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Raise ValueError instead of asserting on FTEX format count #9805

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Raise ValueError instead of asserting on FTEX format count #9805

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35d7af8
Raise ValueError instead of asserting on FTEX format count
ritsth Jul 21, 2026
b4a82a8
Specify "texture formats" in error message
ritsth Jul 22, 2026
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10 changes: 10 additions & 0 deletions Tests/test_file_ftex.py
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Original file line number Diff line number Diff line change
Expand Up @@ -38,3 +38,13 @@ def test_invalid_texture() -> None:
with pytest.raises(ValueError, match="Invalid texture compression format: 2"):
with Image.open(io.BytesIO(data)):
pass


def test_unsupported_texture_format_count() -> None:
with open("Tests/images/ftex_dxt1.ftc", "rb") as fp:
# Change the format count to an unsupported value
data = fp.read(20) + struct.pack("<i", 2)

with pytest.raises(ValueError, match="Unsupported number of texture formats: 2"):
with Image.open(io.BytesIO(data)):
pass
4 changes: 3 additions & 1 deletion src/PIL/FtexImagePlugin.py
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Expand Up @@ -82,7 +82,9 @@ def _open(self) -> None:

# Only support single-format files.
# I don't know of any multi-format file.
assert format_count == 1
if format_count != 1:
msg = f"Unsupported number of texture formats: {format_count}"
raise ValueError(msg)

format, where = struct.unpack("<2i", self.fp.read(8))
self.fp.seek(where)
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