annotations导入报错

转自

　　「 不止于python 」

相关环境版本

python 3.7.10
fastapi 0.63.0
Cython 0.29.22

报错文件

# main.py
from __future__ import annotations
......# code

报错信息

1. 

is not defined
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/dist-packages/Cython/Build/Dependencies.py", line 1249, in cythonize_one_helper
    return cythonize_one(*m)
  File "/usr/local/lib/python3.7/dist-packages/Cython/Build/Dependencies.py", line 1225, in cythonize_one
    raise CompileError(None, pyx_file) 

 2. 

Traceback (most recent call last):
  File "/usr/lib/python3.5/py_compile.py", line 125, in compile
    _optimize=optimize)
  File "", line 735, in source_to_code
  File "", 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:

报错原因

1. 使用Cython版本过低

　　https://github.com/cython/cython/issues/2950#issuecomment-679136993

2. 使用python3.7以下版本
   　报错: https://stackoverflow.com/questions/52889746/cant-import-annotations-from-future/52890129

　　　根据PEP-563在py3.7中才能使用

    　　https://www.python.org/dev/peps/pep-0563/#enabling-the-future-behavior-in-python-3-7

报错解决

 1.升级Cython, 使用3.0版本

pip3.7 install Cython==3.0a1

2.使用python3.7以上版本

相关链接 

https://github.com/cython/cython/issues/2950

https://stackoverflow.com/questions/52889746/cant-import-annotations-from-future/52890129

https://www.python.org/dev/peps/pep-0563/#enabling-the-future-behavior-in-python-3-7