TypeVar with Type-based constraints misbehaving when used to annotate *args
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Description
Bug Report
It seems that the below combination of *args, and TypeVar with constraints related to Type, is misbehaving. I reached out on the Gitter and was instructed that this is probably a bug.
I tried replacing the Types with ints (observable in the linked mypy-playground) and that seems to work fine.
To Reproduce
from typing import TypeVar, List, Type
TypeArgT = TypeVar("TypeArgT", Type, List[Type])
def type_a(*args: TypeArgT):
...
def type_b(*args: List[Type]):
...
type_a(int, str, float) # test t1
type_a([str, float], [int]) # test t2 <-- this does not work
type_b([bool, bool], [str, bool]) # test t3
https://mypy-play.net/?mypy=0.780&python=3.8&gist=847224369f6bad4d74a1ccfd672fb250
Actual Behavior
Test t2 in the above snippet throws the following mypy error:
main.py:14: error: Value of type variable "TypeArgT" of "type_a" cannot be "object"
Found 1 error in 1 file (checked 1 source file)
Your Environment
- Mypy version used: 0.790
- Python version used: 3.8
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
No project file or test is named. Start by running the reproduction against mypy 0.790, then trace inference for constrained TypeVar values used with *args; done means t2 is accepted without changing the existing t1 and t3 behavior.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers, devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 42/100