How Can You Implement a Bidirectional Hash Table in Python?

Bi-Directional Hash Table Implementation with Bidict Class

Bidirectional hash tables provide the ability to index by both keys and values within the same data structure. Python's native dictionary is a valuable data structure for one-way mapping, but it falls short when it comes to bidirectional lookup. This article presents an efficient way to implement a bidirectional hash table in Python.

Implementation Details

The heart of the implementation is the bidict class, which extends Python's standard dictionary. This class maintains two dictionaries: one for standard key-value mapping and another, the inverse dictionary, for value-key mapping.

Key Features

The bidict class offers several notable features:

• Auto-updating inverse directory: When the standard dictionary is modified (via item addition, modification, or deletion), the inverse dictionary updates itself automatically.
• Lists of keys for same value: Unlike some other bidirectional dict implementations, bidict allows multiple keys to have the same value.
• Efficient lookup: Retrieval of keys or values is performed in constant time, leveraging the native Python dictionary implementation.

Usage Example

To demonstrate its functionality, let's create a bidict and manipulate it:

<code class="python">import numpy as np
bd = bidict(zip(['a', 'b'], np.random.randint(2, size=2)))
print(bd)  # {'a': 1, 'b': 0}
print(bd.inverse)  # {1: ['a'], 0: ['b']}</code>

We can modify the value for key 'a':

<code class="python">bd['a'] = 0
print(bd)  # {'b': 0, 'a': 0}
print(bd.inverse)  # {0: ['b', 'a']}</code>

Note that the inverse dictionary automatically updates to reflect the change. We can also delete items from the dictionary:

<code class="python">del bd['a']
print(bd)  # {'b': 0}
print(bd.inverse)  # {0: ['b']}</code>

Again, the inverse dictionary seamlessly adjusts to the deletion.

In conclusion, the bidict class provides an efficient and convenient implementation of a bidirectional hash table in Python, offering auto-updating inverse directory, support for multiple keys with the same value, and constant-time lookup.

The above is the detailed content of How Can You Implement a Bidirectional Hash Table in Python?. For more information, please follow other related articles on the PHP Chinese website!