General purpose zset union/intersect code (probably too meta)

sets.py

#!/usr/bin/env python
import lib.akn.config as cfg 
cfg.init(False)
from lib.akn.exceptions import CallError

def __zset_fetch(bind_pairs, start=0, end=29, count=False,
    reverse=True, ids_only=False, operator="union", **kwargs):
  """General purpose tool for doing zset traversal in redis without abusing
  local memory too much. To call it, you send in pairs consisting of
    * a string representing a zset's key
    * an optional variable to interpolate into the first element of the pair

  If there is more than 1 pair, then the operator kwarg comes into play.
  Currently, union and intersection are supported via the native ZUNIONSTORE and
  ZINTERSTORE redis commands, respectively.
  """
  post_ids = []
  keys = []

  print "zset featch on pairs:", bind_pairs

  for pair in bind_pairs:
    if len(pair) == 1:
      by_what = pair[0]
    elif len(pair) == 2:
      by_what, some_id = pair
    else:
      raise CallError('each element of bind_pairs must be a 1 or 2 tuple')

    if by_what == "featured":
      keys.append("featured:by_date_created")
    elif by_what == "usage_type":
      keys.append("usage_type:%s:by_date_created" % some_id)
    elif by_what == "media_type":
      keys.append("media_type:%s:by_date_created" % some_id)
    elif by_what == "spotlight":
      keys.append("user:%s:spotlight_posts" % some_id)
    elif by_what == 'hashtag':
      keys.append("hashtag:%s:posts" % some_id)
    else:
      raise CallError('cannot get posts by %s' % by_what)


  with cfg.main_db.connection() as c:
    key = None
    if len(keys) == 1:
      key = keys[0]
      print "KEY derp", key 
    else:
      # we need to do some basic set operations before proceeding
      print "operator", operator
      if operator == "intersect":
        key = "TEMP_INTERSECT_ZSET"
        c.zinterstore(key, keys)
      elif operator == "union":
        key = "TEMP_UNION_ZSET"
        c.zunionstore(key, keys)

    if count:
      return c.zcard(key)

    print "fetching %s:%s of %s reverse:%s" % (start, end, key, reverse)
    if reverse:
      post_ids = c.zrevrange(key, start, end)
    else:
      post_ids = c.zrange(key, start, end)
  return post_ids

print __zset_fetch(
    (
      ("hashtag", "science"),
      ("usage_type", "rekeep")
    ), operator="intersect", ids_only=True)

mget_rekeeps_by_hashtags = lambda hashtags, **kwargs: __zset_fetch(
    [("usage_type", "rekeep"),] + [("hashtag", ht) for ht in hashtags],
    operator="intersect", **kwargs)

print mget_rekeeps_by_hashtags(['science', 'derp'])