docstr: Build the query RL for the quandl WIKI metadata.
          
docstr_tok: ["Build","the","query","RL","for","the","quandl","WIKI","metadata","."]
code: def _format_metadata_url(self, api_key, page_number):
      """Build the query RL for the quandl WIKI metadata."""
      query_params = [
          ("per_page", "100"),
          ("sort_by", "id"),
          ("page", str(page_number)),
          ("database_code", "WIKI"),
      ]
      if api_key is not None:
          query_params = [("api_key", api_key)] + query_params
  
      return "https://www.quandl.com/api/v3/datasets.csv?" + 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 12 for calling the QuandlBundle obj's underlying member method code with example usage: obj._format_metadata_url(api_key, page_number) and returns: unknown