Question

直接从typing文档中考虑以下typing.TypeVar的图示：

# mypytest.py
from typing import TypeVar

A = TypeVar("A", str, bytes)  # I.e. typing.AnyStr

def longest(x: A, y: A) -> A:
    """Return the longest of two strings."""
    # https://docs.python.org/3/library/typing.html
    return x if len(x) >= len(y) else y

调用mypy mypytest.py不会产生任何错误并退出0。在此示例中，目的是A可以是str或bytes，但是返回类型将与传递的类型。

但是，当存在默认参数时，mypy将引发错误：

def longest_v2(x: A = "foo", y: A = "bar") -> A:
    return x if len(x) >= len(y) else y

提高：

$ mypy mypytest.py
mypytest.py:11: error: Incompatible default for argument "x" (default has type "str", argument has type "bytes")
mypytest.py:11: error: Incompatible default for argument "y" (default has type "str", argument has type "bytes")

为什么在第二种情况下会发生错误？

带有行号：

  1 # mypytest.py
  2 from typing import TypeVar
  3
  4 A = TypeVar("A", str, bytes)  # I.e. typing.AnyStr
  5
  6 def longest(x: A, y: A) -> A:
  7     """Return the longest of two strings."""
  8     # https://docs.python.org/3/library/typing.html
  9     return x if len(x) >= len(y) else y
 10
 11 def longest_v2(x: A = "foo", y: A = "bar") -> A:
 12     return x if len(x) >= len(y) else y

mypy“参数的默认默认值不兼容”，关键字为arg默认值

0 个答案: