32. Hashing with hashlib

`hashlib` provides hash algorithms like SHA-256, common for content addressing, Merkle trees, and integrity checks.

python
import hashlib

digest = hashlib.sha256(b"hello").hexdigest()
# note: hash functions take bytes, not str -- encode first
hashlib.sha256("hello".encode()).hexdigest()

For a simple Merkle-style combine step: `hashlib.sha256(left + right).digest()` where `left`/`right` are raw bytes digests. `hashlib.new("ripemd160", data)` (when available) and `hashlib.sha3_256` cover algorithms used by various chains, though Ethereum addresses specifically use Keccak-256, which differs subtly from the standardized SHA3-256 and isn't in the stdlib.

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