Unexpected order dependence when assigning to multiple targets
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Description
Bug Report
When assigning an empty generic type to both a typed target and a new not-yet-typed target, typed targets to the left of the not-yet-typed target do not appear to be considered when determining whether or not the not-yet-typed target needs an explicit type annotation.
To Reproduce
typed_list: list[int]
untyped_target = typed_list = [] # All good
typed_list = another_untyped_target = [] # var-annotated error
https://mypy-play.net/?mypy=latest&python=3.12&gist=7d4ec0816e1ea43a3bb6def3f55b3296
The same problem occurs when the typed target is a structured target like self.attr_name or container[key].
Expected Behavior
When assigning to both a structured target and a new local variable name, I prefer to put the structured target first.
I expected to be able to do that without having to put an explicit annotation on the local variable name.
Actual Behavior
Mypy reports the following error when the untyped target is to the right of
error: Need type annotation for "another_untyped_target" (hint: "another_untyped_target: list[<type>] = ...") [var-annotated]
Your Environment
Local environment where the issue was originally noted:
- Mypy version used: 1.16.1
- Mypy command-line flags: --strict
- Python version used: 3.11
Simplified example comes from the MyPy Playground link above (Python 3.12, MyPy 1.17.0)
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Reproduce the assignment-ordering examples in the linked mypy-playground case using mypy 1.16.1 or later with --strict. Trace how multiple-target assignments infer types for local and structured targets; done means the untyped target is accepted when the typed target appears first, without regressing the opposite ordering.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100