fix a bug described in issue #488

Author: KovenYu

torchvision/transforms/transforms.py

@@ -367,7 +367,8 @@ class RandomCrop(object):
         padding (int or sequence, optional): Optional padding on each border
             of the image. Default is 0, i.e no padding. If a sequence of length
             4 is provided, it is used to pad left, top, right, bottom borders
-            respectively.
+            respectively. If a sequence of length 2 is provided, it is used to pad
+            top/bottom, left/right.
         pad_if_needed (boolean): It will pad the image if smaller than the
             desired size to avoid raising an exception.
     """
@@ -377,6 +378,13 @@ def __init__(self, size, padding=0, pad_if_needed=False):
             self.size = (int(size), int(size))
         else:
             self.size = size
+
+        if isinstance(padding, numbers.Number):
+            padding = (int(padding), int(padding), int(padding), int(padding))
+        elif len(padding) == 2:
+            padding = (int(padding[1]), int(padding[0]), int(padding[1]), int(padding[0]))
+        elif len(padding) != 4:
+            assert False, "The length of padding must be either 2 or 4, but got {}.".format(len(padding))
         self.padding = padding
         self.pad_if_needed = pad_if_needed
 
@@ -408,7 +416,7 @@ def __call__(self, img):
         Returns:
             PIL Image: Cropped image.
         """
-        if self.padding > 0:
+        if any(np.array(self.padding) > 0):
             img = F.pad(img, self.padding)
 
         # pad the width if needed