in img.imdecode,when py3 check buf param,if it is str,convert it to b…

…ytes.

python/mxnet/image/image.py

@@ -25,6 +25,8 @@
 import random
 import logging
 import json
+import sys
+
 import numpy as np
 
 try:
@@ -133,6 +135,9 @@ def imdecode(buf, *args, **kwargs):
     """
     if not isinstance(buf, nd.NDArray):
         buf = nd.array(np.frombuffer(buf, dtype=np.uint8), dtype=np.uint8)
+    if sys.version_info[0] == 3:
+        if isinstance(buf, str):
+            buf = bytes(buf)
     return _internal._cvimdecode(buf, *args, **kwargs)