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","."]
docstr: Cost parameter is the cost of a trade per-dollar. 0.0015
  on $1 million means $1,500 commission (=1M * 0.0015)
docstr_tok: ["Cost","parameter","is","the","cost","of","a","trade","per-dollar",".","0.0015","on","$","1","million","means","$","1,500","commission","(","=1M","*","0.0015",")"]
code: def __init__(self, cost=DEFAULT_PER_DOLLAR_COST):
      """
      Cost parameter is the cost of a trade per-dollar. 0.0015
      on $1 million means $1,500 commission (=1M * 0.0015)
      """
      self.cost_per_dollar = float(cost)
  
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 1 to create a new PerDollar object from inherited base classes: EquityCommissionModel with example: obj = PerDollar(cost)