Pyrefly 1.4.0

*Release date：September 28, 2026*

Pyrefly v1.3.2 is a patch release that fixes regressions in how Pyrefly infers the type of a variable after it is assigned a value of type Any.

🐛 Bug fixes

• #4846: Fixed several regressions from v1.3.0 in type inference after a variable is reassigned to Any:
• Assigning an implicit Any (a value with no known type, such as the result of an unannotated function or an unresolved import) to an annotated variable once again produces Unknown. It no longer turns into an explicit Any.
• When a variable annotated as Optional[T] or T | None is narrowed to None and then reassigned inside that branch, Pyrefly no longer adds the annotation's None back after the branch. For example, x：Any | None followed by if x is None: x = get_any() now gives Any instead of Any | None.
• When a variable's annotation is a union that contains Any, assigning Any to it now narrows the variable to Any. For example, x：Any | None followed by x = x or get_any() now gives Any instead of Any | None, so later attribute access no longer reports a false missing-attribute error on None.

Thank-you to all our contributors who found these bugs and reported them! Did you know this is one of the most helpful contributions you can make to an open-source project? If you find any bugs in Pyrefly we want to know about them! Please open a bug report issue here.

📦 Upgrade
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*Release date: July 31, 2026*

Pyrefly v1.2.0 bundles 901 commits from 59 contributors.

✨ New & Improved

Type Checking

Attrs classes are now fully supported with comprehensive field synthesis, validation, and special-method generation. Pyrefly recognizes @attr.s, @define, @frozen, and their variants, handling field specifiers (attr.ib(), field()), converters, validators, defaults, and private-field aliasing. Converters are typed from their real input type rather than Any, including the @<field>.converter decorator, attrs.converters.pipe, attrs.converters.default_if_none, and generic converters like copy.deepcopy. See the new attrs documentation for details.
functools.partial is now type-checked instead of treated as opaque. Bound arguments are validated at construction and Pyrefly synthesizes a precise residual signature for the remaining parameters, so errors surface at both the partial(...) call and the later invocation. Generic functions, overloads, constructors, bound methods, and Unpack[TypedDict] parameters are supported, and results expose .func, .args, and .keywords. Precise residual callable assignment is enabled by the strict and all presets or explicitly with strict-partial-subtyping. …

Release date: June 18, 2026

Pyrefly v1.1.1 is a patch release with a single bug fix.

🐛 Bug fixes

- #3867: Fixed a regression introduced in 1.1.0 where isinstance() narrowing of a union variable
silently stopped working when an earlier sibling branch in the same if/elif/else chain narrowed
a different variable with isinstance() and returned. The later narrowing left the union
untouched, producing false missing-attribute errors on code that checked correctly in 1.0.0.

Thank-you to all our contributors who found these bugs and reported them! Did you know this is one
of the most helpful contributions you can make to an open-source project? If you find any bugs in
Pyrefly we want to know about them! Please open a bug report issue here.