Fix px.imshow drawing the next animation frame in empty facet_col_wrap cells

CHANGELOG.md

@@ -7,6 +7,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 - Fix concurrent first access to lazily initialized graph object properties, which could raise `ValueError("Invalid value")` [[#3441](https://github.com/plotly/plotly.py/issues/3441)], with thanks to @hb1915 for the contribution!
 - Fix `px.sunburst`, `px.treemap` and `px.icicle` listing sectors in a different order on every run when `path` is used with a Polars DataFrame; sectors now follow their order of first appearance for all dataframe backends [[#5765](https://github.com/plotly/plotly.py/issues/5765)], with thanks to @Irahan2 for the contribution!
+- Fix `px.imshow` with `animation_frame` and `facet_col_wrap` drawing the first facet of the second animation frame in the empty cell of an incomplete facet grid, where it stayed while the animation played [[#5783](https://github.com/plotly/plotly.py/pull/5783)], with thanks to @breken-ai for the contribution!
 
 
 ## [7.1.0] - 2026-09-15

plotly/express/_imshow.py

@@ -611,7 +611,10 @@ def imshow(
     nslices_facets = nslices_facet_row * nslices_facet_col
     frame_list = []
     for index, trace in enumerate(traces):
-        if ((facet_col or facet_row) and index < nrows * ncols) or index == 0:
+        # Only the first animation frame goes into fig.data. With facet_col_wrap,
+        # nrows * ncols can exceed the number of facets, so compare with
+        # nslices_facets to leave the unused cells of the grid empty.
+        if ((facet_col or facet_row) and index < nslices_facets) or index == 0:
             # Calculate row and col position
             # index is ordered by (facet_row, facet_col) from itertools.product
             # When facet_col_wrap is used (and facet_row is None), traces are laid out

tests/test_optional/test_px/test_imshow.py

@@ -469,6 +469,25 @@ def test_animation_and_facet(binary_string):
     assert len(fig.data) == img.shape[1]
 
 
+@pytest.mark.parametrize("binary_string", [False, True])
+def test_animation_and_facet_col_wrap_incomplete_grid(binary_string):
+    # 5 facets wrapped in 2 columns leave the 6th cell of the 3x2 grid empty.
+    # That cell must stay empty, instead of showing the first facet of the
+    # second animation frame.
+    img = np.arange(2 * 5 * 3 * 4).reshape(2, 5, 3, 4).astype(np.uint8)
+    fig = px.imshow(
+        img,
+        animation_frame=0,
+        facet_col=1,
+        facet_col_wrap=2,
+        binary_string=binary_string,
+    )
+    nslices_facet = img.shape[1]
+    assert len(fig.frames) == img.shape[0]
+    assert len(fig.data) == nslices_facet
+    assert [trace.name for trace in fig.data] == [str(i) for i in range(5)]
+
+
 @pytest.mark.parametrize("facet_row", [0, 1, 2, -1])
 @pytest.mark.parametrize("binary_string", [False, True])
 def test_facet_row(facet_row, binary_string):