I use two classes to track accounts and transactions:

  class acct(object):
    # bank and brokerage account
    allacct = []

    def __init__(self, name, balance, holdings=None):
        self.name = name
        self.balance = balance
        self.holdings = holdings
        self.xferamt = 0
        self.accum = 0 # used to track cumulation ad hoc values
        acct.allacct.append(self)

    def buy(self, sec, amt, cost, day):
        rec = trans(('buy', sec, amt), -cost, day, self)
        self.balance -= cost
        if not self.holdings.has_key(sec):
            self.holdings[sec] = [0]
        self.holdings[sec][0] += amt
        self.holdings[sec].append(rec)
  ......

  class trans(object):
    # transaction record object track cash invovled in each transaction

    allrec = []

    def __init__(self, t, amt, day, where):
        try:
            self.type = t
            self.amt = amt
            self.date = date(year, month, day)
            self.where = where

            trans.allrec.append(self)
        except Exception as err:
            print t, amt, year, month, day, where
            raise err            

Then for each data line I just do any of the following:

  SOMEACCT.buy(...)
  SOMEACCT.sell(...)
  SOMEACCT.credit(...)
  SOMEACCT.debit(...)
  SOMEACCT.xfer(...)
  # classified by tax categories:
  SOMEACCT.int(...)
  SOMEACCT.div(...)
  SOMEACCT.fdiv(...)
  SOMEACCT.mint(...)
  SOMEACCT.mdiv(...)

Then it is easy to query and do computations in any way one cares to write a function to do.