fast-hash-utils 0.6.0

Fast deterministic dict hashing via mypyc

hash-utils

Fast deterministic dict hashing via mypyc, plus a 64-bit FNV-1a hash for strings and bytes.

All hashing is deterministic across processes — immune to PYTHONHASHSEED randomization.

Functions

• dict_hash(d) — deterministic hash of a nested dict's full content (keys + values)
• shape_hash(d) — structural hash that ignores string/int/float values, only hashing keys, value types, bools, and structure
• fnv64(data) — fast 64-bit FNV-1a hash for str/bytes/bytearray (C extension)

Install

pip install fast-hash-utils

Usage

from hash_utils import dict_hash, shape_hash, fnv64

d1 = {"name": "alice", "config": {"enabled": True, "tags": []}}
d2 = {"name": "bob",   "config": {"enabled": True, "tags": []}}

# Full content hash — different names produce different hashes
dict_hash(d1) != dict_hash(d2)

# Shape hash — same structure produces same hash
shape_hash(d1) == shape_hash(d2)

# Fast 64-bit hash for strings and bytes
fnv64(b"hello world")
fnv64("hello world")

Why

shape_hash enables massive deduplication for jsonschema validation. If 13,000 dicts share the same structure but differ only in string values, they collapse to 1 unique shape — skip 12,999 redundant validations.

fnv64 provides a fast non-cryptographic 64-bit hash — 2x faster than dual-crc32, with zero expected collisions under 5 billion inputs. Accepts str (zero-copy UTF-8) and bytes.

Performance

Dict traversal compiled via mypyc to native C. fnv64 is a C extension using PyUnicode_AsUTF8AndSize for zero-copy string access.

Method	ops/s	Notes
fnv64 (C)	2,000K	64-bit, str/bytes
2x zlib.crc32 → str	950K	64-bit via concatenation
shape_hash (mypyc)	320K	nested dict structure
dict_hash (mypyc)	250K	nested dict full content
json.dumps + hash	115K	stdlib baseline

Development

python -m venv .venv && source .venv/bin/activate
make install    # editable install with dev deps
make test       # run tests (pure Python or compiled)
make bench      # run benchmarks
make style      # ruff check --fix + format
make clean      # remove build artifacts

License

MIT