basedpyright 1.2.0

static type checking for Python (but based)

basedpyright

Basedpyright is a static type checker for Python that is built on top of the work done by the pyright project.

why?

pyright has several serious limitations which were the main motivation behind this fork.

pyright has no way to pin the version used by vscode

this means if the extension gets updated, you may see errors in your project that don't appear in the CI, or vice-versa. see this issue

no way to run the pyright CLI without nodejs

python developers should not be expected to have to install nodejs in order to typecheck their python code. it should just be a regular pypi package, just like mypy, ruff, and pretty much every other python command line tool

issues with unreachable code

pyright often incorrectly marks code as unreachable. in most cases, unreachable code is a mistake and therefore should be an error, but pyright does not have an option to report unreachable code. in fact, unreachable code is not even type-checked at all:

if sys.platform == "win32": 
  1 + "" # no error

by default, pyright will treat the body in the code above as unreachable if pyright itself was run on an operating system other than windows. this is bad of course, because chances are if you write such a check, you intend for your code to be executed on multiple platforms.

to make things worse, unreachable code is not even type-checked, so the obviously invalid 1 + "" above will go completely unnoticed by the type checker.

basedpyright solves this issue with a reportUnreachable option, which will report an error on such unchecked code. in this example, you can update your pyright config to specify more platforms using the pythonPlatform option if you intend for the code to be reachable.

no errors on invalid configuration

in pyright, if you have any invalid config, it may or may not print a warning to the console, then it will continue type-checking and the exit code will be 0 as long as there were no type errors:

[tool.pyright]
mode = "strict"  # wrong! the setting you're looking for is called `typeCheckingMode`

in this example, it's very easy for errors to go undetected because you thought you were on strict mode, but in reality pyright just ignored the setting and silently continued type-checking on "basic" mode.

to solve this problem, basedpyright will exit with code 3 on any invalid config.

no way to fully ban the Any type

pyright has a few options to ban "Unknown" types such as reportUnknownVariableType, reportUnknownParameterType, etc. but "Unknown" is not a real type, rather a distinction pyright uses used to represent Anys that come from untyped code or unfollowed imports. if you want to ban all kinds of Any, pyright has no way to do that:

def foo(bar, baz: Any) -> Any:
    print(bar) # error: unknown type
    print(baz) # no error

basedpyright introduces the reportAny option, which will report an error on usages of anything typed as Any.

basedmypy feature parity

basedmypy is a fork of mypy with a similar goal in mind: to fix some of the serious problems in mypy that do not seem to be a priority for the maintainers. it also adds many new features which may not be standardized but greatly improve the developer experience when working with python's far-from-perfect type system.

we aim to port most of basedmypy's features to basedpyright, however as mentioned above our priority is to first fix the critical problems with pyright.

pypi package

basedpyright differs from pyright by publishing the command line tool as a pypi package instead of an npm package. this makes it far more convenient for python developers to use.

> basedpyright --help
Usage: basedpyright [options] files...
  Options:
  --createstub <IMPORT>              Create type stub file(s) for import
  --dependencies                     Emit import dependency information
  -h,--help                          Show this help message
  --ignoreexternal                   Ignore external imports for --verifytypes
  --level <LEVEL>                    Minimum diagnostic level (error or warning)
  --outputjson                       Output results in JSON format
  -p,--project <FILE OR DIRECTORY>   Use the configuration file at this location
  --pythonplatform <PLATFORM>        Analyze for a specific platform (Darwin, Linux, Windows)
  --pythonpath <FILE>                Path to the Python interpreter
  --pythonversion <VERSION>          Analyze for a specific version (3.3, 3.4, etc.)
  --skipunannotated                  Skip analysis of functions with no type annotations
  --stats                            Print detailed performance stats
  -t,--typeshedpath <DIRECTORY>      Use typeshed type stubs at this location
  -v,--venvpath <DIRECTORY>          Directory that contains virtual environments
  --verbose                          Emit verbose diagnostics
  --verifytypes <PACKAGE>            Verify type completeness of a py.typed package
  --version                          Print Pyright version and exit
  --warnings                         Use exit code of 1 if warnings are reported
  -w,--watch                         Continue to run and watch for changes
  -                                  Read files from stdin

vscode extension

install

install the extension from the vscode extension marketplace

usage

the basedpyright vscode extension will automatically look for the pypi package in your python environment. see the recommended setup section below for more information

pylance vs basedpyright

the pylance extension is an optional wrapper on top of the pyright language server with some additional functionality (see the pylance FAQ for more information). normally when the pylance extension is enabled, the pyright extension will disable itself to avoid conflicting with it. unfortunately since it's closed-source, there's no way for us to update it to use basedpyright instead.

if you don't depend on any pylance features, the recommended solution is to disable/uninstall the pylance extension.

if you do want to continue using pylance, all of the options and commands in basedpyright have been renamed to avoid any conflicts with the pylance extension, and the restriction that prevents both extensions from being enabled at the same time has been removed. for an optimal experience you should disable pylance's type checking and disable basedpyright's language server features. see the recommended setup section below for details.

recommended setup

it's recommended to use both the basedpyright cli and vscode extension in your project. the vscode extension is for local development and the cli is for your CI.

below are the changes i recommend making to your project when adopting basedpyright

.vscode/extensions.json

{
  "recommendations": [
    "detachhead.basedpyright" // this will prompt developers working on your project to install the extension
  ],
  "unwantedRecommendations": [
    "ms-python.vscode-pylance" // if not using pylance (see below)
  ]
}

.vscode/settings.json

if not using pylance

• remove any settings starting with python.analysis, as they are not used by basedpyright. you should instead set these settings using the tool.basedpyright (or tool.pyright) section in pyroject.toml (see below)
• disable the built in language server support from the python extension, as it seems to conflict with basedpyright's language server:

  {
      "python.languageServer": "None"
  }
  

if using pylance

• disable pylance's type-checking by setting "python.analysis.typeCheckingMode" to "off". this will prevent pylance from displaying duplicated errors from its bundled pyright version alongside the errors already displayed by the basedpyright extension.
• disable basedpyright's LSP features by setting "basedpyright.disableLanguageServices" to true. this will prevent duplicated hover text and other potential issues with pylance's LSP. keep in mind that this may result in some inconsistent behavior since pylance uses its own version of the pyright LSP.

{
    "python.analysis.typeCheckingMode": "off",
    "basedpyright.disableLanguageServices": true
}

.github/workflows/check.yaml

jobs:
  check:
    steps:
      - run: ...  # checkout repo, install dependencies, etc
      - run: basedpyright  # add this line

pyproject.toml

we recommend using pdm or poetry to manage your dependencies.

[tool.pdm.dev-dependencies]  # or the poetry equivalent
dev = [
    "basedpyright", # you can pin the version here if you want, or just rely on the lockfile
]

[tool.basedpyright]
# many settings are not enabled even in strict mode, which is why basedpyright includes an "all" option
# you can then decide which rules you want to disable
typeCheckingMode = "all"

pinning your dependencies is important because it allows your CI builds to be reproducible (ie. two runs on the same commit will always produce the same result). basedpyright ensures that the version of pyright used by vscode always matches this pinned version