[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Author: pre-commit-ci[bot]

blockchain/simple_blockchain.py

@@ -44,7 +44,9 @@ def compute_hash(self, nonce: int) -> str:
         Returns:
             str: Hexadecimal hash string.
         """
-        block_string = f"{self.index}{self.timestamp}{self.data}{self.previous_hash}{nonce}"
+        block_string = (
+            f"{self.index}{self.timestamp}{self.data}{self.previous_hash}{nonce}"
+        )
         return hashlib.sha256(block_string.encode()).hexdigest()
 
     def mine_block(self, difficulty: int) -> Tuple[int, str]:
@@ -64,7 +66,7 @@ def mine_block(self, difficulty: int) -> Tuple[int, str]:
         if difficulty < 1:
             raise ValueError("Difficulty must be at least 1")
         nonce = 0
-        target = '0' * difficulty
+        target = "0" * difficulty
         while True:
             hash_result = self.compute_hash(nonce)
             if hash_result.startswith(target):
@@ -152,7 +154,7 @@ def is_valid(self) -> bool:
             prev = self.chain[i - 1]
             if current.previous_hash != prev.hash:
                 return False
-            if not current.hash.startswith('0' * self.difficulty):
+            if not current.hash.startswith("0" * self.difficulty):
                 return False
             if current.hash != current.compute_hash(current.nonce):
                 return False