class_docstr: Support for `Blaze <blaze.pydata.org>`_ ``Data`` objects.
  
  Only numeric indices to columns are supported.
  
  Note:
  
    - The ``dataname`` parameter is a blaze ``Data`` object
  
    - A negative value in any of the parameters for the Data lines
      indicates it's not present in the DataFrame
      it is
class_docstr_tok: ["Support","for","`","Blaze","<","blaze.pydata.org",">","`","_","``","Data","``","objects",".","Only","numeric","indices","to","columns","are","supported",".","Note",":","-","The","``","dataname","``","parameter","is","a","blaze","``","Data","``","object","-","A","negative","value","in","any","of","the","parameters","for","the","Data","lines","indicates","it","'s","not","present","in","the","DataFrame","it","is"]
code: def _load(self):
      try:
          row = next(self._rows)
      except StopIteration:
          return False
  
      # Set the standard datafields - except for datetime
      for datafield in self.datafields[1:]:
          # get the column index
          colidx = getattr(self.params, datafield)
  
          if colidx < 0:
              # column not present -- skip
              continue
  
          # get the line to be set
          line = getattr(self.lines, datafield)
          line[0] = row[colidx]
  
      # datetime - assumed blaze always serves a native datetime.datetime
      colidx = getattr(self.params, self.datafields[0])
      dt = row[colidx]
      dtnum = date2num(dt)
  
      # get the line to be set
      line = getattr(self.lines, self.datafields[0])
      line[0] = dtnum
  
      # Done ... return
      return True
  
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from backtrader import date2num
  import backtrader.feed
label_desc: Use image node_id 2 for calling the BlazeData obj's underlying member method code with example usage: obj._load() and returns: True, False