class_docstr: Uses a Pandas DataFrame as the feed source, using indices into column
  names (which can be "numeric")
  
  This means that all parameters related to lines must have numeric
  values as indices into the tuples
  
  Params:
  
    - ``nocase`` (default *True*) case insensitive match of column names
  
  Note:
  
    - The ``dataname`` parameter is a Pandas DataFrame
  
    - Values possible for datetime
  
      - None: the index contains the datetime
      - -1: no index, autodetect column
      - >= 0 or string: specific colum identifier
  
    - For other lines parameters
  
      - None: column not present
      - -1: autodetect
      - >= 0 or string: specific colum identifier
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code: def start(self):
      super(PandasData, self).start()
  
      # reset the length with each start
      self._idx = -1
  
      # Transform names (valid for .ix) into indices (good for .iloc)
      if self.p.nocase:
          colnames = [x.lower() for x in self.p.dataname.columns.values]
      else:
          colnames = [x for x in self.p.dataname.columns.values]
  
      for k, v in self._colmapping.items():
          if v is None:
              continue  # special marker for datetime
          if isinstance(v, string_types):
              try:
                  if self.p.nocase:
                      v = colnames.index(v.lower())
                  else:
                      v = colnames.index(v)
              except ValueError as e:
                  defmap = getattr(self.params, k)
                  if isinstance(defmap, integer_types) and defmap < 0:
                      v = None
                  else:
                      raise e  # let user now something failed
  
          self._colmapping[k] = v
  
file_path: backtrader/backtrader/feeds/pandafeed.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from backtrader.utils.py3 import filter, string_types, integer_types
  from backtrader import date2num
  import backtrader.feed
label_desc: Use image node_id 2 for calling the PandasData obj's underlying member method code with example usage: obj.start() without return types