Hash table and Python dictionary

One of the most useful Python collections is the dictionary, which is an associative data type where you can store key-data pairs. It is implemented using hash tables.

Hash table is a collection of items which are stored in such a way as to make it easy to find item. Each position of the hash table, often called a slot, can hold an item and is named by an integer value starting at 0. The mapping between an item and the slot where that item belongs in the hash table is called the hash function. A perfect hash function maps every items into a unique slot. When two items hash to the same slot, collision happens. And a systematic method, which called collision resolution, for placing the second item in the hash table must be put forward.