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Pyre can be run without a configuration (see Command Line Arguments) but we do recommend that you create a configuration (see Getting Started) and commit that to your version control system to make sure everyone working on your project is using the same settings.

The Pyre Configuration​

The Pyre configuration is a .pyre_configuration file sitting at the root of your project. Running Pyre anywhere inside your project directory will use the settings in this configuration. You can generate an initial configuration in your project directory with

$ pyre init

The configuration is a JSON file. For example,

"source_directories": [
"search_path": [
{"site-package": "foo"}

specifies that the code Pyre checks is in the directory of the configuration and that Pyre should look in an additional directory as well as the foo package installed in your environment for library code.

You specify additional information to configure Pyre. The following fields are supported:

  • source_directories: List of paths to type check. Paths can be a glob, for example, "./foo*".

    Note: Pyre assumes that all imports are relative to the given source directory. For example, if your source directory is root/directory, then an import statement import module will be looking to import If you wish to set a different import root for your source directory, you can provide an object {"import_root": "root", "source": "directory"} instead of "root/directory". In this case, import module will be looking to import root.module.

  • search_path: List of paths to Python modules to include in the typing environment. Relative paths are the best way to reference locations above the configuration directory. search_path elements take precendence over source_directories, and the order within the search path indicates precedence. Individual items in the list can take one of the following forms:

    • A plain string, representing a path to the directories from which Pyre will search for modules. The paths can be globs, for example, "./foo*".
    • An object {"import_root": "root", "source": "directory"}, which can be used to control import root of the search path. See explaination for source_directories.
    • An object {"site-package": "package_name"}. It is equivalent to {"import_root": "site_root", "source": "package_name"}, where site_root is the first element in site_roots that has the site package named package_name installed. This can be useful when you want to manually specify which pip package you want the type checker to see as a dependency to your project (in which case it is recommended to set site_package_search_strategy to "none" to disable site package auto discovery).
    • An object {"site-package": "package_name", "is_toplevel_module": true}, to specify the name as a single-file module found in the site-root rather than as a package.
  • binary: Location of Pyre's native binary.

  • exclude: List of regular expressions such as ".*\/node_modules\/.*" which specify files and directories that should be completely ignored by Pyre. The regular expression will be matched against the full path of files as opposed to their relative path.

  • extensions: Consider extensions in this list equivalent to .py for type checking. Empty string indicates extensionless files.

  • ignore_all_errors: A list of paths to omit from type-checking. This may be useful for generated files, virtualenv directories, etc. These should be paths relative to the location of the configuration file and support globs. Note: Files matching these paths will still be processed (i.e. type and module names in those files are still visible to Pyre). Please refer to the exclude configuration item if you have files that are intended to be hidden from Pyre.

  • logger: Pyre will invoke this exectuable on every run, passing it statistics in JSON format.

  • site_package_search_strategy: Configure how Pyre looks for type checking dependencies installed (e.g. by pip) on the local Python environment. Dependent libraries will not be type-checked, but they are consulted to determine the existence of globals/functions/classes. The value of this option can take one of the following forms:

    • "none". This indicates that Pyre should not attempt to search for any additional dependencies. Use this option if you know exactly what packages you depend on, and want to manually specify them with the search_path option.
    • "all". Pyre will pull in the entire site package roots (as specified in the site_roots option) as dependencies. Any libraries installed as site packages, regardless of whether they are typed or not, will be examined. Use this option if you do not know exactly which packages your code depend on, but want to make sure that no dependencies are missing.
    • "pep561". Similar to "all" but instead of pull in everything, Pyre will only pull in typed packages as dependencies according to rules specified in PEP 561. This is usually the recommended option, as the behavior is closer to what other type checkers would do by default.

    Note: If incremental check is used, and the search strategy is set to "pep561", then a pyre restart is needed when new dependencies are installed -- Pyre will not automatically discover the new package by default. This is a limitation of the current implementation of Pyre and it may be lifted in the future.

  • site_roots: List of path to where packages are installed.

    If not specified, Pyre will consult the current Python interpreter using site.getusersitepackages() and site.getsitepackages(), which should work in most cases. But if your codebase uses a different Python interpreter, you may want to specify this option manually so Pyre knows the correct location to look for site packages.

  • typeshed: Path to the Typeshed standard library, which provides typed stubs for library functions.

  • workers: Number of workers to spawn for multiprocessing.

  • strict: Setting this to true will make strict mode the default in your project.

  • python_version: This is expected to be a string of the form "X.Y.Z" which specifies what version of Python the checked code is expected to be executed with. By default, the version is set to the same as the Python interpreter that runs pyre itself.

Note: Since Pyre does not run your code, the setting of Python version tends to have relatively small impact on the type checker's behavior. Currently, Pyre only uses Python version to syntactically resolve version conditions of certain form.

Command Line Arguments​

You can get a full and current list of options to run Pyre by running pyre --help. The following is a list of commonly used commands and options.


Pyre comes with a couple commands that can be invoked with pyre <COMMAND>.

The first command you might come in contact with is

  • initialize, init: Initial setup of a configuration for a project.

If Watchman is installed, running Pyre with no positional arguments defaults to incremental, otherwise defaults to check.

  • check: Run Pyre end-to-end, i.e. not incrementally.
  • incremental: Run Pyre incrementally. When invoked for the first time, the command will automatically start a server listening to changes to the filesystem. Subsequent invocations will be faster.

When Pyre is run incrementally, you can control the Pyre's server working in the background with the following commands.

  • start: Start the Pyre server.
  • stop: Stop the Pyre server.
  • restart: Restart the Pyre server.
  • servers: List all currently running Pyre servers.
  • kill: In case somethign goes wrong and the server becomes unresponsivbe kill will attempt to terminate any processes.
  • rage: Print server logs for debugging or for context when reporting server errors.

Commonly Used Flags​

These flags can be passed in before any of the positional arguments above. For example:

$ pyre --source-directory "." --noninteractive check
$ pyre --source-directory "." restart
  • --noninteractive: Disable interactive logging, which by default overwrites intermediate logging output and adds colors for a more streamlined user experience. Non-interactive mode ensures all terminal output remains visible.

  • --output {text, json, sarif}: Formatting for error return values. Defaults to text.

  • --search-path SEARCH_PATH: Provide additional stubs or modules external to the project being type-checked. Can also be set in .pyre_configuration.

  • --source-directory SOURCE_DIRECTORY: Provide a path to the source root to check. This can also be specified in .pyre_configuration.

  • --typeshed TYPESHED: Path to the Typeshed standard library, which provides typed stubs for library functions. This can also be set in .pyre_configuration.

  • --version: Print the current version of Pyre.

Helper Commands​

Working with Multi-Project Repositories​

If you have a single repository with multiple independent Python projects, we recommend you use a separate .pyre_configuration for each one. This allows each project to be type checked independently.

If you use virtual environments to manage separate dependencies for each project, you can install pyre as a development dependency in each one; by default Pyre will detect system packages from the environment it is installed in, so this will cause each project to detect the correct dependencies (assuming you activate the virtual environment before running Pyre).