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Fix/loadimage reader exception #8854

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vikasreddy11 wants to merge 2 commits into from
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Fix/loadimage reader exception #8854

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28d930c
fix: raise exception when specified reader is not installed in LoadImage
vikasreddy11 May 13, 2026
0a9e990
fix: make ImageWriter error message format-aware for install hints
vikasreddy11 May 13, 2026
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13 changes: 12 additions & 1 deletion monai/data/image_writer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -116,7 +116,18 @@ def resolve_writer(ext_name, error_if_not_found=True) -> Sequence:
except Exception: # other writer init errors indicating it exists
avail_writers.append(_writer)
if not avail_writers and error_if_not_found:
raise OptionalImportError(f"No ImageWriter backend found for {fmt}.")
hints = {
"png": "pip install pillow",
"jpg": "pip install pillow",
"jpeg": "pip install pillow",
"nii": "pip install nibabel",
"nii.gz": "pip install nibabel",
"dcm": "pip install itk",
}
hint = hints.get(fmt.lstrip(".").lower(), "pip install pillow or pip install nibabel")
raise OptionalImportError(
f"No ImageWriter backend found for {fmt}. Try: {hint}."
)
writer_tuple = ensure_tuple(avail_writers)
SUPPORTED_WRITERS[fmt] = writer_tuple
return writer_tuple
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2 changes: 1 addition & 1 deletion monai/transforms/io/array.py
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Original file line number Diff line number Diff line change
Expand Up @@ -210,7 +210,7 @@ def __init__(
try:
self.register(the_reader(*args, **kwargs))
except OptionalImportError:
warnings.warn(
raise ImportError(
f"required package for reader {_r} is not installed, or the version doesn't match requirement."
)
Comment on lines +213 to 215
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@coderabbitai coderabbitai Bot May 13, 2026

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⚠️ Potential issue | 🟡 Minor | ⚡ Quick win

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
# Verify exception chaining at the modified site.
rg -n -A4 -B2 'except OptionalImportError' monai/transforms/io/array.py

Repository: Project-MONAI/MONAI

Length of output: 934

Chain the exception to preserve traceback context.

The OptionalImportError should be chained when raising ImportError; otherwise debugging is hindered.

Suggested patch 
                except OptionalImportError:
-                    raise ImportError(
-                        f"required package for reader {_r} is not installed, or the version doesn't match requirement."
-                    )
+                except OptionalImportError as err:
+                    raise ImportError(
+                        f"required package for reader {_r} is not installed, or the version doesn't match requirement."
+                    ) from err
🧰 Tools
🪛 Ruff (0.15.12)

[warning] 213-215: Within an except clause, raise exceptions with raise ... from err or raise ... from None to distinguish them from errors in exception handling

(B904)

🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@monai/transforms/io/array.py` around lines 213 - 215, The raised ImportError
in the reader-loading block should preserve the original exception context:
replace the bare raise ImportError(...) with a chained raise using the caught
OptionalImportError (e.g., raise ImportError(f"required package for reader {_r}
...") from e). Update the raise in the block that references _r so the
ImportError is raised "from" the caught OptionalImportError to preserve the
traceback.

except TypeError: # the reader doesn't have the corresponding args/kwargs
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