Coming from mypy or pyright
This guide helps you migrate a project from mypy or pyright to ty.
Migration tips
- mypy disables an error code with
# type: ignore[code]; pyright suppresses a single line with# pyright: ignore[reportXyz]; ty's equivalent is# ty: ignore[rule]. See this page for more information about suppression comments. - mypy's
disable_error_codeand pyright'sreportXyz = "none"both correspond to setting<rule> = "ignore"under[tool.ty.rules]. See this section for details. - Severities in ty are
ignore,warn,error. Pyright's"information"level and basedpyright's"hint"level have no direct ty equivalent — usewarnfor both. - If you are looking for the equivalent of
disallow_untyped_defs/no-untyped-def(mypy) orreportMissingParameterType,reportUnknownParameterType(pyright), check out this FAQ entry. - Unlike mypy, ty checks the bodies of unannotated functions unconditionally, so there is no ty rule
corresponding to mypy's
check_untyped_defssetting. The equivalent pyright setting isanalyzeUnannotatedFunctions = true.
Stricter checking with ty
For both mypy and pyright, "strict" mode enables several error codes that are otherwise disabled by
default, but also makes fundamental changes to the way type inference and type checking works.
Mypy's strict mode includes --check-untyped-defs, for example, without which unannotated
functions are left unchecked; pyright's strict mode includes strictListInference, without which
[1, "foo"] will be inferred as having type list[Unknown] rather than list[int | str] or
similar.
ty's default mode is currently stricter by default than either mypy or pyright in many ways. ty
does not have flags such as --check-untyped-defs or strictListInference, because these are
ty's default behaviour and are not currently configurable. Meanwhile, nearly all ty rules are
enabled by default, and the ones that are disabled by default are usually in that category because
they are either very opinionated or have many false positives.
Recommended configuration
To enable all ty rules at once with the error severity, you can simply use --error=all, but we
wouldn't recommend it. Instead, you can currently approximate something similar to the --strict
mode of other type checkers with the following configuration:
[tool.ty.rules]
dynamic-function-decorator-return = "error"
missing-type-argument = "error"
possibly-unresolved-reference = "warn"
unsound-return-statement = "error"
[tool.ruff.lint]
extend-select = ["ANN", "PYI"]
preview = true
This configuration:
- Enables ty's disabled-by-default
dynamic-function-decorator-return,missing-type-argument,possibly-unresolved-reference, andunsound-return-statementrules - Extends Ruff's default rules with the
ANNandPYIrule categories, both of which are focussed on type-annotating your code more effectively - Enables Ruff's preview mode so that
PYI033also checks.pyfiles
An even stricter configuration -- that goes beyond what mypy and pyright check for in their default
--strict mode in several respects -- might look like this:
[tool.ty.rules]
blanket-ignore-comment = "error"
dynamic-function-decorator-return = "error"
missing-type-argument = "error"
possibly-unresolved-reference = "warn"
unsound-assignment = "error"
unsound-return-statement = "error"
unsound-yield = "error"
unsupported-dynamic-base = "warn"
# NOTE: the following rules are known to have a significant number of false positives,
# which is mostly unavoidable. Enable them at your own risk!
division-by-zero = "warn"
possibly-missing-attribute = "warn"
possibly-missing-import = "warn"
[tool.ty.analysis]
strict-literal-narrowing = true
strict-generic-narrowing = true
[tool.ruff.lint]
extend-select = ["ANN", "PYI", "PGH003"]
preview = true
Note that several checks in mypy and pyright are not yet implemented in ty. See the rule mapping table below for more details.
Mapping pyright/mypy rules to ty/Ruff rules
How to read this table
- ty or Ruff rule: the canonical name, as listed in Rules if it is a ty
rule. Configure ty rules under
[tool.ty.rules]. Where Ruff provides equivalent coverage for a check that has no ty rule, the relevant Ruff rule or rule group is linked instead. - Mypy error code: the value passed to
# type: ignore[<code>]ordisable_error_code. Some ty rules surface as one of mypy's catch-all codes (misc,assignment,valid-type); these mappings are deliberately broad. - Pyright diagnostic: the
report*setting inpyrightconfig.jsonor[tool.pyright].
A diagnostic may appear in multiple rows when it covers distinct cases. A blank cell means no direct equivalent exists in that checker (the diagnostic is either not emitted, or is folded into a broader category that already appears for another ty rule).
Rules
The full list of ty rules — including those without a direct equivalent above — is in
Rules. Contributions to extend this mapping are welcome via pull request to the
ty repository; see issue
#2111 for context.