add extract_meta

csst_common/io.py

@@ -108,6 +108,24 @@ def append_meta(hdulist: fits.HDUList, **kwargs) -> fits.HDUList:
     return hdulist
 
 
+def extract_meta(hdulist: fits.HDUList) -> dict:
+    """
+    Extract meta from hdulist.
+
+    Parameters
+    ----------
+    hdulist : fits.HDUList
+        HDUList.
+
+    Returns
+    -------
+    dict
+        Meta data.
+    """
+    meta = json.loads(hdulist[0].header["META"])
+    return meta
+
+
 def verify_checksum(file_path) -> bool:
     """
     Verify a .fits file via checksum.

tests/test_fits_header_ops.py

@@ -20,6 +20,7 @@ from csst_common.io import (
     get_proc_info,
     generate_meta,
     append_meta,
+    extract_meta,
 )
 
 
@@ -139,8 +140,8 @@ class TestFitsHeaderOps(unittest.TestCase):
             generate_meta(obs_id=1)
 
     def test_append_meta(self):
-        hdulist = fits.HDUList()
-        hdulist.append(fits.PrimaryHDU())
+        hdulist = fits.HDUList([fits.PrimaryHDU()])
         hdulist = append_meta(hdulist, obs_id="123456")
-        self.assertIn("OBS_ID", hdulist[0].header)
-        self.assertEqual(hdulist[0].header["OBS_ID"], "123456")
+        self.assertIn("META", set(hdulist[0].header.keys()))
+        meta = extract_meta(hdulist)
+        self.assertEqual(meta["obs_id"], "123456")