code: import numpy as np
  from .config import cfg
  pure_python_nms = False
  try:
      from lib.utils.gpu_nms import gpu_nms
      from ..utils.cython_nms import nms as cython_nms
  except ImportError:
      pure_python_nms = True
  
  
  def nms(dets, thresh):
      if dets.shape[0] == 0:
          return []
      if pure_python_nms:
          # print("Fall back to pure python nms")
          return py_cpu_nms(dets, thresh)
      if cfg.USE_GPU_NMS:
          return gpu_nms(dets, thresh, device_id=cfg.GPU_ID)
      else:
          return cython_nms(dets, thresh)
  
  
  def py_cpu_nms(dets, thresh):
      x1 = dets[:, 0]
      y1 = dets[:, 1]
      x2 = dets[:, 2]
      y2 = dets[:, 3]
      scores = dets[:, 4]
  
      areas = (x2 - x1 + 1) * (y2 - y1 + 1)
      order = scores.argsort()[::-1]
  
      keep = []
      while order.size > 0:
          i = order[0]
          keep.append(i)
          xx1 = np.maximum(x1[i], x1[order[1:]])
          yy1 = np.maximum(y1[i], y1[order[1:]])
          xx2 = np.minimum(x2[i], x2[order[1:]])
          yy2 = np.minimum(y2[i], y2[order[1:]])
          w = np.maximum(0.0, xx2 - xx1 + 1)
          h = np.maximum(0.0, yy2 - yy1 + 1)
          inter = w * h
          ovr = inter / (areas[i] + areas[order[1:]] - inter)
          inds = np.where(ovr <= thresh)[0]
          order = order[inds + 1]
      return keep
  
apis: numpy.maximum numpy.where numpy.minimum