py-llmify 0.8.0

A minimal, fast, and type-safe Python library for LLM chat completions across multiple providers

llmify

A lightweight, type-safe Python library for LLM chat completions.

Features:

• Simple, intuitive API for OpenAI, Codex, Azure OpenAI, Cerebras, Anthropic, and Google Gemini
• Type-safe structured outputs with Pydantic
• Built-in tool calling support
• Async streaming
• Image analysis support
• Optional token usage and cost tracking
• Minimal dependencies, maximum flexibility

Installation

pip install py-llmify

Install only the provider you need:

pip install py-llmify[openai]      # OpenAI + Azure OpenAI
pip install py-llmify[cerebras]    # Cerebras
pip install py-llmify[anthropic]   # Anthropic (Claude)
pip install py-llmify[google]      # Google Gemini
pip install py-llmify[all]         # All providers
pip install py-llmify[tokens]      # Token tracking + Tokenary cost calculation

The tokens extra currently requires Python 3.13 because that is the minimum Python version supported by Tokenary. Extras can be combined, for example:

pip install py-llmify[openai,tokens]

Quick Start

import asyncio
from llmify import ChatOpenAI, UserMessage, SystemMessage

async def main():
    llm = ChatOpenAI(model="gpt-4o")

    response = await llm.invoke([
        SystemMessage(content="You are a helpful assistant"),
        UserMessage(content="What is 2+2?")
    ])

    print(response.completion)  # "2+2 equals 4"

asyncio.run(main())

All invoke calls return a ChatInvokeCompletion[T] with:

• completion — the text (or parsed Pydantic model) returned by the model
• tool_calls — list of ToolCall objects, if any
• usage — token usage (ChatInvokeUsage)
• stop_reason — why the model stopped

Core Features

Message Types

from llmify import SystemMessage, UserMessage, AssistantMessage, ToolResultMessage

messages = [
    SystemMessage(content="You are a Python expert"),
    UserMessage(content="How do I read a file?"),
    AssistantMessage(content="You can use open() with a context manager"),
    UserMessage(content="Show me an example"),
]

Image messages

Pass images inline inside a UserMessage using content parts:

from llmify import UserMessage, ContentPartTextParam, ContentPartImageParam, ImageURL

message = UserMessage(
    content=[
        ContentPartTextParam(text="What's in this image?"),
        ContentPartImageParam(
            image_url=ImageURL(
                url="data:image/jpeg;base64,<base64data>",
                media_type="image/jpeg",
                detail="high",
            )
        ),
    ]
)

Structured Outputs

Pass output_format to get a validated Pydantic model back:

from pydantic import BaseModel
from llmify import ChatOpenAI, UserMessage

class Person(BaseModel):
    name: str
    age: int
    occupation: str

async def main():
    llm = ChatOpenAI(model="gpt-4o")

    response = await llm.invoke(
        [UserMessage(content="Extract: John is 32 and works as a data scientist")],
        output_format=Person,
    )

    person = response.completion  # type: Person
    print(f"{person.name}, {person.age}, {person.occupation}")
    # John, 32, data scientist

asyncio.run(main())

Tool Calling

@tool decorator

Define tools from plain Python functions:

import json
from llmify import ChatOpenAI, UserMessage, AssistantMessage, ToolResultMessage, tool

@tool
def get_weather(location: str, unit: str = "celsius") -> str:
    """Get current weather for a location"""
    return f"Weather in {location}: 22°{unit[0].upper()}, Sunny"

async def main():
    llm = ChatOpenAI(model="gpt-4o")
    messages = [UserMessage(content="What's the weather in Paris?")]

    response = await llm.invoke(messages, tools=[get_weather])

    if response.tool_calls:
        tc = response.tool_calls[0]
        args = json.loads(tc.function.arguments)
        result = get_weather(**args)

        messages.append(AssistantMessage(content=response.completion, tool_calls=response.tool_calls))
        messages.append(ToolResultMessage(tool_call_id=tc.id, content=result))

        final = await llm.invoke(messages)
        print(final.completion)

asyncio.run(main())

RawSchemaTool

Use a raw JSON schema when you need full control over the tool definition:

import json
from llmify import ChatOpenAI, UserMessage, AssistantMessage, ToolResultMessage, RawSchemaTool

search_tool = RawSchemaTool(
    name="search_web",
    description="Search the web for information",
    schema={
        "type": "object",
        "properties": {
            "query": {"type": "string", "description": "Search query"},
            "max_results": {"type": "integer", "default": 5},
        },
        "required": ["query"],
    },
)

async def main():
    llm = ChatOpenAI(model="gpt-4o-mini")
    messages = [UserMessage(content="Search for Python 3.13 features")]

    response = await llm.invoke(messages, tools=[search_tool])

    if response.tool_calls:
        tc = response.tool_calls[0]
        args = json.loads(tc.function.arguments)
        result = my_search_fn(**args)

        messages.append(AssistantMessage(content=response.completion, tool_calls=response.tool_calls))
        messages.append(ToolResultMessage(tool_call_id=tc.id, content=result))

        final = await llm.invoke(messages)
        print(final.completion)

asyncio.run(main())

Dict schema

Pass raw OpenAI-style tool dicts directly:

tools = [
    {
        "type": "function",
        "function": {
            "name": "get_weather",
            "description": "Get the current weather",
            "parameters": {
                "type": "object",
                "properties": {
                    "city": {"type": "string"},
                },
                "required": ["city"],
            },
        },
    }
]

response = await llm.invoke(messages, tools=tools)
print(response.tool_calls[0].function.name)
print(json.loads(response.tool_calls[0].function.arguments))

Streaming

import json
from llmify import ChatOpenAI, UserMessage, StreamEventType

async def main():
    llm = ChatOpenAI()
    chunk_count = 0

    async for event in llm.stream([UserMessage(content="Write a haiku about Python")]):
        if event.type is StreamEventType.TEXT:
            chunk_count += 1
            print(f"[{chunk_count:02d}]{event.delta}", end="", flush=True)
        elif event.type is StreamEventType.END:
            print(f"\n[stream_end stop={event.stop_reason}]")

asyncio.run(main())

For streaming with tools, handle StreamEventType.TOOL_CALL and parse the complete JSON arguments:

import json
from llmify import ChatOpenAI, UserMessage, StreamEventType

async def main():
    llm = ChatOpenAI()

    async for event in llm.stream(messages, tools=[get_weather]):
        if event.type is StreamEventType.TEXT:
            print(event.delta, end="", flush=True)
        elif event.type is StreamEventType.TOOL_CALL:
            args = json.loads(event.tool_call.function.arguments)
            result = get_weather(**args)
            print(f"\n[tool_result] {result}")
        elif event.type is StreamEventType.END:
            print(f"\n[stream_end stop={event.stop_reason} tokens={event.usage.total_tokens if event.usage else 'unknown'}]")

asyncio.run(main())

Full runnable example: examples/streaming_tool_calls.py

Token Usage Tracking

Every provider exposes the model it talks to via the required .model property:

llm = ChatOpenAI(model="gpt-4o")
print(llm.model)  # "gpt-4o"

Token tracking is an optional feature. Install py-llmify[tokens], then create a TokenTracker and feed it the usage you care about. Its add method accepts a ChatInvokeUsage, a full ChatInvokeCompletion, or a StreamEnd event, together with the model name (conveniently available as llm.model). The same tracker can aggregate usage and Tokenary-backed USD costs across many calls and models:

from llmify import ChatOpenAI, ChatAnthropic, UserMessage
from llmify.tokens import ModelName, TokenTracker, calculate_cost, calculate_costs

tracker = TokenTracker()
gpt_model = ModelName.GPT_4O
claude_model = ModelName.CLAUDE_SONNET_4_20250514
gpt = ChatOpenAI(model=gpt_model)
claude = ChatAnthropic(model=claude_model)

# Pass the completion object directly...
r1 = await gpt.invoke([UserMessage(content="Hi")])
tracker.add(r1, model=gpt_model)

r2 = await gpt.invoke([UserMessage(content="How are you?")])
tracker.add(r2, model=gpt_model)

# ...or a StreamEnd event (or a raw ChatInvokeUsage).
async for event in claude.stream([UserMessage(content="Hi")]):
    if event.type == "end":
        tracker.add(event, model=claude_model)

summary = tracker.summary()     # UsageSummary across both providers
print(summary.entry_count)              # 3
print(summary.total_tokens)             # e.g. 84
print(summary.total_prompt_tokens)
print(summary.total_completion_tokens)
print(summary.total_prompt_cached_tokens)

cost = calculate_cost(r1, model=gpt_model)  # Tokenary CostBreakdown
print(cost.total_cost)

# Aggregate an existing same-model chain without building a tracker.
chain_cost = calculate_costs([r1, r2], model=gpt_model)
print(chain_cost.total_cost)

# A tracker also supports multi-model chains because every entry is tagged.
cost_summary = tracker.cost_summary()
print(cost_summary.currency)                # "USD"
print(cost_summary.total_cost)
print(tracker.costs())                      # per-call Tokenary CostBreakdown list

print(tracker.entries)          # per-call TokenUsageEntry list (each tagged with `model`)
tracker.reset()                 # start a fresh accounting window

Cost calculation uses Tokenary's bundled model catalog. An unknown model raises KeyError; missing usage raises ValueError.

Full runnable example: examples/token_tracking.py

Configuration

Environment Variables

# OpenAI
export OPENAI_API_KEY="sk-..."

# Codex
export CODEX_ACCESS_KEY="..."
export CODEX_ACCOUNT_ID="..."

# Azure OpenAI
export AZURE_OPENAI_API_KEY="..."
export AZURE_OPENAI_ENDPOINT="https://<resource>.openai.azure.com/"

# Cerebras
export CEREBRAS_API_KEY="csk-..."

# Anthropic
export ANTHROPIC_API_KEY="sk-ant-..."

# Google Gemini
export GEMINI_API_KEY="..."

Model Parameters

Set defaults when initializing or override per request:

llm = ChatOpenAI(
    model="gpt-4o",
    temperature=0.7,
    max_tokens=1000,
)

response = await llm.invoke(
    messages=[UserMessage(content="Hi")],
    temperature=0.2,
    max_tokens=500,
)

Supported parameters: temperature, max_tokens, top_p, frequency_penalty, presence_penalty, stop, seed.

Providers

OpenAI

from llmify import ChatOpenAI

llm = ChatOpenAI(
    model="gpt-4o",
    api_key="sk-...",  # optional if OPENAI_API_KEY is set
    base_url="https://...",  # optional, defaults to the OpenAI API
    default_headers={"X-My-Header": "value"},  # optional
)

api_key also accepts an async callable (() -> str), which is awaited before every request — useful for short-lived tokens that need refreshing.

OpenAI Responses API

from llmify import ChatOpenAIResponses

llm = ChatOpenAIResponses(
    model="gpt-5.4-mini",
    api_key="sk-...",  # optional if OPENAI_API_KEY is set
    base_url="https://...",  # optional, defaults to the OpenAI API
)

Use ChatOpenAIResponses when an endpoint exposes OpenAI's Responses API rather than the Chat Completions API. It supports the same llmify invoke and stream interface.

Codex

from llmify import ChatCodex

llm = ChatCodex(
    model="gpt-5.6-terra",
    api_key="...",  # optional if CODEX_ACCESS_KEY is set
    chatgpt_account_id="...",
)

ChatCodex specializes ChatOpenAIResponses for the Codex endpoint and configures the required ChatGPT-Account-Id header from chatgpt_account_id. The endpoint URL is fixed by the provider and does not need to be supplied by callers.

This is a reverse-engineered endpoint: it authenticates with a ChatGPT subscription rather than an API key, and OpenAI does not document or support it.

Borrowing the Codex CLI login

If the Codex CLI is installed and logged in (codex login), its session can be used directly — no environment variables:

llm = ChatCodex.from_codex_cli(model="gpt-5.6-terra")

This reads ~/.codex/auth.json (or $CODEX_HOME/auth.json) for the account id and access token — no network access, no writes. From the request path onwards the token is refreshed as it approaches expiry, and the rotated tokens are written back so the CLI keeps working. The approach is borrowed from llm-openai-via-codex.

For the credentials themselves, a different auth.json, or one token provider shared across several clients, compose the two pieces yourself:

from llmify import ChatCodex, CodexCliAuth
from llmify.auth import read_codex_credentials

credentials = read_codex_credentials()  # or read_codex_credentials(auth_path=...)
print(credentials.expires_in)           # seconds until the access token expires

auth = CodexCliAuth(credentials)
llm = ChatCodex(
    model="gpt-5.6-terra",
    api_key=auth,                       # awaited before every request
    chatgpt_account_id=auth.account_id,
)

read_codex_credentials() only ever reads the file. Its async counterpart refresh_codex_credentials() is what performs the OAuth refresh and the write-back — CodexCliAuth calls it from the request path when the token is about to expire, and applications that want to control that themselves can call it directly.

A missing or unusable login raises CodexCredentialsError, a subclass of CredentialsUnavailableError.

Full runnable examples: examples/providers/borrowed_codex.py and examples/providers/codex_cli_auth.py

Azure OpenAI

from llmify import ChatAzureOpenAI

llm = ChatAzureOpenAI(
    model="gpt-4o",
    api_key="...",           # optional if AZURE_OPENAI_API_KEY is set
    azure_endpoint="https://<resource>.openai.azure.com/",  # optional if env var is set
)

Anthropic

from llmify import ChatAnthropic

llm = ChatAnthropic(
    model="claude-sonnet-4-20250514",
    api_key="sk-ant-...",  # optional if ANTHROPIC_API_KEY is set
)

The Anthropic provider supports the same API surface — invoke, stream, structured output, and tool calling — all mapped to the Anthropic messages API under the hood.

Cerebras

from llmify import ChatCerebras

llm = ChatCerebras(
    model="gpt-oss-120b",
    api_key="csk-...",  # optional if CEREBRAS_API_KEY is set
)

The Cerebras provider uses Cerebras' OpenAI-compatible API and supports invoke, stream, structured output, and tool calling.

Google Gemini

from llmify import ChatGoogle

llm = ChatGoogle(
    model="gemini-3.5-flash",
    api_key="...",  # optional if GEMINI_API_KEY is set
)

The Google provider supports the same API surface: invoke, stream, structured output, and tool calling.

Credits

Inspired by LangChain and browser-use.

License

MIT