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Backport PR #29931 on branch v3.10.x (Allow Python native sequences in Matplotlib imsave().) #29933

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Merged
merged 2 commits into from
Apr 20, 2025
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Backport PR #29931 on branch v3.10.x (Allow Python native sequences in Matplotlib imsave().) #29933

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Backport PR #29931: Allow Python native sequences in Matplotlib `imsa…
ksunden Apr 17, 2025
4cd3b06
STY: placate lint
tacaswell Apr 18, 2025
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7 changes: 6 additions & 1 deletion lib/matplotlib/image.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1536,7 +1536,8 @@ def imsave(fname, arr, vmin=None, vmax=None, cmap=None, format=None,
extension of *fname*, if any, and from :rc:`savefig.format` otherwise.
If *format* is set, it determines the output format.
arr : array-like
The image data. The shape can be one of
The image data. Accepts NumPy arrays or sequences
(e.g., lists or tuples). The shape can be one of
MxN (luminance), MxNx3 (RGB) or MxNx4 (RGBA).
vmin, vmax : float, optional
*vmin* and *vmax* set the color scaling for the image by fixing the
Expand Down Expand Up @@ -1567,6 +1568,10 @@ def imsave(fname, arr, vmin=None, vmax=None, cmap=None, format=None,
default 'Software' key.
"""
from matplotlib.figure import Figure

# Normalizing input (e.g., list or tuples) to NumPy array if needed
arr = np.asanyarray(arr)

if isinstance(fname, os.PathLike):
fname = os.fspath(fname)
if format is None:
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22 changes: 22 additions & 0 deletions lib/matplotlib/tests/test_image.py
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Expand Up @@ -184,6 +184,28 @@ def test_imsave(fmt):
assert_array_equal(arr_dpi1, arr_dpi100)


def test_imsave_python_sequences():
# Tests saving an image with data passed using Python sequence types
# such as lists or tuples.

# RGB image: 3 rows × 2 columns, with float values in [0.0, 1.0]
img_data = [
[(1.0, 0.0, 0.0), (0.0, 1.0, 0.0)],
[(0.0, 0.0, 1.0), (1.0, 1.0, 0.0)],
[(0.0, 1.0, 1.0), (1.0, 0.0, 1.0)],
]

buff = io.BytesIO()
plt.imsave(buff, img_data, format="png")
buff.seek(0)
read_img = plt.imread(buff)

assert_array_equal(
np.array(img_data),
read_img[:, :, :3] # Drop alpha if present
)


@pytest.mark.parametrize("origin", ["upper", "lower"])
def test_imsave_rgba_origin(origin):
# test that imsave always passes c-contiguous arrays down to pillow
Expand Down
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