## Hashing and Its Implementation in Python

As computers continue to become more advanced and capable of processing massive amounts of data, efficient algorithms and data structures become increasingly important. Hashing is one such technique used to quickly retrieve data from a large collection by converting it into a smaller and more compact form.

In this article, we will explore the basics of hashing and its implementation in Python.

## Definition and Importance of Hashing

Hashing is a process of converting a large amount of data into a unique and compact fixed-length value. This value, known as a hash value, can be used to represent the original data in a more efficient and accessible way.

Hashing is primarily used for fast retrieval of data from large collections since the memory required to store the hash values of the data is significantly less than the memory required to store the original data.

## The Hash Function in Python

Hash functions are at the heart of hashing. A hash function is a mathematical algorithm used to convert an input data of arbitrary length into an output data of fixed length.

In Python, we have built-in functions that perform hashing, such as the `hash()`

function that returns an integer hash value for objects.

## Reading or Accessing Data Using the Hash Function

To access data using the hash function in Python, we need to store the original data in a hash table. A hash table is a collection of key-value pairs where each key is converted into a hash value and used to store and retrieve data.

Retrieving data from a hash table using a hash function has a time complexity of O(1), which is very fast and efficient.

## Hashing Terminologies

### Understanding Hashing Terminology

Understanding the various terminologies used in hashing is essential in learning how to implement hashing in Python.

- The hash function is the algorithm used to convert data into hash values.
- The hash value is the fixed-length output of the hash function.
- A hash table is a data structure that stores key-value pairs using hash values as the keys.
- Collision occurs when two different data items are hashed into the same hash value.

## Implementing a HashMap in Python

A hash map is a data structure that uses hash values to store and retrieve data in key-value pairs. We can implement a basic hash map in Python using a custom class that defines functions for hashing, inserting, retrieving, and printing data.

## Example and Explanation of Hashing Implementation

To better understand how hashing works in Python, let’s create a custom class for hashing and walk through the functions required for implementation.

### Creating a Custom Class for Hashing

First, we can create a custom class that defines the hash function:

```
class HashMap:
def __init__(self):
self.hash_table = {}
def hash_function(self, key):
return hash(key) % 10
```

The hash table is initialized as an empty dictionary in the constructor, and the `hash_function()`

takes a key as input and returns a hash value.

### Explanation of Functions

Next, we can define the functions for inserting, retrieving, and printing data:

```
class HashMap:
def __init__(self):
self.hash_table = {}
def hash_function(self, key):
return hash(key) % 10
def set_value(self, key, value):
hash_value = self.hash_function(key)
if hash_value in self.hash_table:
self.hash_table[hash_value].append((key, value))
else:
self.hash_table[hash_value] = [(key, value)]
def get_value(self, key):
hash_value = self.hash_function(key)
if hash_value in self.hash_table:
for item in self.hash_table[hash_value]:
if item[0] == key:
return item[1]
return None
def print_table(self):
print(self.hash_table)
```

The `set_value()`

function takes a key-value pair as input, hashes the key to determine its hash value, and stores the data in the hash table. If the hash value already exists in the hash table, the function appends the new key-value pair to the existing list of pairs.

The `get_value()`

function takes a key as input, hashes it to find its hash value, and returns the corresponding value if it exists in the hash table. The `print_table()`

function simply prints the hash table.

### Instantiation and Setting of Values

We can now create an instance of the `HashMap`

class and set some values:

```
hash_map = HashMap()
hash_map.set_value('apple', 1)
hash_map.set_value('banana', 3)
hash_map.set_value('cherry', 5)
```

### Retrieving Values

We can retrieve the values for some keys as follows:

```
print(hash_map.get_value('apple'))
# Output: 1
print(hash_map.get_value('banana'))
# Output: 3
print(hash_map.get_value('cherry'))
# Output: 5
```

### Output and Conclusion

Finally, we can print the total hash table using the `print_table()`

function:

```
hash_map.print_table()
# Output: {4: [('banana', 3)], 2: [('apple', 1)], 5: [('cherry', 5)]}
```

In conclusion, hashing is a powerful technique used to efficiently store and access large amounts of data. When implemented using a hash table, retrieval of data becomes incredibly fast and efficient.

In Python, we have built-in hash functions, and we can create custom classes to implement hash maps for more complex data structures. Understanding the terminologies and functions related to hashing is essential for implementation in Python.

In summary, hashing is an important technique used to efficiently store and access large amounts of data. Through the use of hash functions and hash tables, retrieval of data becomes fast and efficient.

Python offers built-in hash functions, and custom classes can be created for more complex data structures. Understanding the terminologies and functions related to hashing is essential for its implementation in Python.

The main takeaway is that hashing is essential to improving the speed and efficiency of data retrieval on large collections, and its implementation in Python can be achieved through custom classes and built-in functions.