples drops any INPUT COLUMN that is None in *every* example row (it builds
an `input_has_examples` mask, keeps a column only if at least one row is non-None,
then filters the value rows to match). When a whole column is dropped, the click
handler that loads an example back into the inputs returns fewer values than there
are output components -> ValueError: "didn't return enough output values".

Claim: a lone None in a *surviving* column (one that has >=1 non-None value across
the rows) is fine. Only an *entirely*-None column breaks.

This Space demonstrates the SAFE case (option 2). The optional second image column
has a real image in row 1, so the column survives; row 2's None loads cleanly.

To reproduce the FAILURE, swap in the BROKEN_EXAMPLES block below (both rows None
for img2) and redeploy -> you'll get the ValueError on example click / cache warm.
"""

import gradio as gr

SAFE_EXAMPLES = [
    # [label, img1, img2]  -- img2 column survives because row 1 fills it.
    ["both images", "red.png", "green.png"],
    ["only first image (img2=None, but column survives)", "blue.png", None],
]

# BROKEN_EXAMPLES -- uncomment to reproduce the crash. img2 is None in EVERY row,
# so gr.Examples drops the img2 column and the loader returns 2 values for 3
# components -> "didn't return enough output values (needed: 3, returned: 2)".
# BROKEN_EXAMPLES = [
#     ["only first image", "red.png", None],
#     ["only first image", "blue.png", None],
# ]


def describe(label, img1, img2):
    n = sum(x is not None for x in (img1, img2))
    return f"label={label!r} | images provided: {n} | img1={'set' if img1 is not None else 'None'} | img2={'set' if img2 is not None else 'None'}"


with gr.Blocks() as demo:
    gr.Markdown(
        "# gr.Examples None-column repro\n"
        "Click each example. Both load without error because the `img2` column "
        "has at least one real image (row 1), so Gradio keeps the column and the "
        "`None` in row 2 loads fine. This is **option 2** from the fix guidance."
    )
    label = gr.Textbox(label="label")
    with gr.Row():
        img1 = gr.Image(label="image 1 (required)", type="filepath")
        img2 = gr.Image(label="image 2 (optional)", type="filepath")
    out = gr.Textbox(label="result")
    run = gr.Button("Describe", variant="primary")

    gr.Examples(
        examples=SAFE_EXAMPLES,
        inputs=[label, img1, img2],
        outputs=out,
        fn=describe,
        cache_examples=True,
    )

    run.click(describe, inputs=[label, img1, img2], outputs=out)

if __name__ == "__main__":
    demo.launch()