Linting issue and using try and except block for error handling, and using UnsignedMetadataError from tuf.api.exceptions`

Signed-off-by: Kapil Sharma <ks3913688@gmail.com>

Author: h4l0gen

tuf/repository/_repository.py

@@ -9,6 +9,7 @@
 from copy import deepcopy
 from typing import Dict, Generator, Optional, Tuple
 
+from tuf.api.exceptions import UnsignedMetadataError
 from tuf.api.metadata import (
     Metadata,
     MetaFile,
@@ -191,9 +192,13 @@ def do_snapshot(
         root = self.root()
         snapshot_md = self.open(Snapshot.type)
 
-        if not root.verify_delegate(
-            Snapshot.type, snapshot_md.signed_bytes(), snapshot_md.signatures
-        ):
+        try:
+            root.verify_delegate(
+                Snapshot.type,
+                snapshot_md.signed_bytes,
+                snapshot_md.signatures,
+            )
+        except UnsignedMetadataError:
             update_version = True
 
         with self.edit_snapshot() as snapshot:
@@ -240,9 +245,13 @@ def do_timestamp(
         root = self.root()
         timestamp_md = self.open(Timestamp.type)
 
-        if not root.verify_delegate(
-            Timestamp.type, timestamp_md.signed_bytes(), timestamp_md.signatures
-        ):
+        try:
+            root.verify_delegate(
+                Timestamp.type,
+                timestamp_md.signed_bytes,
+                timestamp_md.signatures,
+            )
+        except UnsignedMetadataError:
             update_version = True
 
         with self.edit_timestamp() as timestamp: