docstr: Build a query URL for a quandl WIKI dataset.
docstr_tok: ["Build","a","query","URL","for","a","quandl","WIKI","dataset","."]
code: def _format_wiki_url(
      self, api_key, symbol, start_date, end_date, data_frequency
  ):
      """
      Build a query URL for a quandl WIKI dataset.
      """
      query_params = [
          ("start_date", start_date.strftime("%Y-%m-%d")),
          ("end_date", end_date.strftime("%Y-%m-%d")),
          ("order", "asc"),
      ]
      if api_key is not None:
          query_params = [("api_key", api_key)] + query_params
  
      return (
          "https://www.quandl.com/api/v3/datasets/WIKI/"
          "{symbol}.csv?{query}".format(
              symbol=symbol,
              query=urlencode(query_params),
          )
      )
  
imports: from datetime import datetime
  import pandas
  from six.moves.urllib.parse import urlencode
  from catalyst.data.bundles.core import register_bundle
  from catalyst.data.bundles.base_pricing import BaseEquityPricingBundle
  from catalyst.utils.memoize import lazyval
  from logbook import Logger
  from catalyst.constants import LOG_LEVEL
  from catalyst.utils.calendars import register_calendar_alias
label_desc: Use image node_id 13 for calling the QuandlBundle obj's underlying member method code with example usage: obj._format_wiki_url(api_key, symbol, start_date, end_date, data_frequency) and returns: str