code: def _format_data_url(
      self, api_key, symbol, start_date, end_date, data_frequency
  ):
      period_map = {
          "daily": 86400,
      }
  
      try:
          period = period_map[data_frequency]
      except KeyError:
          return None
  
      query_params = [
          ("command", "returnChartData"),
          ("currencyPair", symbol),
          ("start", start_date.value / 10**9),
          ("end", end_date.value / 10**9),
          ("period", period),
      ]
  
      return self._format_polo_query(query_params)
  
file_path: catalyst/catalyst/data/bundles/poloniex.py
imports: import sys
  from six.moves.urllib.parse import urlencode
  import pandas
  from catalyst.data.bundles.core import register_bundle
  from catalyst.data.bundles.base_pricing import BaseCryptoPricingBundle
  from catalyst.utils.memoize import lazyval
  from catalyst.curate.poloniex import PoloniexCurator
label_desc: Use image node_id 10 for calling the PoloniexBundle obj's underlying member method code with example usage: obj._format_data_url(api_key, symbol, start_date, end_date, data_frequency) and returns: self, None