Fix PrintData argument (#303)

It was always confusing, that most functions use `name` and
PrintData expected `label`.

tensorpack/dataflow/common.py

@@ -11,6 +11,7 @@ from collections import deque, defaultdict
 from six.moves import range, map
 from .base import DataFlow, ProxyDataFlow, RNGDataFlow
 from ..utils import logger, get_tqdm, get_rng
+from ..utils.develop import log_deprecated
 
 __all__ = ['TestDataSpeed', 'PrintData', 'BatchData', 'BatchDataByShape', 'FixedSizeData', 'MapData',
            'MapDataComponent', 'RepeatedData', 'RepeatedDataPoint', 'RandomChooseData',
@@ -614,7 +615,7 @@ class PrintData(ProxyDataFlow):
                dp 3: is ndarray of shape (9, 9) with range [-0.5585, 0.5585]
     """
 
-    def __init__(self, ds, num=1, label=""):
+    def __init__(self, ds, num=1, label=None, name=None):
         """
         Args:
             ds (DataFlow): input DataFlow.
@@ -623,7 +624,12 @@ class PrintData(ProxyDataFlow):
         """
         super(PrintData, self).__init__(ds)
         self.num = num
-        self.label = label
+
+        if label:
+            log_deprecated("PrintData(label, ...", "Use PrintData(name, ... instead.")
+            self.name = label
+        else:
+            self.name = name
 
     def _analyze_input_data(self, el, k, depth=1):
         """
@@ -676,7 +682,7 @@ class PrintData(ProxyDataFlow):
                 msg.append("datapoint %i<%i with %i components consists of" % (i, self.num, len(dummy)))
                 for k, entry in enumerate(dummy):
                     msg.append(self._analyze_input_data(entry, k))
-        label = "" if self.label is "" else " (" + self.label + ")"
+        label = "" if self.name is None else " (" + self.label + ")"
         logger.info(colored("DataFlow Info%s:" % label, 'cyan') + '\n'.join(msg))
 
         # reset again after print