python / python/mypy

In a function call, if a variable accessed in an iteratable doesn't have an attribute, mypy picks the first overload available, creating spurious further list-item errors.

Abierto
#17,082 0 comentarios 0 reacciones 0 asignados Ver en GitHub

Nadie ha tomado este issue todavía.

bug
Lenguaje dominante
Python
Estrellas
20.6k
Forks
3.3k
Métricas de merge de PR
Métricas de PR pendientes

Descripción

Bug Report

If a variable accessed in an iteratable doesn't have an attribute ([attr-defined] error), and that iterable is then passed to a function, mypy seems to pick the first overload available to continue typechecking against that function, creating spurious further list-item errors, even when more information is available to deduce the correct type. The code below should make more clear what I mean.

To Reproduce
mypy-play gist

from typing import Any, Iterable, overload

d = 42 #example value without attributes

@overload
def foo(x: Iterable[str]) -> None: ...
@overload
def foo(x: Iterable[int]) -> None: ...

def foo(x: Any) -> None:
  return None

# Pass the checker, correctly
foo(["ok", "ok"])
foo([1, 1])

# Fail the checker, correctly, with [list-item] errors (although they all assume the str override is the authoritative one)
foo(["ok", 1])
foo([1, "ok"])
foo([None, "ok"])

# Fail the checker, but the int ones generate spurious list-item errors.
foo(["ok", d.x])
foo([2, d.x])
foo([d.x, "ok"])
foo([d.x, 2])

# This doesn't generate an [attr-defined] error, but still produces a spurious list-item error!
foo([d.x, 2]) #type: ignore[attr-defined]

Expected Behavior

If a function is declared to take an Iterable, with multiple types of Iterable specified by overload decorators, then an [attr-defined] error inside the iterable the function is called upon should not prevent mypy from deducing the correct type of that iterable from its other contents. The correct type of the iterable should still be deduced.

Actual Behavior

However, what actually happens is that if an [attr-defined] error occurs inside of the list I am passing to the function, mypy just choses the first overload. In this case, Iterable[str]. Therefore, spurious [list-item] errors are created when the other member of the list is an int. The [list-item] errors in the below output for lines 24, 26, and 29 are spurious:

test.py:18: error: List item 1 has incompatible type "int"; expected "str"  [list-item]
test.py:19: error: List item 0 has incompatible type "int"; expected "str"  [list-item]
test.py:20: error: List item 0 has incompatible type "None"; expected "str"  [list-item]
test.py:23: error: "int" has no attribute "x"  [attr-defined]
test.py:24: error: List item 0 has incompatible type "int"; expected "str"  [list-item]
test.py:24: error: "int" has no attribute "x"  [attr-defined]
test.py:25: error: "int" has no attribute "x"  [attr-defined]
test.py:26: error: "int" has no attribute "x"  [attr-defined]
test.py:26: error: List item 1 has incompatible type "int"; expected "str"  [list-item]
test.py:29: error: List item 1 has incompatible type "int"; expected "str"  [list-item]
test.py:29: note: Error code "list-item" not covered by "type: ignore" comment
Found 10 errors in 1 file (checked 1 source file)

Here is a --pretty listing of the relevant errors:

test.py:24: error: List item 0 has incompatible type "int"; expected "str"  [list-item]
    foo([2, d.x])
         ^
test.py:24: error: "int" has no attribute "x"  [attr-defined]
    foo([2, d.x])
            ^~~
test.py:26: error: "int" has no attribute "x"  [attr-defined]
    foo([d.x, 2])
         ^~~
test.py:26: error: List item 1 has incompatible type "int"; expected "str"  [list-item]
    foo([d.x, 2])
              ^
test.py:29: error: List item 1 has incompatible type "int"; expected "str"  [list-item]
    foo([d.x, 2]) #type: ignore[attr-defined]
test.py:29: note: Error code "list-item" not covered by "type: ignore" comment

29 is especially annoying, because the [attr-defined] ignore does not suppress all warnings that indirectly result from the [attr-defined] error!

You can also switch the order of the overloads in the code to see that mypy now complains that its arguments are str when it needs ints, instead of vice-versa.

Your Environment

  • Mypy version used: 1.9.0
  • Mypy command-line flags: none
  • Mypy configuration options from mypy.ini (and other config files): n/a
  • Python version used: Python 3.11.0 and 3.12

Guía de contribución

Abrir la guía de contribución

Primeros pasos

  1. Lee el issue completo y luego la guía de contribución del proyecto.
  2. Comenta en el issue que vas a ocuparte — evita que dos personas hagan lo mismo.
  3. Haz un fork del repositorio y trabaja en una rama.
  4. Abre un pull request que haga referencia al número del issue.

Línea de trabajo

Empieza reproduciendo el problema a partir del ejemplo incluido o del gist de mypy-play enlazado con mypy 1.9.0, incluyendo el orden de las sobrecargas y el caso con attr-defined ignorado. Sigue la selección de sobrecargas y la inferencia de los elementos del iterable y, después, añade cobertura de regresión que demuestre que los elementos conocidos de la lista determinan la sobrecarga correcta sin generar errores list-item espurios, mientras el error attr-defined permanece.

Escrito por el modelo de indexación a partir del texto del issue.

Evaluación

Stack tecnológico
python
Área
compilers, devtools
Tipo de issue
Error
Dificultad
4/5
Tiempo estimado
3-5 días
Estado de actividad
Estancado
Claridad
Bien especificado
Aptitud para principiantes
52/100

Recibe los nuevos issues en tu correo

Un resumen breve de issues de GitHub para principiantes.