python-codex 0.1.3

A minimal Python extraction of Codex's main agent loop

pycodex

English README. Chinese version: README_ZH.md

PyPI distribution name: python-codex
Import path and CLI command remain pycodex.

This repository extracts the core Codex agent loop from upstream Codex (https://github.com/openai/codex) into a deliberately small Python version, while preserving the two most important layers:

• submission_loop: sequentially consumes submitted operations.
• run_turn: keeps executing model sample -> tool call -> feed tool result back into the model inside a single turn until a final answer is reached.

Relevant Rust reference points:

• codex-rs/core/src/codex.rs -> submission_loop
• codex-rs/core/src/codex.rs -> run_turn
• codex-rs/core/src/codex.rs -> run_sampling_request
• codex-rs/core/src/tools/router.rs -> ToolRouter
• codex-rs/core/src/stream_events_utils.rs -> handle_output_item_done

Quick Start

Install dependencies first:

uv sync

Try the real entry points:

uv run pycodex "Reply with exactly OK."
uv run pycodex

Design Tradeoffs

This is not a 1:1 port of the Rust implementation. The current goal is a minimal reusable kernel that converges on the upstream behavior over time:

1. Use a thin ModelClient protocol to abstract the model side.
2. Use ToolRegistry to manage tool specs and executors.
3. Use AgentLoop to implement the core closed loop.
4. Use AgentRuntime to preserve the outer submission queue so it can keep converging toward Rust's submission_loop later.

Intentionally not included yet:

• TUI / streaming incremental rendering
• MCP / connectors / sandbox / approvals
• memory / compact / hooks / review mode
• a full production OpenAI adapter surface

All of those can be layered on later. For now, the project is focused on nailing the core tool-augmented reasoning loop first.

Layout

• pycodex/protocol.py: minimal conversation item / prompt / event protocol
• pycodex/model.py: model client protocol and Responses API adapter
• pycodex/cli.py: single-turn and interactive pycodex CLI entry points
• pycodex/tools/base_tool.py: BaseTool, ToolRegistry, ToolContext
• pycodex/tools/: concrete tool implementations
• pycodex/agent.py: inner turn loop
• pycodex/runtime.py: outer submission queue
• tests/test_agent.py: core behavior tests

Current Alignment Status

Current progress is easiest to read in layers:

• prompt/context alignment:
  • on the non-interactive exec path, instructions and input already match upstream Codex;
  • this layer is now mainly handled by pycodex/context.py plus vendored prompt data.
• turn-loop semantic alignment:
  • AgentLoop no longer uses a fixed 12-iteration cap by default;
  • like upstream, it now converges naturally based on whether there is still follow-up work or tool handoff to do;
  • the local iteration-limit parameter is gone.
• request-level alignment:
  • the non-interactive exec request body is mostly aligned;
  • the default CLI non-exec first request now also follows the upstream codex-tui + <collaboration_mode> path;
  • the default CLI two-turn main-thread request/header behavior has also been captured and aligned, including omitting workspaces on later turns;
  • the remaining work is now more about outer behavior branches than this already-compared request/header path.
• tool round-trip alignment:
  • the Default-mode unavailable path for request_user_input is aligned to real upstream captures;
  • the Plan-mode happy path is also aligned at the tool/protocol layer based on upstream source: it forces isOther=true, requires non-empty options, and returns structured answers as a JSON string plus success=true;
  • there is now a deterministic round-trip comparison helper, tests/compare_request_user_input_roundtrip.py, built on the proxy mode in tests/fake_responses_server.py; against the locally installed codex-cli 0.115.0, the only remaining Plan-mode live-capture schema difference is that pycodex includes success=true in function_call_output.

See docs/ALIGNMENT.md for more detailed notes.

Live Model Integration

If this machine already has a Codex CLI configuration, pycodex can reuse the model, model_provider, base_url, and env_key from ~/.codex/config.toml directly:

from pycodex import ResponsesModelClient

client = ResponsesModelClient.from_codex_config()

The current implementation uses the streaming OpenAI-compatible /responses endpoint. This path has already been validated against the local ~/.codex/config.toml setup.

When launched through the CLI, pycodex also loads .env from the same configuration directory before reading config (typically ~/.codex/.env), so provider keys and similar environment variables can live there. To match upstream Codex, variables starting with CODEX_ are not imported from .env.

pycodex CLI

pycodex now defaults to a minimal interactive entry point. Internally it uses AgentRuntime to drive the turn submission loop and reuses ~/.codex/config.toml by default:

pycodex
pycodex "Summarize this repo in one sentence."
printf 'Reply with exactly OK.' | pycodex
pycodex --json "Reply with exactly OK."
pycodex --profile model_proxy "Reply with exactly OK."
pycodex --vllm-endpoint http://127.0.0.1:18000 "Reply with exactly OK."
pycodex --put @127.0.0.1:5577
pycodex --put /data/.codex/@127.0.0.1:5577
pycodex --call SECRET-CALLID@127.0.0.1:5577 "Reply with exactly OK."
pycodex doctor

Current behavior:

• with no argv prompt and a TTY stdin, enter interactive mode
• with an argv prompt or piped stdin, run a single turn
• interactive mode supports /exit and /quit
• interactive mode shows a compact event stream for user-visible phases such as tool execution and model follow-up after tool results
• assistant text is printed from streaming deltas directly
• interactive mode supports /history, /title, and /model
• /model <name> switches the model used by later turns in the current interactive session; /model shows the current model and available choices
• steer is enabled by default in interactive mode: normal input goes into the runtime steer path, the current request stops at the next safe boundary, and later steer text is appended to the next model request's input in order; for explicit queueing, use /queue <message>, which prints [steer] queued: ... and later [steer] inserted: ...
• the default built-in tool subset currently exposed as local tools is: shell, shell_command, exec_command, write_stdin, exec, wait, web_search, update_plan, request_user_input, request_permissions, spawn_agent, send_input, resume_agent, wait_agent, close_agent, apply_patch, grep_files, read_file, list_dir, view_image
• --vllm-endpoint http://host:port automatically launches a local responses_server compatibility layer; when the URL path is empty it is normalized to /v1, and /responses requests are still forwarded to the downstream /v1/chat/completions endpoint. For model_provider = "vllm", reasoning is now preserved across this path: chat chunks with reasoning or reasoning_content are translated back into Responses reasoning items, and historical reasoning items are replayed into downstream assistant messages via the reasoning field. Streaming token usage is also requested from vLLM and forwarded to the final response.completed.response.usage
• pycodex doctor checks config, .env, API keys, DNS, TCP/TLS, and an optional live Responses API request

Current primary uses:

• verify provider / model / auth configuration
• debug ResponsesModelClient
• run minimal single-turn and multi-turn smoke tests

doctor examples:

pycodex doctor
pycodex doctor --skip-live
pycodex doctor --json

Portable Mode

Portable Mode is the quickest way to bring your usual pycodex setup into a fresh machine, container, or debug image.

Use it like this:

pycodex --put @127.0.0.1:5577
pycodex --put /data/.codex/@127.0.0.1:5577

• --put prints a reusable SECRET-CALLID@host:port plus a final one-line pycodex --call ... command
• on the new environment or image, run that printed --call command directly
• quickly restoring your usual config.toml, .env, AGENTS.md, and skills/ into a clean debug environment
• keeping a new image focused on the bug you are debugging instead of spending time rebuilding local Codex setup by hand
• bootstrapping pycodex even when the target environment does not already have a populated ~/.codex
• bare --put uses the current user's ~/.codex
• --put /path/.codex/@host:port lets you publish a different Codex home

Example

import asyncio

from pycodex import (
    AgentLoop,
    BaseTool,
    ContextManager,
    ResponsesModelClient,
    ToolRegistry,
)


class EchoTool(BaseTool):
    name = "echo"
    description = "Echo the provided text."
    input_schema = {
        "type": "object",
        "properties": {"text": {"type": "string"}},
        "required": ["text"],
    }

    async def run(self, context, args):
        del context
        return args["text"]


async def main() -> None:
    model = ResponsesModelClient.from_codex_config()
    context_manager = ContextManager.from_codex_config()

    tools = ToolRegistry()
    tools.register(EchoTool())

    agent = AgentLoop(model, tools, context_manager)
    result = await agent.run_turn(
        ["Call the echo tool with text=hello, then tell me what it returned."]
    )
    print(result.output_text)


asyncio.run(main())

Alignment Checklist

See docs/ALIGNMENT.md for more detail. This section keeps a high-level checklist for quick status scanning.

Tool Alignment

Official upstream tools:

• shell - run shell commands in argv form.
• shell_command - run shell scripts in string form.
• exec_command - start long-running commands with a session.
• write_stdin - write stdin to an existing execution session or poll output.
• web_search - expose provider-native web search capability.
• update_plan - update the task plan and maintain step status.
• request_user_input - ask the user structured questions and wait for an answer.
• request_permissions - request extra permissions before continuing.
• spawn_agent - create and start a sub-agent.
• send_input - continue feeding input to an existing sub-agent.
• resume_agent - reopen a closed sub-agent.
• wait_agent - wait for a sub-agent to reach a terminal state.
• close_agent - close a sub-agent that is no longer needed.
• apply_patch - edit files precisely with a freeform patch.
• grep_files - search file contents by pattern.
• read_file - read file slices while preserving line-number semantics.
• list_dir - list directory tree slices.
• view_image - turn a local image into model-visible input.

Upstream low-frequency / special-mode tools not yet modeled separately:

• wait_infinite - long blocking wait for external events or later input.
• spawn_agents_on_csv - create sub-agent jobs in bulk from CSV.
• report_agent_job_result - report batch agent job results.
• js_repl - JavaScript REPL / code-mode primary entry point.
• js_repl_reset - reset js_repl state.
• artifacts - generate or manage structured artifact outputs.
• list_mcp_resources - list MCP resources.
• list_mcp_resource_templates - list MCP resource templates.
• read_mcp_resource - read MCP resource contents.
• multi_tool_use.parallel - parallel wrapper around multiple developer tool calls.

Repository-specific compatibility / transition tools:

• exec - current local approximation of code mode.
• wait - current local approximation of code-mode waiting behavior.

Behavior Alignment

• AgentLoop / AgentRuntime main loop skeleton - turn loop and submission queue are in place.
• non-interactive exec instructions alignment - base instructions match upstream.
• non-interactive exec input alignment - prompt input matches upstream.
• developer/contextual-user message shape alignment - message/content shape matches upstream.
• AGENTS.md + <environment_context> injection alignment - context assembly order matches upstream.
• non-interactive exec tool subset alignment - the model-visible tool set has converged.
• include = ["reasoning.encrypted_content"] - reasoning include field is aligned.
• prompt_cache_key - request-level prompt cache key is implemented.
• x-client-request-id - request id header is implemented.
• x-codex-turn-metadata - turn id / sandbox header is implemented.
• originator - mode-aware originator header is implemented.
• exact user-agent string alignment - aligned on the non-interactive exec path.
• field-by-field exec-mode tool schema alignment - currently reuses the upstream snapshot directly through the tool layer.
• full interactive-mode and non-exec behavior alignment - the non-exec first-turn context is now on the codex-tui path, but continuous REPL multi-turn behavior is not fully verified yet.
• sandbox / approvals / compact / memory and other outer behavior alignment
  • these systems are still in later scope.