class_docstr: The system wide writer class.
  
  It can be parametrized with:
  
    - ``out`` (default: ``sys.stdout``): output stream to write to
  
      If a string is passed a filename with the content of the parameter will
      be used.
  
      If you wish to run with ``sys.stdout`` while doing multiprocess optimization, leave it as ``None``, which will
      automatically initiate ``sys.stdout`` on the child processes.
  
    - ``close_out``  (default: ``False``)
  
      If ``out`` is a stream whether it has to be explicitly closed by the
      writer
  
    - ``csv`` (default: ``False``)
  
      If a csv stream of the data feeds, strategies, observers and indicators
      has to be written to the stream during execution
  
      Which objects actually go into the csv stream can be controlled with
      the ``csv`` attribute of each object (defaults to ``True`` for ``data
      feeds`` and ``observers`` / False for ``indicators``)
  
    - ``csv_filternan`` (default: ``True``) whether ``nan`` values have to be
      purged out of the csv stream (replaced by an empty field)
  
    - ``csv_counter`` (default: ``True``) if the writer shall keep and print
      out a counter of the lines actually output
  
    - ``indent`` (default: ``2``) indentation spaces for each level
  
    - ``separators`` (default: ``['=', '-', '+', '*', '.', '~', '"', '^',
      '#']``)
  
      Characters used for line separators across section/sub(sub)sections
  
    - ``seplen`` (default: ``79``)
  
      total length of a line separator including indentation
  
    - ``rounding`` (default: ``None``)
  
      Number of decimal places to round floats down to. With ``None`` no
      rounding is performed
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code: def writeiterable(self, iterable, func=None, counter=""):
      if self.p.csv_counter:
          iterable = itertools.chain([counter], iterable)
  
      if func is not None:
          iterable = map(lambda x: func(x), iterable)
  
      line = self.p.csvsep.join(iterable)
      self.writeline(line)
  
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import collections
  import io
  import itertools
  import sys
  import backtrader
  from backtrader.utils.py3 import map, with_metaclass, string_types, integer_types
label_desc: Use image node_id 8 for calling the WriterFile obj's underlying member method code with example usage: obj.writeiterable(iterable, func, counter) without return types