docs: def to_contracts(instruments, prices, multipliers, desired_ccy=None,
                   instr_fx=None, fx_rates=None, rounder=None):
      """
      Convert notional amount of tradeable instruments to number of instrument
      contracts, rounding to nearest integer number of contracts.
  
      Parameters
      ----------
      instruments: pandas.Series
          Series of instrument holdings. Index is instrument name and values are
          notional amount on instrument.
      prices: pandas.Series
          Series of instrument prices. Index is instrument name and values are
          instrument prices. prices.index should be a superset of
          instruments.index
      multipliers: pandas.Series
          Series of instrument multipliers. Index is instrument name and
          values are the multiplier associated with the contract.
          multipliers.index should be a superset of instruments.index
      desired_ccy: str
          Three letter string representing desired currency to convert notional
          values to, e.g. 'USD'. If None is given currency conversion is ignored.
      instr_fx: pandas.Series
          Series of instrument fx denominations. Index is instrument name and
          values are three letter strings representing the currency the
          instrument is denominated in. instr_fx.index should match prices.index
      fx_rates: pandas.Series
          Series of fx rates used for conversion to desired_ccy. Index is strings
          representing the FX pair, e.g. 'AUDUSD' or 'USDCAD'. Values are the
          corresponding exchange rates.
      rounder: function
          Function to round pd.Series contracts to integers, if None default
          pd.Series.round is used.
  
      Returns
      -------
      pandas.Series of contract numbers of instruments with Index of instruments
      names
      """
      contracts = _instr_conv(instruments, prices, multipliers, False,
                              desired_ccy, instr_fx, fx_rates)
      if rounder is None:
          rounder = pd.Series.round
  
      contracts = rounder(contracts)
      contracts = contracts.astype(int)
      return contracts