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

此错误可能是什么原因？

Answer 1

查看您的错误回溯，看来您正在使用python 3.5。是这样吗？

如果是这样，则会发生错误，因为根据PEP-563，从__future__开始可以导入annotations Python 3.7。

我没有发现任何暗示它会被反向移植到以前的版本，但是我可能已经错过了。