Merge pull request #18907 from meeseeksmachine/auto-backport-of-pr-18882-on-v7.2.x

astrofrog · web-flow · commit 4136ed12de3f · 2025-11-14T15:12:03.000Z
Backport PR #18882 on branch v7.2.x (BUG: warn instead of raise when failing to read specific files in fitsdiff script)
diff --git a/astropy/io/fits/scripts/fitsdiff.py b/astropy/io/fits/scripts/fitsdiff.py
@@ -400,20 +400,29 @@ def main(args=None):
     try:
         for a, b in files:
             # TODO: pass in any additional arguments here too
-            diff = fits.diff.FITSDiff(
-                a,
-                b,
-                ignore_hdus=opts.ignore_hdus,
-                ignore_keywords=opts.ignore_keywords,
-                ignore_comments=opts.ignore_comments,
-                ignore_fields=opts.ignore_fields,
-                numdiffs=opts.numdiffs,
-                rtol=opts.rtol,
-                atol=opts.atol,
-                ignore_blanks=opts.ignore_blanks,
-                ignore_blank_cards=opts.ignore_blank_cards,
-            )
-
+            try:
+                diff = fits.diff.FITSDiff(
+                    a,
+                    b,
+                    ignore_hdus=opts.ignore_hdus,
+                    ignore_keywords=opts.ignore_keywords,
+                    ignore_comments=opts.ignore_comments,
+                    ignore_fields=opts.ignore_fields,
+                    numdiffs=opts.numdiffs,
+                    rtol=opts.rtol,
+                    atol=opts.atol,
+                    ignore_blanks=opts.ignore_blanks,
+                    ignore_blank_cards=opts.ignore_blank_cards,
+                )
+            except OSError:
+                if not opts.quiet:
+                    msg = f"Warning: failed to open {a}"
+                    if b != a:
+                        msg += f" (or {b})"
+                    msg += ". Skipping."
+                    print(msg, file=sys.stderr)
+                identical.append(None)
+                continue
             diff.report(fileobj=out_file)
             identical.append(diff.identical)
 
diff --git a/astropy/io/fits/tests/test_fitsdiff.py b/astropy/io/fits/tests/test_fitsdiff.py
@@ -11,6 +11,7 @@
 from astropy.io.fits.convenience import writeto
 from astropy.io.fits.hdu import PrimaryHDU, hdulist
 from astropy.io.fits.scripts import fitsdiff
+from astropy.utils.compat.optional_deps import HAS_UNCOMPRESSPY
 from astropy.utils.misc import _NOT_OVERWRITING_MSG_MATCH
 
 from .conftest import FitsTestCase
@@ -236,7 +237,6 @@ def test_quiet(self, capsys):
         assert out == ""
         assert err == ""
 
-    @pytest.mark.slow
     def test_path(self, capsys):
         os.mkdir(self.temp("sub/"))
         tmp_b = self.temp("sub/ascii.fits")
@@ -256,7 +256,9 @@ def test_path(self, capsys):
         tmp_d = self.temp("sub/")
         assert fitsdiff.main(["-q", self.data_dir, tmp_d]) == 1
         assert fitsdiff.main(["-q", tmp_d, self.data_dir]) == 1
-        assert fitsdiff.main(["-q", self.data_dir, self.data_dir]) == 0
+
+        expected_retv = int(not HAS_UNCOMPRESSPY)
+        assert fitsdiff.main(["-q", self.data_dir, self.data_dir]) == expected_retv
 
         # no match
         tmp_c = self.data("arange.fits")
@@ -273,6 +275,43 @@ def test_path(self, capsys):
         assert fitsdiff.main(["-q", tmp_f, self.data_dir]) == 0
         assert fitsdiff.main(["-q", self.data_dir, tmp_f]) == 0
 
+    @pytest.mark.filterwarnings("ignore:unclosed file:ResourceWarning")
+    def test_warning_unreadable_file(self, capsys, monkeypatch):
+        # simulate not having uncompresspy installed regardless of the actual state
+        monkeypatch.setattr(fits.file, "HAS_UNCOMPRESSPY", False)
+
+        Zfile = self.data("lzw.fits.Z")
+        assert fitsdiff.main([Zfile, Zfile]) != 0
+        out, err = capsys.readouterr()
+        assert out == ""
+        assert err == f"Warning: failed to open {Zfile}. Skipping.\n"
+
+        os.mkdir(self.temp("sub/"))
+        tmp = self.temp("sub/ascii.fits")
+        tmp_h = self.data("group.fits")
+        with hdulist.fitsopen(tmp_h) as hdu:
+            hdu.writeto(tmp)
+
+        assert fitsdiff.main([Zfile, tmp]) != 0
+        out, err = capsys.readouterr()
+        assert out == ""
+        assert err == f"Warning: failed to open {Zfile} (or {tmp}). Skipping.\n"
+
+        assert fitsdiff.main(["-q", Zfile, tmp]) != 0
+        out, err = capsys.readouterr()
+        assert out == ""
+        assert err == ""
+
+        assert fitsdiff.main([tmp, Zfile]) != 0
+        out, err = capsys.readouterr()
+        assert out == ""
+        assert err == f"Warning: failed to open {tmp} (or {Zfile}). Skipping.\n"
+
+        assert fitsdiff.main(["-q", tmp, Zfile]) != 0
+        out, err = capsys.readouterr()
+        assert out == ""
+        assert err == ""
+
     def test_ignore_hdus(self):
         a = np.arange(100).reshape(10, 10)
         b = a.copy() + 1
diff --git a/docs/changes/io.fits/18882.bugfix.rst b/docs/changes/io.fits/18882.bugfix.rst
@@ -0,0 +1,3 @@
+Fixed a bug in ``fitsdiff`` script where failing to read a single file could
+crash the entire program. A warning is now printed instead, and such files
+are simply ignored.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+Fixed a bug in ``fitsdiff`` script where failing to read a single file could
	`2`	`+crash the entire program. A warning is now printed instead, and such files`
	`3`	`+are simply ignored.`