class_docstr: For each gradient tensor, summary its histogram and add it to moving
  summaries.
class_docstr_tok: ["For","each","gradient","tensor",",","summary","its","histogram","and","add","it","to","moving","summaries","."]
docstr: Args:
      regex(str): same as in :class:`MapGradient`.
      collections (list[str]): list of collection names
docstr_tok: ["Args",":","regex","(","str",")",":","same","as","in",":","class",":","`","MapGradient","`",".","collections","(","list","[","str","]",")",":","list","of","collection","names"]
code: def __init__(self, regex=".*", collections=None):
      """
      Args:
          regex(str): same as in :class:`MapGradient`.
          collections (list[str]): list of collection names
      """
      super(SummaryGradient, self).__init__(self._mapper, regex)
      self._coll = collections
  
imports: import inspect
  import re
  from abc import ABCMeta, abstractmethod
  import six
  import tensorflow
  from ..compat import tfv1
  from ..utils import logger
  from .summary import add_moving_summary
  from .symbolic_functions import print_stat, rms
label_desc: Use image node_id 1 to create a new SummaryGradient object from inherited base classes: MapGradient with example: obj = SummaryGradient(regex, collections)