code: # --------------------------------------------------------
  # Fast R-CNN
  # Copyright (c) 2015 Microsoft
  # Licensed under The MIT License [see LICENSE for details]
  # Written by Ross Girshick
  # --------------------------------------------------------
  
  import os
  import os.path as osp
  import PIL
  import numpy as np
  import scipy.sparse
  
  from ..utils.cython_bbox import bbox_overlaps
  from PIL import Image
  
  # TODO: make fast_rcnn irrelevant
  # >>>> obsolete, because it depends on sth outside of this project
  from ..fast_rcnn.config import cfg
  
  # <<<< obsolete
  
  ROOT_DIR = osp.join(osp.dirname(__file__), '..', '..')
  MATLAB = 'matlab_r2013b'
  
  
  class imdb(object):
      """Image database."""
  
      def __init__(self, name):
          self._name = name
          self._num_classes = 0
          self._classes = []
          self._image_index = []
          self._obj_proposer = 'selective_search'
          self._roidb = None
          print (self.default_roidb)
          self._roidb_handler = self.default_roidb
          # Use this dict for storing dataset specific config options
          self.config = {}
  
      @property
      def name(self):
          return self._name
  
      @property
      def num_classes(self):
          return len(self._classes)
  
      @property
      def classes(self):
          return self._classes
  
      @property
      def image_index(self):
          return self._image_index
  
      @property
      def roidb_handler(self):
          return self._roidb_handler
  
      @roidb_handler.setter
      def roidb_handler(self, val):
          self._roidb_handler = val
  
      def set_proposal_method(self, method):
          method = eval('self.' + method + '_roidb')
          self.roidb_handler = method
  
      @property
      def roidb(self):
          # A roidb is a list of dictionaries, each with the following keys:
          #   boxes
          #   gt_overlaps
          #   gt_classes
          #   flipped
          if self._roidb is not None:
              return self._roidb
          self._roidb = self.roidb_handler()
          return self._roidb
  
      @property
      def cache_path(self):
          cache_path = osp.abspath(osp.join(cfg.DATA_DIR, 'cache'))
          if not os.path.exists(cache_path):
              os.makedirs(cache_path)
          return cache_path
  
      @property
      def num_images(self):
          return len(self.image_index)
  
      def image_path_at(self, i):
          raise NotImplementedError
  
      def default_roidb(self):
          raise NotImplementedError
  
      def evaluate_detections(self, all_boxes, output_dir=None):
          """
          all_boxes is a list of length number-of-classes.
          Each list element is a list of length number-of-images.
          Each of those list elements is either an empty list []
          or a numpy array of detection.
  
          all_boxes[class][image] = [] or np.array of shape #dets x 5
          """
          raise NotImplementedError
  
      def _get_widths(self):
          return [PIL.Image.open(self.image_path_at(i)).size[0]
                  for i in range(self.num_images)]
  
      def append_flipped_images(self):
          num_images = self.num_images
          widths = self._get_widths()
          for i in range(num_images):
              boxes = self.roidb[i]['boxes'].copy()
              oldx1 = boxes[:, 0].copy()
              oldx2 = boxes[:, 2].copy()
              boxes[:, 0] = widths[i] - oldx2 - 1
              boxes[:, 2] = widths[i] - oldx1 - 1
              assert (boxes[:, 2] >= boxes[:, 0]).all()
              entry = {'boxes': boxes,
                       'gt_overlaps': self.roidb[i]['gt_overlaps'],
                       'gt_classes': self.roidb[i]['gt_classes'],
                       'flipped': True}
  
              if 'gt_ishard' in self.roidb[i] and 'dontcare_areas' in self.roidb[i]:
                  entry['gt_ishard'] = self.roidb[i]['gt_ishard'].copy()
                  dontcare_areas = self.roidb[i]['dontcare_areas'].copy()
                  oldx1 = dontcare_areas[:, 0].copy()
                  oldx2 = dontcare_areas[:, 2].copy()
                  dontcare_areas[:, 0] = widths[i] - oldx2 - 1
                  dontcare_areas[:, 2] = widths[i] - oldx1 - 1
                  entry['dontcare_areas'] = dontcare_areas
  
              self.roidb.append(entry)
  
          self._image_index = self._image_index * 2
  
      def evaluate_recall(self, candidate_boxes=None, thresholds=None,
                          area='all', limit=None):
          """Evaluate detection proposal recall metrics.
  
          Returns:
              results: dictionary of results with keys
                  'ar': average recall
                  'recalls': vector recalls at each IoU overlap threshold
                  'thresholds': vector of IoU overlap thresholds
                  'gt_overlaps': vector of all ground-truth overlaps
          """
          # Record max overlap value for each gt box
          # Return vector of overlap values
          areas = {'all': 0, 'small': 1, 'medium': 2, 'large': 3,
                   '96-128': 4, '128-256': 5, '256-512': 6, '512-inf': 7}
          area_ranges = [[0 ** 2, 1e5 ** 2],  # all
                         [0 ** 2, 32 ** 2],  # small
                         [32 ** 2, 96 ** 2],  # medium
                         [96 ** 2, 1e5 ** 2],  # large
                         [96 ** 2, 128 ** 2],  # 96-128
                         [128 ** 2, 256 ** 2],  # 128-256
                         [256 ** 2, 512 ** 2],  # 256-512
                         [512 ** 2, 1e5 ** 2],  # 512-inf
                         ]
          assert areas.has_key(area), 'unknown area range: {}'.format(area)
          area_range = area_ranges[areas[area]]
          gt_overlaps = np.zeros(0)
          num_pos = 0
          for i in range(self.num_images):
              # Checking for max_overlaps == 1 avoids including crowd annotations
              # (...pretty hacking :/)
              max_gt_overlaps = self.roidb[i]['gt_overlaps'].toarray().max(axis=1)
              gt_inds = np.where((self.roidb[i]['gt_classes'] > 0) &
                                 (max_gt_overlaps == 1))[0]
              gt_boxes = self.roidb[i]['boxes'][gt_inds, :]
              gt_areas = self.roidb[i]['seg_areas'][gt_inds]
              valid_gt_inds = np.where((gt_areas >= area_range[0]) &
                                       (gt_areas <= area_range[1]))[0]
              gt_boxes = gt_boxes[valid_gt_inds, :]
              num_pos += len(valid_gt_inds)
  
              if candidate_boxes is None:
                  # If candidate_boxes is not supplied, the default is to use the
                  # non-ground-truth boxes from this roidb
                  non_gt_inds = np.where(self.roidb[i]['gt_classes'] == 0)[0]
                  boxes = self.roidb[i]['boxes'][non_gt_inds, :]
              else:
                  boxes = candidate_boxes[i]
              if boxes.shape[0] == 0:
                  continue
              if limit is not None and boxes.shape[0] > limit:
                  boxes = boxes[:limit, :]
  
              overlaps = bbox_overlaps(boxes.astype(np.float),
                                       gt_boxes.astype(np.float))
  
              _gt_overlaps = np.zeros((gt_boxes.shape[0]))
              for j in range(gt_boxes.shape[0]):
                  # find which proposal box maximally covers each gt box
                  argmax_overlaps = overlaps.argmax(axis=0)
                  # and get the iou amount of coverage for each gt box
                  max_overlaps = overlaps.max(axis=0)
                  # find which gt box is 'best' covered (i.e. 'best' = most iou)
                  gt_ind = max_overlaps.argmax()
                  gt_ovr = max_overlaps.max()
                  assert (gt_ovr >= 0)
                  # find the proposal box that covers the best covered gt box
                  box_ind = argmax_overlaps[gt_ind]
                  # record the iou coverage of this gt box
                  _gt_overlaps[j] = overlaps[box_ind, gt_ind]
                  assert (_gt_overlaps[j] == gt_ovr)
                  # mark the proposal box and the gt box as used
                  overlaps[box_ind, :] = -1
                  overlaps[:, gt_ind] = -1
              # append recorded iou coverage level
              gt_overlaps = np.hstack((gt_overlaps, _gt_overlaps))
  
          gt_overlaps = np.sort(gt_overlaps)
          if thresholds is None:
              step = 0.05
              thresholds = np.arange(0.5, 0.95 + 1e-5, step)
          recalls = np.zeros_like(thresholds)
          # compute recall for each iou threshold
          for i, t in enumerate(thresholds):
              recalls[i] = (gt_overlaps >= t).sum() / float(num_pos)
          # ar = 2 * np.trapz(recalls, thresholds)
          ar = recalls.mean()
          return {'ar': ar, 'recalls': recalls, 'thresholds': thresholds,
                  'gt_overlaps': gt_overlaps}
  
      def create_roidb_from_box_list(self, box_list, gt_roidb):
          assert len(box_list) == self.num_images, \
              'Number of boxes must match number of ground-truth images'
          roidb = []
          for i in range(self.num_images):
              boxes = box_list[i]
              num_boxes = boxes.shape[0]
              overlaps = np.zeros((num_boxes, self.num_classes), dtype=np.float32)
  
              if gt_roidb is not None and gt_roidb[i]['boxes'].size > 0:
                  gt_boxes = gt_roidb[i]['boxes']
                  gt_classes = gt_roidb[i]['gt_classes']
                  gt_overlaps = bbox_overlaps(boxes.astype(np.float),
                                              gt_boxes.astype(np.float))
                  argmaxes = gt_overlaps.argmax(axis=1)
                  maxes = gt_overlaps.max(axis=1)
                  I = np.where(maxes > 0)[0]
                  overlaps[I, gt_classes[argmaxes[I]]] = maxes[I]
  
              overlaps = scipy.sparse.csr_matrix(overlaps)
              roidb.append({
                  'boxes': boxes,
                  'gt_classes': np.zeros((num_boxes,), dtype=np.int32),
                  'gt_overlaps': overlaps,
                  'flipped': False,
                  'seg_areas': np.zeros((num_boxes,), dtype=np.float32),
              })
          return roidb
  
      @staticmethod
      def merge_roidbs(a, b):
          assert len(a) == len(b)
          for i in range(len(a)):
              a[i]['boxes'] = np.vstack((a[i]['boxes'], b[i]['boxes']))
              a[i]['gt_classes'] = np.hstack((a[i]['gt_classes'],
                                              b[i]['gt_classes']))
              a[i]['gt_overlaps'] = scipy.sparse.vstack([a[i]['gt_overlaps'],
                                                         b[i]['gt_overlaps']])
              a[i]['seg_areas'] = np.hstack((a[i]['seg_areas'],
                                             b[i]['seg_areas']))
          return a
  
      def competition_mode(self, on):
          """Turn competition mode on or off."""
          pass
  
apis: numpy.vstack numpy.zeros_like numpy.zeros numpy.arange numpy.hstack numpy.sort numpy.where