Under what conditions is access to an element in a dictionary performed in linear time?

Access to an element in a Python dictionary is usually achieved in amortized constant time (O(1)) thanks to the hash table. However, in the worst case, when there are many hash collisions (for example, all keys end up in the same bucket), access can degrade to linear time (O(n)), where n is the number of elements in the dictionary.

This occurs if the hash function poorly distributes keys or if an attacker deliberately chooses keys with the same hash. In such cases, searching for an element reduces to sequentially iterating through the elements in one bucket.

Thus, access to an element in the dictionary will be linear time in the case of severe hash collisions and lack of effective collision resolution.