Can you explain what a hash table data structure is and how it works?

A hash table is a data structure that stores key-value pairs and provides very fast access to data by key. It works using a hash function that transforms the key into an array index where the value is stored.

Working principle:

1. The key is passed to the hash function.
2. The hash function returns an index in the array.
3. The value or a list of values (in case of collisions) is stored at this index.

Collisions are situations where different keys produce the same index. Methods to handle collisions include chaining (linked lists) or open addressing.

Example in Python using a dictionary (built-in hash table):

my_dict = {}
my_dict['apple'] = 5
my_dict['banana'] = 3
print(my_dict['apple'])  # Outputs 5

Dictionaries in Python are implemented based on hash tables and provide quick access to elements.