docs: def rename_collection(db, collection, new_name):
      '''
      Renames a MongoDB collection.
  
      Arguments:
  
          db (Database): A pymongo Database object. Can be obtained
              with ``get_db``.
  
          collection (str): Name of the collection to be renamed.
  
          new_name (str, func): ``new_name`` can be one of two things::
  
              1. The new collection name, as a string.
              2. A function which, when passed the current collection name,
                  returns the new collection name. If the function
                  returns an empty string, the collection will not be
                  renamed.
      '''
      if hasattr(new_name, '__call__'):
          _new = new_name(collection)
          if _new == '':
              return
      else:
          _new = new_name
      c = db[collection]
      c.rename(_new)