安装Python版darkflow时遭遇Cython编译错误，求解决方案

执行pip install .安装darkflow项目时，出现Cython编译失败，报错找不到nms.pxd文件、NMS无法识别为合法标识符，最终导致metadata生成失败。

错误详情 #

C:\Users\navin\Desktop\smt4\Smart-traffic-control-system-with-python\darkflow>pip install .
Processing c:\users\navin\desktop\smt4\smart-traffic-control-system-with-python\darkflow
  Preparing metadata (setup.py) ... error
  error: subprocess-exited-with-error
  
  × python setup.py egg_info did not run successfully.
  │ exit code: 1
  ╰─> [60 lines of output]
      C:\Users\navin\Desktop\smt4\Smart-traffic-control-system-with-python\darkflow\setup.py:6: DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
        import imp
      c:\users\navin\appdata\local\programs\python\python39\lib\site-packages\Cython\Compiler\Main.py:381: FutureWarning: Cython directive 'language_level' not set, using '3str' for now (Py3). This has changed from earlier releases! File: C:\Users\navin\Desktop\smt4\Smart-traffic-control-system-with-python\darkflow\darkflow\cython_utils\cy_yolo2_findboxes.pyx
        tree = Parsing.p_module(s, pxd, full_module_name)

      Error compiling Cython file:
      ------------------------------------------------------------
      ...
      cimport numpy as np
      cimport cython
      ctypedef np.float_t DTYPE_t
      from libc.math cimport exp
      from ..utils.box import BoundBox
      from nms cimport NMS
      ^
      ------------------------------------------------------------

      darkflow\cython_utils\cy_yolo2_findboxes.pyx:7:0: 'nms.pxd' not found

      Error compiling Cython file:
      ------------------------------------------------------------
      ...
      cimport numpy as np
      cimport cython
      ctypedef np.float_t DTYPE_t
      from libc.math cimport exp
      from ..utils.box import BoundBox
      from nms cimport NMS
      ^
      ------------------------------------------------------------

      darkflow\cython_utils\cy_yolo2_findboxes.pyx:7:0: 'nms\NMS.pxd' not found

      Error compiling Cython file:
      ------------------------------------------------------------
      ...
                          if(tempc > threshold):
                              probs[row, col, box_loop, class_loop] = tempc


          #NMS
          return NMS(np.ascontiguousarray(probs).reshape(H*W*B,C), np.ascontiguousarray(Bbox_pred).reshape(H*B*W,5))
                 ^
      ------------------------------------------------------------

      darkflow\cython_utils\cy_yolo2_findboxes.pyx:97:11: 'NMS' is not a constant, variable or function identifier
      Traceback (most recent call last):
        File "<string>", line 2, in <module>
        File "<pip-setuptools-caller>", line 34, in <module>
        File "C:\Users\navin\Desktop\smt4\Smart-traffic-control-system-with-python\darkflow\setup.py", line 73, in <module>
          ext_modules = cythonize(ext_modules)
        File "c:\users\navin\appdata\local\programs\python\python39\lib\site-packages\Cython\Build\Dependencies.py", line 1154, in cythonize
          cythonize_one(*args)
        File "c:\users\navin\appdata\local\programs\python\python39\lib\site-packages\Cython\Build\Dependencies.py", line 1321, in cythonize_one       
          raise CompileError(None, pyx_file)
      Cython.Compiler.Errors.CompileError: darkflow/cython_utils/cy_yolo2_findboxes.pyx
      Compiling darkflow/cython_utils/nms.pyx because it changed.
      Compiling darkflow/cython_utils/cy_yolo2_findboxes.pyx because it changed.
      Compiling darkflow/cython_utils/cy_yolo_findboxes.pyx because it changed.
      [1/3] Cythonizing darkflow/cython_utils/cy_yolo2_findboxes.pyx
      [end of output]

  note: This error originates from a subprocess, and is likely not a problem with pip.
error: metadata-generation-failed

× Encountered error while generating package metadata.
╰─> See above for output.

note: This is an issue with the package mentioned above, not pip.
hint: See above for details.

C:\Users\navin\Desktop\smt4\Smart-traffic-control-system-with-python\darkflow>

可行解决方案 #

方案1：修复Cython文件的相对导入路径 #

报错核心原因是cy_yolo2_findboxes.pyx中对nms的导入路径不正确，按以下步骤修改：

• 打开darkflow/cython_utils/cy_yolo2_findboxes.pyx文件
• 将第7行的from nms cimport NMS修改为from .nms cimport NMS（添加相对路径前缀.）
• 保存文件后重新执行pip install .

方案2：指定Cython语言版本 #

针对报错中提到的language_level未设置问题，修改项目根目录的setup.py：

• 找到ext_modules = cythonize(ext_modules)这一行
• 修改为ext_modules = cythonize(ext_modules, language_level="3")
• 保存后重新执行安装命令

方案3：使用兼容的Python和Cython版本 #

darkflow对新版本Python、Cython兼容性较差，建议降级到以下版本：

• Python 3.7或3.8（避免使用3.9及以上版本）
• Cython 0.29.x版本（避免使用3.0及以上版本）
  先执行降级命令：

pip install cython==0.29.36

之后再执行pip install .

方案4：手动预编译Cython文件 #

先手动编译所有Cython文件，再执行安装：

cd darkflow/cython_utils
cython nms.pyx
cython cy_yolo2_findboxes.pyx
cython cy_yolo_findboxes.pyx
cd ../..
pip install .

内容的提问来源于stack exchange，提问作者navinisha mohan