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

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

Author: pre-commit-ci[bot]

blockchain/merkle_tree.py

@@ -91,4 +91,5 @@ def verify_proof(leaf: str, proof: list[str], root: str) -> bool:
 
 if __name__ == "__main__":
     import doctest
+
     doctest.testmod()