dmypy

Type check a file, and start the daemon if it is not running

$ dmypy check -- [path/to/file.py]

$ dmypy start

$ dmypy run -- [path/to/file.py]

$ dmypy stop

dmypy [-h] [-V] [--config-file FILE] [--log-dir DIR] [--status-file FILE] [--wait]
{start|run|status|stop|restart|kill} [<args>]

-h, --help
    Show help message and exit.

-V, --version
    Show program's version number and exit.

--config-file FILE
    Path to mypy configuration file (mypy.ini or pyproject.toml).

--log-dir DIR
    Directory for daemon log files.

--status-file FILE
    File to store daemon status (PID, socket).

--wait
    Wait for daemon startup before exiting.

start [-- <daemon-options>]
    Start the mypy daemon server; daemon-options passed after --.

run [-- <run-options>] <files>...
    Run incremental type check on files using daemon; options after --.

status
    Print daemon status (running/PID/socket).

stop
    Gracefully stop the daemon.

restart
    Stop and immediately restart the daemon.

kill
    Force-kill the daemon process.

dmypy is the daemonized version of mypy, a static type checker for Python code. It runs a persistent server that maintains an in-memory cache of type information, enabling significantly faster incremental type checks compared to standard mypy invocations. This is ideal for large codebases, IDE integrations, or repeated checks in development workflows.

The workflow starts with dmypy start to launch the server, optionally passing mypy daemon options after --. Use dmypy run followed by files or directories to check incrementally. Other commands manage the daemon: status shows server state, stop shuts it down, restart restarts it, and kill forcefully terminates.

dmypy supports mypy configuration files and most flags, inheriting options like --strict or --python-version. It improves performance by avoiding full re-parsing and type inference on unchanged files, but requires compatible Python versions (3.7+ typically). Logs and status files aid debugging in shared or CI environments.

Daemon persists across sessions, consuming memory (~100-500MB for large projects); use stop or kill to clean up. Not compatible with all mypy plugins. Requires mypy installation. Socket files may need cleanup if crashed.

dmypy start -- --strict
dmypy run src/*.py
dmypy status
dmypy stop

Uses standard mypy config (mypy.ini or pyproject.toml). Daemon inherits settings; override with --config-file or command-line.

Introduced in mypy 0.401 (January 2017) to address performance issues in incremental checking. Developed by mypy team led by Jukka Lehtosalo; evolved with mypy releases, now at feature parity with mypy 1.x. Widely used in IDEs like VS Code via pylsp-mypy.

mypy(1), stubgen(1)