class_docstr: Calculates a commission for a transaction based on a per share cost with
  an optional minimum cost per trade.
  
  Parameters
  ----------
  cost : float, optional
      The amount of commissions paid per share traded. Default is one tenth
      of a cent per share.
  min_trade_cost : float, optional
      The minimum amount of commissions paid per trade. Default is no
      minimum.
  
  Notes
  -----
  This is zipline's default commission model for equities.
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code: def __repr__(self):
      return (
          "{class_name}(cost_per_share={cost_per_share}, "
          "min_trade_cost={min_trade_cost})".format(
              class_name=self.__class__.__name__,
              cost_per_share=self.cost_per_share,
              min_trade_cost=self.min_trade_cost,
          )
      )
  
imports: from abc import abstractmethod
  from collections import defaultdict
  from six import with_metaclass
  from toolz import merge
  from zipline.assets import Equity, Future
  from zipline.finance.constants import FUTURE_EXCHANGE_FEES_BY_SYMBOL
  from zipline.finance.shared import AllowedAssetMarker, FinancialModelMeta
  from zipline.utils.dummy import DummyMapping
label_desc: Use image node_id 2 for calling the PerShare obj's underlying member method code with example usage: obj.__repr__() and returns: str