fix bug on merging captures

Author: Teque5

sigmf/__init__.py

@@ -5,7 +5,7 @@
 # SPDX-License-Identifier: LGPL-3.0-or-later
 
 # version of this python module
-__version__ = "1.7.0"
+__version__ = "1.7.1"
 # matching version of the SigMF specification
 __specification__ = "1.2.6"
 

sigmf/sigmffile.py

@@ -507,9 +507,9 @@ def add_capture(self, start_index, metadata=None):
         new_capture[self.START_INDEX_KEY] = start_index
         # merge if capture exists
         merged = False
-        for existing_capture in self._metadata[self.CAPTURE_KEY]:
+        for idx, existing_capture in enumerate(self._metadata[self.CAPTURE_KEY]):
             if existing_capture[self.START_INDEX_KEY] == start_index:
-                existing_capture = dict_merge(existing_capture, new_capture)
+                self._metadata[self.CAPTURE_KEY][idx] = dict_merge(existing_capture, new_capture)
                 merged = True
         if not merged:
             capture_list += [new_capture]

tests/test_sigmffile.py

@@ -366,6 +366,31 @@ def test_add_capture():
     sigf.add_capture(start_index=0, metadata={})
 
 
+def test_add_capture_metadata_merge():
+    '''test that adding capture with existing start_index properly merges metadata'''
+    sigf = SigMFFile()
+    
+    # add initial capture with some metadata
+    initial_meta = {"core:frequency": 915e6, "core:sample_rate": 1e6}
+    sigf.add_capture(start_index=0, metadata=initial_meta)
+    
+    # add capture with same start_index but additional metadata
+    additional_meta = {"core:datetime": "2026-03-17T10:00:00Z", "custom:gain": 30}
+    sigf.add_capture(start_index=0, metadata=additional_meta)
+    
+    # verify metadata was merged properly
+    captures = sigf.get_captures()
+    assert len(captures) == 1, "should have exactly one capture"
+    
+    merged_capture = captures[0]
+    # original metadata should be preserved
+    assert merged_capture["core:frequency"] == 915e6
+    assert merged_capture["core:sample_rate"] == 1e6
+    # new metadata should be added
+    assert merged_capture["core:datetime"] == "2026-03-17T10:00:00Z"
+    assert merged_capture["custom:gain"] == 30
+
+
 def test_add_annotation():
     sigf = SigMFFile()
     sigf.add_capture(start_index=0)