code: def find_one(self, collection, selector={}):
          
          for _id, doc in self.collection_data.data.get(collection, {}).items():
              doc.update({'_id': _id})
              if selector == {}:
                  return doc
              for key, value in selector.items():
                  if key in doc and doc[key] == value:
                      return doc
          return None
docs: Return one item from a collection
  
          Arguments:
          collection - collection to search
  
          Keyword Arguments:
          selector - the query (default returns first item found)