VSCode中Pylance对Python类方法类型注解报错求助

问题说明 #

VSCode 1.83.0搭配Pylance v2023.10.20时，所有类的classmethod类型注解都会触发错误警告。示例代码如下：

from __future__ import annotations

class A:
    @classmethod
    def foo(cls: type[A]) -> str:
        return "bar"

Pylance给出的报错信息：

Argument of type "(cls: type[A]) -> str" cannot be assigned to parameter "__f" of type "() -> _R_co@classmethod" in function "__init__"
Type "(cls: type[A]) -> str" cannot be assigned to type "() -> _R_co@classmethod"PylancereportGeneralTypeIssues

当前VSCode的settings.json配置：

{
  "editor.formatOnSave": true,
  "editor.rulers": [140],
  "flake8.args": ["--config=setup.cfg"],
  "flake8.path": ["${workspaceFolder}/venv/bin/python", "-m", "flake8"],
  "[python]": {
    "editor.defaultFormatter": "ms-python.black-formatter",
    "editor.formatOnSave": true
  },
  "black-formatter.args": ["--line-length", "120"],
  "mypy-type-checker.args": ["--config-file=setup.cfg"],
  "mypy-type-checker.path": [
    "${workspaceFolder}/venv/bin/python",
    "-m",
    "mypy"
  ],
  "python.languageServer": "Pylance",
  "python.analysis.typeCheckingMode": "basic",
  "files.exclude": {
    "**/.git": true,
    "**/.svn": true,
    "**/.hg": true,
    "**/CVS": true,
    "**/.DS_Store": true,
    "**/Thumbs.db": true,
    "**/__pycache__": true,
    "**/.pytest_cache": true,
    "**/.mypy_cache": true,
    "**/venv": true
  },
  "python.defaultInterpreterPath": "${workspaceFolder}/venv/bin/python",
  "autoDocstring.docstringFormat": "google-notypes"
}

setup.cfg配置：

[flake8]
max-line-length = 120
extend-ignore =
    # no whitespace before colon on list slice
    E203,
    # line break occurred before a binary operator
    W503,
    # comparison to True should be is not == (not true for pandas)
    E712,
    # line too long (handled by formatter automatically whenever possible)
    E501,
    # missing type annotation for self in method
    ANN101,
    # missing type annotation for *args, **kwargs
    ANN002,
    ANN003
per-file-ignores =
    # imported but unused
    __init__.py: F401
exclude = .vscode, .git, __pycache__, venv, tests
require-plugins = flake8-annotations, flake8-pep585
# infer no return as a None return type
suppress-none-returning = true
# for mypy
mypy-init-return = true
# allow importing from typing for convenience
pep585-whitelisted-symbols =
    Iterator
    Iterable
    Callable

[mypy]
exclude = .vscode, .git, __pycache__, venv, tests
strict_optional = False

解决方案 #

1. 升级Pylance版本 #

你用的Pylance v2023.10.20存在classmethod类型注解的兼容性bug，后续版本已经修复了这个问题。直接在VSCode扩展市场搜索Pylance，点击更新到最新版本即可解决。

2. 调整类型注解写法（兼容旧版本） #

如果暂时无法升级，可修改cls的类型注解为Type[A]（需要从typing导入），或者直接省略cls的类型注解（Pylance会自动推断类型）：

# 写法1：导入Type
from __future__ import annotations
from typing import Type

class A:
    @classmethod
    def foo(cls: Type[A]) -> str:
        return "bar"

# 写法2：省略cls的类型注解
from __future__ import annotations

class A:
    @classmethod
    def foo(cls) -> str:
        return "bar"

3. 临时禁用该类型检查规则 #

如果需要快速屏蔽报错，可在VSCode的settings.json中添加以下配置：

"python.analysis.diagnosticSeverityOverrides": {
    "reportGeneralTypeIssues": "none"
}

注意：这个方法会禁用所有reportGeneralTypeIssues类的警告，建议优先使用前两种方案。

内容的提问来源于stack exchange，提问作者Avinash Raj