1) Dictionaries have a method called get that takes a key and a default value.
LookupError is a built-in exception used to indicate that a lookup operation failed.
raise LookupError(‘value does not appear in the dictionary‘)
A dictionary is implemented using a hashtable and that means that the keys have to be hashable. A hash is a function that takes a value (of any kind) and returns an integer. Dictionaries use these integers, called hash values, to store and look up key-value pairs.
本文出自 “7773725” 博客，请务必保留此出处http://7783725.blog.51cto.com/7773725/1763854
原文：http://7783725.blog.51cto.com/7773725/1763854