class_docstr: Create a new system. All systems are stored in
  ``System.systems``. Duplicate names are not allowed.
  
  Parameters
  ----------
  name : str
      The system name.
  longentry : str
      Name of the conditional feature for a long entry.
  shortentry : str, optional
      Name of the conditional feature for a short entry.
  longexit : str, optional
      Name of the conditional feature for a long exit.
  shortexit : str, optional
      Name of the conditional feature for a short exit.
  holdperiod : int, optional
      Holding period of a position.
  scale : bool, optional
      Add to a position for a signal in the same direction.
  
  Attributes
  ----------
  systems : dict
      Class variable for storing all known systems
  
  Examples
  --------
  
  >>> System('closer', hc, lc)
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code: def __str__(self):
      return self.name
  
imports: from alphapy.frame import Frame
  from alphapy.frame import frame_name
  from alphapy.frame import read_frame
  from alphapy.frame import write_frame
  from alphapy.globals import Orders
  from alphapy.globals import BSEP, SSEP
  from alphapy.variables import vexec
  from alphapy.space import Space
  from alphapy.portfolio import Trade
  from alphapy.utilities import most_recent_file
  import logging
  import numbers
  import pandas
  from pandas import DataFrame
label_desc: Use image node_id 3 for calling the System obj's underlying member method code with example usage: obj.__str__() and returns: self