martian-linguafranca 0.1.4

LLM API format converter with Rust core and Python bindings

linguafranca

LLM API format converter with a Rust core and Python bindings.

Converts requests, responses, and streaming events between:

• OpenAI Chat Completions
• Anthropic Messages
• Open Responses

Installation

# Python
pip install martian-linguafranca
# or
uv add martian-linguafranca
# Installs as 'martian-linguafranca', import as 'linguafranca'

# Rust
cargo add linguafranca

Supported formats

FormatName	API
FormatName.OPENAI_CHAT_COMPLETIONS	OpenAI Chat Completions
FormatName.ANTHROPIC_MESSAGES	Anthropic Messages
FormatName.OPEN_RESPONSES	Open Responses

Every pair is supported in both directions for requests and responses.

Quick start

import linguafranca as lf

# Convert a Chat Completions request to Anthropic Messages
result = lf.convert_request_json(
    {"model": "gpt-4.1-mini", "messages": [{"role": "user", "content": "hello"}]},
    source_format=lf.FormatName.OPENAI_CHAT_COMPLETIONS,
    target_format=lf.FormatName.ANTHROPIC_MESSAGES,
)

result.value     # converted dict
result.warnings  # list of lossy conversion warnings (dropped/modified fields)

Converting requests

import linguafranca as lf

# OpenAI Chat Completions -> Anthropic Messages
result = lf.convert_request_json(
    {
        "model": "gpt-4.1-mini",
        "messages": [{"role": "user", "content": "hello"}],
        "temperature": 0.7,
    },
    source_format=lf.FormatName.OPENAI_CHAT_COMPLETIONS,
    target_format=lf.FormatName.ANTHROPIC_MESSAGES,
)
print(result.value)
# {"model": "gpt-4.1-mini", "max_tokens": 4096, "messages": [...], ...}

# Anthropic Messages -> OpenAI Chat Completions
result = lf.convert_request_json(
    {
        "model": "claude-3-5-sonnet",
        "max_tokens": 64,
        "messages": [{"role": "user", "content": "hello"}],
    },
    source_format=lf.FormatName.ANTHROPIC_MESSAGES,
    target_format=lf.FormatName.OPENAI_CHAT_COMPLETIONS,
)

Convenience wrappers

When you always target the same format, convenience wrappers save some typing:

# Convert anything -> Anthropic Messages
result = lf.to_messages_request(
    openai_request,
    source_format=lf.FormatName.OPENAI_CHAT_COMPLETIONS,
)

# Convert anything -> OpenAI Chat Completions
result = lf.to_chat_completions_request(
    anthropic_request,
    source_format=lf.FormatName.ANTHROPIC_MESSAGES,
)

The same pattern works for responses with to_messages_response and to_chat_completions_response.

Converting responses

result = lf.convert_response_json(
    {
        "id": "chatcmpl-abc123",
        "object": "chat.completion",
        "model": "gpt-4.1-mini",
        "choices": [{
            "index": 0,
            "message": {"role": "assistant", "content": "Hello!"},
            "finish_reason": "stop",
        }],
        "usage": {"prompt_tokens": 5, "completion_tokens": 7, "total_tokens": 12},
    },
    source_format=lf.FormatName.OPENAI_CHAT_COMPLETIONS,
    target_format=lf.FormatName.ANTHROPIC_MESSAGES,
)
print(result.value)

Streaming

Sync streaming with httpx

import json
import httpx
import linguafranca as lf

def parse_sse(response: httpx.Response):
    """Yield parsed JSON objects from an SSE stream."""
    for line in response.iter_lines():
        if line.startswith("data: ") and line != "data: [DONE]":
            yield json.loads(line[6:])

headers = {"Authorization": "Bearer YOUR_KEY", "Content-Type": "application/json"}
payload = {
    "model": "gpt-4.1-mini",
    "messages": [{"role": "user", "content": "hello"}],
    "stream": True,
}

with httpx.stream("POST", "https://api.openai.com/v1/chat/completions",
                   headers=headers, json=payload) as resp:
    stream = lf.convert_response_stream_json(
        parse_sse(resp),
        source_format=lf.FormatName.OPENAI_CHAT_COMPLETIONS,
        target_format=lf.FormatName.OPEN_RESPONSES,
    )
    for event in stream:
        print(event)

    # Check warnings after the stream is fully consumed
    for w in stream.take_warnings():
        print(f"{w.field}: {w.message}")

Async streaming with httpx

import json
import httpx
import linguafranca as lf

async def parse_sse(response: httpx.Response):
    async for line in response.aiter_lines():
        if line.startswith("data: ") and line != "data: [DONE]":
            yield json.loads(line[6:])

async def main():
    headers = {"Authorization": "Bearer YOUR_KEY", "Content-Type": "application/json"}
    payload = {
        "model": "gpt-4.1-mini",
        "messages": [{"role": "user", "content": "hello"}],
        "stream": True,
    }

    async with httpx.AsyncClient() as client:
        async with client.stream("POST",
                                 "https://api.openai.com/v1/chat/completions",
                                 headers=headers, json=payload) as resp:
            stream = lf.aconvert_response_stream(
                parse_sse(resp),
                source_format=lf.FormatName.OPENAI_CHAT_COMPLETIONS,
                target_format=lf.FormatName.OPEN_RESPONSES,
            )
            async for event in stream:
                print(event)

Typed payloads (recommended)

The package ships auto-generated @dataclass definitions for all three formats via linguafranca.types. Using them gives you IDE autocompletion, type checking, and catches mistakes before the payload hits the converter.

import linguafranca as lf
from linguafranca.types import (
    ChatCompletionsOpenAiRequest,
    ChatCompletionsMessageUser,
)

request = ChatCompletionsOpenAiRequest(
    model="gpt-4.1-mini",
    messages=[
        ChatCompletionsMessageUser(content="hello", role="user"),
    ],
    temperature=0.7,
)

result = lf.convert_request(
    request,
    source_format=lf.FormatName.OPENAI_CHAT_COMPLETIONS,
    target_format=lf.FormatName.ANTHROPIC_MESSAGES,
)
print(result.value)

The non-_json variants (convert_request, convert_response, convert_response_stream) accept any of:

• linguafranca.types dataclasses (recommended)
• plain dicts
• Pydantic models — serialised via model.model_dump()

The _json variants (convert_request_json, convert_response_json, convert_response_stream_json) accept and return plain dicts only.

Warnings

Conversions between formats can be lossy — some fields exist in one format but not another. When this happens, the library returns warnings instead of failing:

result = lf.convert_request_json(
    request,
    source_format=lf.FormatName.OPENAI_CHAT_COMPLETIONS,
    target_format=lf.FormatName.ANTHROPIC_MESSAGES,
)

for w in result.warnings:
    print(f"{w.field}: {w.message}")
    # e.g. "frequency_penalty: field not supported in Anthropic Messages, dropped"

For streaming, call stream.take_warnings() after the stream is consumed.

Error handling

All errors inherit from ConversionError:

import linguafranca as lf

# Invalid payload structure
try:
    lf.convert_request_json(
        {"not": "a valid request"},
        source_format=lf.FormatName.OPENAI_CHAT_COMPLETIONS,
        target_format=lf.FormatName.ANTHROPIC_MESSAGES,
    )
except lf.SchemaValidationError as e:
    print(e)  # payload doesn't match the source format schema

# Unsupported conversion pair (streaming only)
try:
    lf.convert_response_stream_json(
        events,
        source_format=lf.FormatName.OPEN_RESPONSES,
        target_format=lf.FormatName.OPEN_RESPONSES,
    )
except lf.UnsupportedConversionError as e:
    print(e)

All available types

All request, response, and streaming event types for each format are available under linguafranca.types:

from linguafranca.types import (
    # OpenAI Chat Completions
    ChatCompletionsOpenAiRequest,
    ChatCompletionsMessageUser,
    ChatCompletionsMessageSystem,
    ChatCompletionsMessageAssistant,
    ChatCompletionsResponse,
    ChatCompletionsStreamChunk,
    # Anthropic Messages
    AnthropicRequest,
    AnthropicMessage,
    AnthropicResponse,
    # Open Responses
    OpenResponsesRequest,
    OpenResponsesResponse,
    # ... and all nested types (content parts, tool calls, etc.)
)

These are standard @dataclass definitions generated from the Rust schemas. See Typed payloads for usage examples.

License

MIT