英文文档：
hash(object)Return the hash value of the object (if it has one). Hash values are integers. They are used to quickly compare dictionary keys during a dictionary lookup. Numeric values that compare equal have the same hash value (even if they are of different types, as is the case for 1 and 1.0).
说明：
1. 返回对象的哈希值，用整数表示。哈希值在字典查找时，可用于快速比较键的值。
>>> hash('good good study')
1032709256
2. 相等的数值，即使类型不一致，计算的哈希值是一样的。
>>> 1.0 == 1
True
>>> hash(1.0)
1
>>> hash(1)
1
>>> hash(1.0000)
1