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Building with Python

The encoderfile Python package lets you build encoderfile binaries programmatically — no separate CLI installation required. It is a thin wrapper around the same Rust build pipeline used by the CLI tool.

Installation

pip install encoderfile

# or with uv
uv add encoderfile

Prerequisites

You need an ONNX-exported model directory containing:

model.onnx — ONNX model weights
tokenizer.json — tokenizer vocabulary and configuration
config.json — model architecture metadata

Export any HuggingFace model with Optimum:

pip install 'optimum[onnx]'
optimum-cli export onnx \
  --model distilbert-base-uncased-finetuned-sst-2-english \
  --task text-classification \
  ./sentiment-model

Quick Start

The simplest build uses EncoderfileBuilder directly:

from encoderfile import EncoderfileBuilder, ModelType

builder = EncoderfileBuilder(
    name="sentiment-analyzer",
    model_type=ModelType.SequenceClassification,
    path="./sentiment-model",  # path to your ONNX-exported model directory
)
builder.build()
# writes ./sentiment-analyzer.encoderfile

Three Ways to Build

1. EncoderfileBuilder (full control)

Best when you need fine-grained control over tokenizer settings, transforms, or cross-compilation targets.

from encoderfile import EncoderfileBuilder, ModelType, TokenizerBuildConfig, Fixed

builder = EncoderfileBuilder(
    name="my-ner-model",
    model_type=ModelType.TokenClassification,
    path="./ner-model",
    output_path="./build/my-ner-model.encoderfile",
    version="1.2.0",
    tokenizer=TokenizerBuildConfig(
        pad_strategy=Fixed(n=512),
        max_length=512,
    ),
)
builder.build()

2. build() convenience function (flat arguments)

Best for scripts where you want to avoid importing supporting classes.

from encoderfile import build, ModelType

build(
    name="my-embedder",
    model_type=ModelType.Embedding,
    path="./embedding-model",
    output_path="./my-embedder.encoderfile",
    tokenizer_pad_to="batch_longest",
    tokenizer_max_length=256,
)

3. build_from_config() (YAML config file)

Best when your build configuration lives in a file alongside your model.

from encoderfile import build_from_config

build_from_config("sentiment-config.yml")

Where sentiment-config.yml contains:

encoderfile:
  name: sentiment-analyzer
  path: ./sentiment-model
  model_type: sequence_classification
  output_path: ./build/sentiment-analyzer.encoderfile

Model Types

See the Building Guide for a full description of each model type, including supported HuggingFace AutoModel classes and inference output shapes.

ModelType values are plain strings (StrEnum), so you can pass the string directly instead of importing the enum:

builder = EncoderfileBuilder(
    name="my-model",
    model_type="sequence_classification",
    path="./my-model",
)

Tokenizer Configuration

Override tokenizer padding and truncation settings at build time with TokenizerBuildConfig. These settings are baked into the binary and applied at every inference call.

from encoderfile import EncoderfileBuilder, ModelType, TokenizerBuildConfig, BatchLongest, Fixed

# Dynamic padding — each batch is padded to its longest sequence
tokenizer = TokenizerBuildConfig(pad_strategy=BatchLongest())

# Fixed-length padding — every sequence padded/truncated to exactly 512 tokens
tokenizer = TokenizerBuildConfig(
    pad_strategy=Fixed(n=512),
    max_length=512,
    truncation_side="right",
    truncation_strategy="longest_first",
)

builder = EncoderfileBuilder(
    name="my-model",
    model_type=ModelType.Embedding,
    path="./my-model",
    tokenizer=tokenizer,
)
builder.build()

When using the build() convenience function, use flat tokenizer_* arguments instead:

from encoderfile import build, ModelType

build(
    name="my-model",
    model_type=ModelType.Embedding,
    path="./my-model",
    tokenizer_pad_to=512,          # int → Fixed(n=512), or "batch_longest"
    tokenizer_max_length=512,
    tokenizer_truncation_side="right",
)

Lua Transforms

Embed a Lua post-processing script to transform model logits before they are returned. See the Transforms guide for the full scripting API.

from encoderfile import EncoderfileBuilder, ModelType

# Inline Lua string
builder = EncoderfileBuilder(
    name="normalized-embedder",
    model_type=ModelType.Embedding,
    path="./embedding-model",
    transform="function Postprocess(logits) return logits:lp_normalize(2.0, 2.0) end",
)
builder.build()

# From a file — use the build() convenience function
from encoderfile import build, ModelType

build(
    name="normalized-embedder",
    model_type=ModelType.Embedding,
    path="./embedding-model",
    transform_path="./normalize.lua",
)

Cross-compilation

Build a binary targeting a different platform by passing a target triple:

from encoderfile import EncoderfileBuilder, ModelType

builder = EncoderfileBuilder(
    name="my-model",
    model_type=ModelType.Embedding,
    path="./my-model",
    target="x86_64-unknown-linux-gnu",  # build for Linux on a Mac
)
builder.build()

You can also use a TargetSpec object:

from encoderfile import EncoderfileBuilder, ModelType, TargetSpec

spec = TargetSpec("aarch64-apple-darwin")
print(spec.arch, spec.os, spec.abi)  # "aarch64", "apple", "darwin"

builder = EncoderfileBuilder(
    name="my-model",
    model_type=ModelType.Embedding,
    path="./my-model",
    target=spec,
)
builder.build()

Inspecting a Binary

Use read_metadata() to read the metadata embedded in an existing encoderfile binary without running inference:

from encoderfile import read_metadata

info = read_metadata("./sentiment-analyzer.encoderfile")

print(info.encoderfile_config.name)        # "sentiment-analyzer"
print(info.encoderfile_config.model_type)  # "sequence_classification"
print(info.encoderfile_config.version)     # "1.0.0"
print(info.model_config.id2label)          # {0: "NEGATIVE", 1: "POSITIVE"}

Next Steps

Python API Reference — full documentation for every class and function
Transforms Guide — custom post-processing with Lua scripts
CLI Reference — build, serve, and infer commands for the compiled binary

encoderfile/docs/python/building-with-python.md at main · mozilla-ai/encoderfile · GitHub