Migrating from Mypy

Running Pyrefly

Like mypy, pyrefly can be given a list of files to check:

$ pyrefly check file1.py file2.py

The easiest way to run pyrefly on all files in a project is to run it from the project root:

$ cd your/project
$ pyrefly check

Pyrefly is designed to have sensible defaults, and you may not need to configure it at all. However, projects with existing mypy configs may want to configure pyrefly to suit their own needs.

Mypy Config Migration

To make it as easy as possible to get started with pyrefly, we've provided a script for automatically migrating a mypy config to pyrefly.

$ pyrefly config-migration path/to/your/mypy.ini

This will load your existing mypy.ini and transform it into a pyrefly.toml while preserving as many options as possible. See config-migration --help for more options.

We do recommend checking the resulting config for errors. While there is some overlap between mypy's config options and pyrefly's config options, it's not always possible to cleanly translate one config option to another.

If you'd rather start fresh with a hand-written config, please see the pyrefly configuration docs. If you run into any issues with config migration, please let us know!

Config Migration Details

files, modules, and packages are combined into project_includes. This should work exactly the same for files and packages. Mypy doesn't recurse into modules, but pyrefly will.

Pyrefly makes an effort to transform the exclude regex into a list of filepath globs for project_excludes. This should excel on simple regexes, such as some/file.py|exclude_dir/, which becomes ["**/some/file.py", "**/exclude_dir/"].

The ignore_missing_imports per-module config option is turned into a list of modules. For example:

[mypy-some.*.module]
ignore_missing_imports = True

Becomes:

replace_imports_with_any = ["some.*.module"]

Pyrefly does support mypy's module name pattern syntax.

Mypy's follow_untyped_imports option is allowed to be global or per-module. The pyrefly equivalent, use_untyped_imports, is only global. If any per-module section in the mypy config has follow_untyped_imports = True, then use_untyped_imports will be true in the pyrefly config.

Silencing Errors

Like mypy, pyrefly has ways to silence specific error codes. Full details can be found in the Error Suppression docs

To silence an error on a specific line, add a disable comment above that line:

# pyrefly: ignore
x: str = 1

To suppress all instances of an error, disable that error in the config:

[errors]
import-error = false

This is equivalent to mypy's disable_error_code, though of course the error codes are different!