Support for returning multiple targets (#700)

Author: TheCodez

torchvision/datasets/cityscapes.py

@@ -7,18 +7,45 @@
 
 class Cityscapes(data.Dataset):
     """`Cityscapes <http://www.cityscapes-dataset.com/>`_ Dataset.
+
     Args:
         root (string): Root directory of dataset where directory ``leftImg8bit``
             and ``gtFine`` or ``gtCoarse`` are located.
         split (string, optional): The image split to use, ``train``, ``test`` or ``val`` if mode="gtFine"
             otherwise ``train``, ``train_extra`` or ``val``
         mode (string, optional): The quality mode to use, ``gtFine`` or ``gtCoarse``
-        target_type (string, optional): Type of target to use, ``instance``, ``semantic``, ``polygon``
-            or ``color``
+        target_type (string or list, optional): Type of target to use, ``instance``, ``semantic``, ``polygon``
+            or ``color``. Can also be a list to output a tuple with all specified target types.
         transform (callable, optional): A function/transform that takes in a PIL image
             and returns a transformed version. E.g, ``transforms.RandomCrop``
         target_transform (callable, optional): A function/transform that takes in the
             target and transforms it.
+
+    Examples:
+
+        Get semantic segmentation target
+
+        .. code-block:: python
+            dataset = Cityscapes('./data/cityscapes', split='train', mode='gtFine',
+                                 target_type='semantic')
+
+            img, smnt = dataset[0]
+
+        Get multiple targets
+
+        .. code-block:: python
+            dataset = Cityscapes('./data/cityscapes', split='train', mode='gtFine',
+                                 target_type=['instance', 'color', 'polygon'])
+
+            img, (inst, col, poly) = dataset[0]
+
+        Validate on the "gtCoarse" set
+
+        .. code-block:: python
+            dataset = Cityscapes('./data/cityscapes', split='val', mode='gtCoarse',
+                                 target_type='semantic')
+
+            img, smnt = dataset[0]
     """
 
     def __init__(self, root, split='train', mode='gtFine', target_type='instance',
@@ -44,9 +71,12 @@ def __init__(self, root, split='train', mode='gtFine', target_type='instance',
             raise ValueError('Invalid split for mode "gtCoarse"! Please use split="train", split="train_extra"'
                              ' or split="val"')
 
-        if target_type not in ['instance', 'semantic', 'polygon', 'color']:
-            raise ValueError('Invalid value for "target_type"! Please use target_type="instance",'
-                             ' target_type="semantic", target_type="polygon" or target_type="color"')
+        if not isinstance(target_type, list):
+            self.target_type = [target_type]
+
+        if not all(t in ['instance', 'semantic', 'polygon', 'color'] for t in self.target_type):
+            raise ValueError('Invalid value for "target_type"! Valid values are: "instance", "semantic", "polygon"'
+                             ' or "color"')
 
         if not os.path.isdir(self.images_dir) or not os.path.isdir(self.targets_dir):
             raise RuntimeError('Dataset not found or incomplete. Please make sure all required folders for the'
@@ -56,27 +86,36 @@ def __init__(self, root, split='train', mode='gtFine', target_type='instance',
             img_dir = os.path.join(self.images_dir, city)
             target_dir = os.path.join(self.targets_dir, city)
             for file_name in os.listdir(img_dir):
-                target_name = '{}_{}'.format(file_name.split('_leftImg8bit')[0],
-                                             self._get_target_suffix(self.mode, self.target_type))
+                target_types = []
+                for t in self.target_type:
+                    target_name = '{}_{}'.format(file_name.split('_leftImg8bit')[0],
+                                                 self._get_target_suffix(self.mode, t))
+                    target_types.append(os.path.join(target_dir, target_name))
 
                 self.images.append(os.path.join(img_dir, file_name))
-                self.targets.append(os.path.join(target_dir, target_name))
+                self.targets.append(target_types)
 
     def __getitem__(self, index):
         """
         Args:
             index (int): Index
         Returns:
-            tuple: (image, target) where target is a json object if target_type="polygon",
-            otherwise the image segmentation.
+            tuple: (image, target) where target is a tuple of all target types if target_type is a list with more
+            than one item. Otherwise target is a json object if target_type="polygon", else the image segmentation.
         """
 
         image = Image.open(self.images[index]).convert('RGB')
 
-        if self.target_type == 'polygon':
-            target = self._load_json(self.targets[index])
-        else:
-            target = Image.open(self.targets[index])
+        targets = []
+        for i, t in enumerate(self.target_type):
+            if t == 'polygon':
+                target = self._load_json(self.targets[index][i])
+            else:
+                target = Image.open(self.targets[index][i])
+
+            targets.append(target)
+
+        target = tuple(targets) if len(targets) > 1 else targets[0]
 
         if self.transform:
             image = self.transform(image)