code: def to_btc(ccy, value, api_code=None):
      
      
      res = 'tobtc?currency={0}&value={1}'.format(ccy, value)
      if api_code is not None:
          res += '&api_code=' + api_code
      return float(util.call_api(res))
docs: Call the 'tobtc' method and convert x value in the provided currency to BTC.
      
      :param str ccy: currency code
      :param float value: value to convert
      :param str api_code: Blockchain.info API code
      :return: the value in BTC