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bqn-safetensors

BQN library to read and write arrays stored in the safetensors format.

Why safetensors?

Safetensors is a format to store multidimensional arrays (tensors) in a safe, efficient way. Compared the NPY format (see bqn-npy), it has the advantage of being able to store multiple named arrays in a single file, and being able to read an array without loading the entire file in memory.

Supported array types

This library can load arrays stored with any dtype supported by the official library. However, it can only store arrays in 32-bit signed integers (I32) and double-precision floating point (F64), which are the native types of CBQN.

Format	Description	Deserialization	Serialization
BOOL	Boolean type	✅	❌
U8	Unsigned byte	✅	❌
I8	Signed byte	✅	❌
F8_E5M4	FP8	✅	❌
F8_E4M3	FP8	✅	❌
I16	Signed integer (16-bit)	✅	❌
U16	Unsigned integer (16-bit)	✅	❌
F16	Half-precision floating point	✅	❌
BF16	Brain floating point	✅	❌
I32	Signed integer (32-bit)	✅	✅
U32	Unsigned integer (32-bit)	✅	❌
F32	Floating point (32-bit)	✅	❌
F64	Floating point (64-bit)	✅	✅
I64	Signed integer (64-bit)	✅	❌
U64	Unsigned integer (64-bit)	✅	❌

Usage

⟨ExtractMetadata,GetArrayNames,GetArray,SerializeArrays⟩←•Import"safetensors.bqn"

# Use •file.MapBytes to avoid loading the entire file in memory, using memory-mapping instead.
bytes←•file.MapBytes"input.safetensors"

# Extract the metadata (a string -> string map) from the file.
ExtractMetadata bytes

# List the arrays present in the file.
GetArrayNames bytes

# Read an array from the file.
bytes GetArray "my_array"

# Create arrays and save them to a safetensors file.
a←3‿4‿5⥊↕60    # will be stored as I32
b←2‿3⥊3.14×↕6  # will be stored as F64
"output.safetensors"•file.Bytes "arr_a"‿"arr_b" SerializeArrays a‿b

How to test

The script gentest.py generates a test safetensors file (arrs.safetensors) containing arrays of various shapes and dtypes. It requires numpy and safetensors dependencies. The easiest way to run it is via uv run, which takes care of installing the dependencies in an isolated environment automatically:

uv run gentest.py

The script test.bqn then reads this test file and displays its contents to check that they are identical to the ones reported by Python. It also creates another set of arrays, serializes them to a test.safetensors file, and deserializes it again.

bqn test.bqn

Finally, the script loadtest.py reads the BQN-generated safetensors file to ensure that it is readable from Python.

uv run loadtest.py