python - 无法从 __future__ 导入注释

Question

运行语句时

from __future__ import annotations

我收到以下错误:

Traceback (most recent call last):
  File "/usr/lib/python3.5/py_compile.py", line 125, in compile
    _optimize=optimize)
  File "<frozen importlib._bootstrap_external>", line 735, in source_to_code
  File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
  File "./prog.py", line 1
    from __future__ import annotations
    ^
SyntaxError: future feature annotations is not defined

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python3.5/py_compile.py", line 129, in compile
    raise py_exc
py_compile.PyCompileError:   File "./prog.py", line 1
    from __future__ import annotations
                                     ^
SyntaxError: future feature annotations is not defined

这个错误的原因可能是什么？

Answer 1

查看您的错误回溯，看起来您使用的是 python 3.5。是这样吗？

如果是这样，那么错误就会发生，因为根据 PEP-563 __future__ annotations 的导入从 Python 3.7 开始可用。

我没有发现任何暗示这将被移植到以前的版本，但我可能错过了。