class_docstr: Parses a CSV file according to the order and field presence defined by the
  parameters
  
  Specific parameters (or specific meaning):
  
    - ``dataname``: The filename to parse or a file-like object
  
    - The lines parameters (datetime, open, high ...) take numeric values
  
      A value of -1 indicates absence of that field in the CSV source
  
    - If ``time`` is present (parameter time >=0) the source contains
      separated fields for date and time, which will be combined
  
    - ``nullvalue``
  
      Value that will be used if a value which should be there is missing
      (the CSV field is empty)
  
    - ``dtformat``: Format used to parse the datetime CSV field. See the
      python strptime/strftime documentation for the format.
  
      If a numeric value is specified, it will be interpreted as follows
  
        - ``1``: The value is a Unix timestamp of type ``int`` representing
          the number of seconds since Jan 1st, 1970
  
        - ``2``: The value is a Unix timestamp of type ``float``
  
      If a **callable** is passed
  
        - it will accept a string and return a `datetime.datetime` python
          instance
  
    - ``tmformat``: Format used to parse the time CSV field if "present"
      (the default for the "time" CSV field is not to be present)
code: def start(self):
      super(GenericCSVData, self).start()
  
      self._dtstr = False
      if isinstance(self.p.dtformat, string_types):
          self._dtstr = True
      elif isinstance(self.p.dtformat, integer_types):
          idt = int(self.p.dtformat)
          if idt == 1:
              self._dtconvert = lambda x: datetime.utcfromtimestamp(
                  int(x)
              )
          elif idt == 2:
              self._dtconvert = lambda x: datetime.utcfromtimestamp(
                  float(x)
              )
  
      else:  # assume callable
          self._dtconvert = self.p.dtformat
  
file_path: backtrader/backtrader/feeds/csvgeneric.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from datetime import datetime
  import itertools
  from ..None import feed, TimeFrame
  from ..utils import date2num
  from ..utils.py3 import integer_types, string_types
label_desc: Use image node_id 1 for calling the GenericCSVData obj's underlying member method code with example usage: obj.start() without return types