Multihash for Python

3.0.0 · active · verified Thu Apr 16

py-multihash is a Python implementation of the Multihash specification, providing functions to encode and decode self-describing cryptographic hashes. The current version is 3.0.0. Releases are infrequent, tied to updates in the Multiformats specification.

Common errors

```
AttributeError: module 'multihash' has no attribute 'Multihash'
```
cause Attempting to use the `Multihash` class which was removed in v3.0.0.

fix The `encode` and `decode` functions are now top-level. Use `multihash.encode(...)` and `multihash.decode(...)` directly.
```
ImportError: cannot import name 'constants' from 'multihash'
```
cause Attempting to import the `constants` module which was removed in v3.0.0.

fix Algorithm constants are now part of the `py-multicodec` library. Use `import multicodec` and access constants like `multicodec.SHA2_256`.
```
TypeError: encode() missing 1 required positional argument: 'data' (if called as `Multihash.encode(alg)`) or AttributeError: type object 'Multihash' has no attribute 'encode'
```
cause Attempting to call `encode` or `decode` as a method of the removed `Multihash` class, or statically without providing `self`.

fix These are now top-level functions. Call them as `multihash.encode(data, alg)` or `multihash.decode(mh)`.

Warnings

breaking The `Multihash` class has been removed in version 3.0.0. `encode` and `decode` are now top-level functions in the `multihash` module, and `Digest` is a directly exposed class.
Fix: Replace `Multihash().encode(data, code)` with `multihash.encode(data, code)`. Replace `Multihash().decode(mh)` with `multihash.decode(mh)`. Import `Digest` directly: `from multihash import Digest`.
breaking The `multihash.constants` module was removed in version 3.0.0. All algorithm constants (e.g., `SHA2_256`) are now provided by the `py-multicodec` library.
Fix: Instead of `from multihash.constants import SHA2_256`, use `import multicodec` and refer to constants as `multicodec.SHA2_256`.
breaking Python 3.10 or newer is now required for `py-multihash` version 3.0.0 and above.
Fix: Upgrade your Python environment to 3.10 or higher. If unable, pin `py-multihash<3.0.0`.
gotcha The `multihash.encode` function expects the hash algorithm to be specified by its string name (e.g., 'sha2-256') or its integer code, not a `py-multicodec` constant directly for the algorithm parameter.
Fix: Use `multihash.encode(data, 'sha2-256')` or `multihash.encode(data, 0x12)` instead of `multihash.encode(data, multicodec.SHA2_256)` directly for the algorithm name/code parameter. The `multicodec` library is still essential for looking up constants and verifying codes.

Install

pip install py-multihash Install py-multihash

Imports

encode
```
from multihash import encode
```
decode
```
from multihash import decode
```
Digest
```
from multihash import Digest
```
Multihash
wrong:
```
from multihash import Multihash
```
correct:
```
from multihash import encode, decode, Digest
```
The `Multihash` class was removed in v3.0.0. `encode` and `decode` are now top-level module functions, and `Digest` is directly importable.

Quickstart

This example demonstrates how to encode a byte string into a multihash and then decode it back to retrieve its properties like the algorithm name, code, length, and the raw digest.

import multihash
import multicodec

# Encode a byte string with a specific hash algorithm
data = b'Hello multihash world!'
mh = multihash.encode(data, 'sha2-256')
print(f"Encoded multihash: {mh.hex()}")

# Decode a multihash digest
decoded_digest = multihash.decode(mh)
print(f"Decoded digest name: {decoded_digest.name}")
print(f"Decoded digest code: {hex(decoded_digest.code)}")
print(f"Decoded digest length: {decoded_digest.length}")
print(f"Original digest: {decoded_digest.digest.hex()}")

# Verify the algorithm code using multicodec constants
assert decoded_digest.code == multicodec.SHA2_256
print("Verification successful!")

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