How is the efficiency of key-value lookup in a Python dictionary determined?

In Python, a dictionary (dict) is implemented based on a hash table. The efficiency of searching for a value by key is determined by the time it takes to compute the hash function and resolve collisions. On average, the search operation is performed in O(1) time, which is constant time. However, in the worst case (with a large number of collisions), the time can degrade to O(n). Therefore, the efficiency depends on the quality of the hash function and the distribution of keys.