How does the dictionary work under the hood in Python?

In Python, a dictionary (dict) is implemented as a hash table with open addressing and collision resolution through probing (open addressing with linear probing or a similar method).

Main points:

• Keys are hashed using the built-in hash() function, and the result is used to determine the index in the array.
• When a collision occurs (when two keys hash to the same index), the search for the next free cell proceeds according to a specific strategy (e.g., linear or double probing).
• The dictionary dynamically expands when a certain load factor is reached to maintain operational efficiency.
• To optimize, the dictionary stores key-value pairs in an array, along with a special marker for deleted elements.

This provides amortized access, insertion, and deletion times close to O(1).

Example:

my_dict = {}
my_dict['key'] = 'value'  # Hashes 'key', finds index, inserts value
value = my_dict.get('key')  # Fast access via hash

Thus, a dictionary in Python is a highly efficient data structure optimized for fast access and dynamic modification.