class_docstr: Calculates a commission for a transaction based on a per dollar cost.
  
  Parameters
  ----------
  cost : float
      The flat amount of commissions paid per dollar of equities traded.
class_docstr_tok: ["Calculates","a","commission","for","a","transaction","based","on","a","per","dollar","cost",".","Parameters","--","--","--","--","--","cost",":","float","The","flat","amount","of","commissions","paid","per","dollar","of","equities","traded","."]
code: def __repr__(self):
      return "{class_name}(cost_per_dollar={cost})".format(
          class_name=self.__class__.__name__, cost=self.cost_per_dollar
      )
  
imports: from abc import abstractmethod
  from collections import defaultdict
  from six import with_metaclass
  from toolz import merge
  from catalyst.assets import Equity, Future
  from catalyst.finance.constants import FUTURE_EXCHANGE_FEES_BY_SYMBOL
  from catalyst.finance.shared import AllowedAssetMarker, FinancialModelMeta
  from catalyst.utils.dummy import DummyMapping
label_desc: Use image node_id 2 for calling the PerDollar obj's underlying member method code with example usage: obj.__repr__() and returns: str