python / python/mypy

Mypy error with tuple types Including TypedDict in return

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bug topic-type-context topic-typed-dict
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Python
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Description

Bug Report

When using multiple tuple types, one of which includes TypedDict as a return value type, mypy generates errors.

from typing import TypedDict

class MyTypedDict1(TypedDict):
    a: int

class MyTypedDict2(TypedDict):
    b: int

def success_func1(x: int) -> MyTypedDict1:
    return {"a": x}

def success_func2(x: int) -> tuple[MyTypedDict1, int]:
    return {"a": x}, 1

def success_func3(x: int) -> MyTypedDict1 | MyTypedDict2:
    if x > 0:
        return {"a": x}
    return {"b": x}

def success_func4(x: int) -> tuple[int, float] | tuple[str, float]:
    if x > 0:
        return 1, 1.0
    return "1", 1.0

def success_func5(x: int) -> tuple[int, MyTypedDict1] | str:
    if x > 0:
        return 1, {"a": 1}
    return "1"

def success_func6(x: int) -> tuple[int, MyTypedDict1] | tuple[str]:
    if x > 0:
        return 1, {"a": 1}
    return ("1",)

def success_func7(x: int) -> tuple[int, dict[str, int]] | tuple[str, int]:
    if x > 0:
        return 1, {"a": 1}
    return "1", 1

def success_func8(x: int) -> tuple[int | str, MyTypedDict1 | MyTypedDict2]:
    if x > 0:
        return 1, {"a": x}
    return "1", {"b": x}

def mypy_err_func1(x: int) -> tuple[int, MyTypedDict1] | tuple[str, float]:
    if x > 0:
        return 1, {"a": 1}
    return "1", 1.0

def mypy_err_func2(x: int) -> tuple[int, MyTypedDict1] | tuple[str, MyTypedDict2]:
    if x > 0:
        return 1, {"a": x}
    return "1", {"b": x}

print(success_func1(1))
print(success_func2(1))
print(success_func3(1))
print(success_func4(1))
print(success_func5(1))
print(success_func6(1))
print(success_func7(1))
print(success_func8(1))
print(mypy_err_func1(1))
print(mypy_err_func2(1))

https://mypy-play.net/?mypy=master&python=3.11&gist=420e018ad82fe72420a40e4b05eb1275

Expected Behavior

$mypy tmp.py
Success: no issues found in 1 source file

Actual Behavior

$mypy tmp.py
tmp.py:47: error: Incompatible return value type (got "tuple[int, dict[str, int]]", expected "tuple[int, MyTypedDict1] | tuple[str, float]")  [return-value]
tmp.py:52: error: Incompatible return value type (got "tuple[int, dict[str, int]]", expected "tuple[int, MyTypedDict1] | tuple[str, MyTypedDict2]")  [return-value]
tmp.py:53: error: Incompatible return value type (got "tuple[str, dict[str, int]]", expected "tuple[int, MyTypedDict1] | tuple[str, MyTypedDict2]")  [return-value]
Found 3 errors in 1 file (checked 1 source file)

Your Environment

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running the issue's minimal example with mypy 1.7.1 or the linked mypy-play reproduction, focusing on the three reported return-value errors involving tuple unions and TypedDict. Trace the relevant tuple and TypedDict compatibility checks in mypy's type-checking code. Done means the example reports no issues while preserving the existing successful cases.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

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