fix: Format

Author: tmathern

src/c2pa/c2pa.py

@@ -2269,10 +2269,11 @@ def sign_file(self,
 
         try:
             # Open source file and destination file, then use the sign method
-            with open(source_path, 'rb') as source_file, open(dest_path, 'w+b') as dest_file:
+            with open(source_path, 'rb') as source_file, \
+                 open(dest_path, 'w+b') as dest_file:
                 return self.sign(signer, mime_type, source_file, dest_file)
         except Exception as e:
-            raise C2paError(f"Error signing file: {str(e)}")
+            raise C2paError(f"Error signing file: {str(e)}") from e
 
 
 def format_embeddable(format: str, manifest_bytes: bytes) -> tuple[int, bytes]: