support | operation between typing.Union and strings by elmjag · Pull Request #6983 · RustPython/RustPython

elmjag · 2026-02-03T13:43:10Z

Adds support for performing '|' operation between Union objects and strings, e.g. forward type references.

For example following code:

from typing import Union

U1 = Union[int, str]
U1 | "float"

The result of the operation above becomes:

int | str | ForwardRef('float')

Summary by CodeRabbit

Refactor
- Union-type combination now follows a typing-based path with a fast path for common cases, improving correctness and error handling.
- Internal typing helper consolidated into a shared typing call to simplify type-variable and typing operations.
- Reduced public exposure of an internal unionability helper while preserving outward union behavior.

coderabbitai · 2026-02-03T13:43:38Z

📝 Walkthrough

Walkthrough

Type's or_ now delegates union construction to a new public union::or_op, which applies a fast-path unionability check or falls back to typing._type_check before constructing the union.

Changes

Cohort / File(s)	Summary
Type delegation `crates/vm/src/builtins/type.rs`	Replaced manual union checks and tuple construction in `or_` with a call to `union::or_op(zelf, other, vm)`.
Union module refactor & API `crates/vm/src/builtins/union.rs`	Added public `or_op(zelf, other, vm)`; introduced private helpers `type_check` and `has_union_operands`; reduced visibility of `is_unionable` and `make_parameters`; `or_op` performs fast-path checks or delegates to typing-based `_type_check` then calls `make_union`.
Typing helper exposed `crates/vm/src/stdlib/typing.rs`	Added public `call_typing_func_object` to import `typing` and call its functions; removed an internal duplicate helper.
TypeVar wiring `crates/vm/src/stdlib/typevar.rs`	Replaced local `_call_typing_func_object` usages with the new `call_typing_func_object` import and removed the local helper.

Sequence Diagram(s)

sequenceDiagram
    participant Caller
    participant Type as crates::vm::builtins::type::or_
    participant Union as crates::vm::builtins::union::or_op
    participant Typing as typing._type_check
    participant MakeUnion as make_union

    Caller->>Type: or_(left, right)
    Type->>Union: or_op(left, right, vm)
    Union->>Union: has_union_operands / is_unionable fast-path
    alt fast-path
        Union-->>Type: use operand(s) directly
    else fallback
        Union->>Typing: call typing._type_check(arg, message)
        Typing-->>Union: validated/adjusted arg or error
    end
    Union->>MakeUnion: make_union(tuple_of_two_args)
    MakeUnion-->>Union: union object
    Union-->>Type: return union
    Type-->>Caller: return result

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

relocate Generic under typevar.rs #5889 — related changes around factoring typing helpers and typevar/typing call sites.
typevar as module #6834 — similar adjustments to typing/typevar call helper wiring and imports.
typing.TypeVar #5834 — touches typing-call helper integration and typing-based type checking paths.

Suggested reviewers

arihant2math

Poem

🐰 I hopped from Type into Union's lair,
Swapped checks for a shortcut, light as air.
A calling to Typing, a tuple in tow,
Then make_union hummed — and off we go! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 41.18% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'support \| operation between typing.Union and strings' clearly describes the main feature being added—enabling the bitwise-or operator for Union types with string references, which aligns with the changeset's core functionality.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

📝 Generate docstrings

🧪 Generate unit tests (beta)

Create PR with unit tests
Post copyable unit tests in a comment

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coderabbitai

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@crates/vm/src/builtins/union.rs`:
- Around line 206-214: The helper function _call_typing_func_object is
duplicated in union.rs, typing.rs, and typevar.rs; extract it into a single pub
function at module level in typing.rs (make the existing implementation public,
e.g., pub fn _call_typing_func_object(...)) and remove the duplicate definitions
in union.rs and typevar.rs, replacing them with a use/import of the shared
function (call the same symbol _call_typing_func_object) and call it where
needed; ensure the signature stays compatible with VirtualMachine, AsPyStr and
IntoFuncArgs so existing call sites (including code using TypeAliasType in
union.rs) compile without further edits.

🧹 Nitpick comments (1)

crates/vm/src/builtins/union.rs (1)

240-252: Consider using the ? operator for cleaner error propagation.

The match statements can be simplified using Rust's ? operator.

♻️ Suggested simplification

-    let left = match type_check(zelf, vm) {
-        Ok(v) => v,
-        err => {
-            return err;
-        }
-    };
-
-    let right = match type_check(other, vm) {
-        Ok(v) => v,
-        err => {
-            return err;
-        }
-    };
+    let left = type_check(zelf, vm)?;
+    let right = type_check(other, vm)?;

crates/vm/src/builtins/union.rs

youknowone · 2026-02-03T15:16:26Z

crates/vm/src/builtins/union.rs

+    let left = match type_check(zelf, vm) {
+        Ok(v) => v,
+        err => {
+            return err;
+        }
+    };


Suggested change

let left = match type_check(zelf, vm) {

Ok(v) => v,

err => {

return err;

}

};

let left = type_check(zelf, vm)?;

Ahh, yes. Changed to use ?.

Move _call_typing_func_object() code to stdlib::typing::call_typing_func_object(). Use that function everywhere.

Adds support for performing '|' operation between Union objects and strings, e.g. forward type references. For example following code: from typing import Union U1 = Union[int, str] U1 | "float" The result of the operation above becomes: int | str | ForwardRef('float')

github-actions · 2026-02-04T12:06:18Z

📦 Library Dependencies

The following Lib/ modules were modified. Here are their dependencies:

[x] lib: cpython/Lib/typing.py
[ ] test: cpython/Lib/test/test_typing.py (TODO: 20)
[ ] test: cpython/Lib/test/test_type_aliases.py
[ ] test: cpython/Lib/test/test_type_annotations.py
[ ] test: cpython/Lib/test/test_type_params.py
[ ] test: cpython/Lib/test/test_genericalias.py (TODO: 3)

dependencies:

typing

dependent tests: (10 tests)

typing: test_builtin test_enum test_fractions test_functools test_genericalias test_grammar test_importlib test_isinstance test_types test_typing

Legend:

[+] path exists in CPython
[x] up-to-date, [ ] outdated

youknowone

@elmjag Thank you so much for contributing! And welcome to RustPython project.

moreal

Thank you for contribution!

elmjag force-pushed the union-or branch from 7d0eedd to 912bff5 Compare February 3, 2026 13:59

coderabbitai bot reviewed Feb 3, 2026

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crates/vm/src/builtins/union.rs Outdated Show resolved Hide resolved

youknowone reviewed Feb 3, 2026

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elmjag added 2 commits February 4, 2026 12:57

remove duplicated _call_typing_func_object() functions

3d99a79

Move _call_typing_func_object() code to stdlib::typing::call_typing_func_object(). Use that function everywhere.

elmjag force-pushed the union-or branch from 912bff5 to 411f549 Compare February 4, 2026 12:05

youknowone approved these changes Feb 4, 2026

View reviewed changes

moreal approved these changes Feb 4, 2026

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youknowone merged commit ffc4622 into RustPython:main Feb 4, 2026
24 of 25 checks passed

elmjag deleted the union-or branch February 4, 2026 15:19

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support | operation between typing.Union and strings#6983

support | operation between typing.Union and strings#6983
youknowone merged 2 commits intoRustPython:mainfrom
elmjag:union-or

elmjag commented Feb 3, 2026 •

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Walkthrough

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Sequence Diagram(s)

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📦 Library Dependencies

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elmjag commented Feb 3, 2026 •

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