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Updated on 2025-03-03

Detailed explanation of the secret of hash value of hash function in Python

Preface

In Python,hash()Functions are methods used to obtain the hash value of an object. This article will discuss in depthhash()The usage, working principle and common application scenarios of functions are convenient for everyone to better understand and apply this function.

What is the hash() function?

hash()Functions are a built-in function in Python that gets the hash value of an object. A hash value is a fixed-length integer that uniquely identifies an object. Objects with the same content will have the same hash value, and objects with different content will have different hash value.

hash()The basic syntax of a function is as follows:

hash(object)

in,objectIt is an object to obtain the hash value, which can be an immutable object such as numbers, strings, and tuples.

The basic usage of hash() function

Let's take a look at some firsthash()Basic usage of functions.

1. Get the hash value of the number

print(hash(42))      # 42
print(hash(3.14))    # 3430007490030933

In this example, usehash()The function gets the hash values ​​of integers and floating point numbers.

2. Get the hash value of the string

print(hash("hello"))  # -1556557540336409064
print(hash("world"))  # 7705868722141818761

In this example, usehash()The function gets the hash value of two strings.

3. Get the hash value of the tuple

print(hash((1, 2, 3)))   # 2528502973977326415
print(hash((4, 5, 6)))   # 3550055125485641917

In this example, usehash()The function gets the hash value of two tuples.

Common application scenarios of hash() function

hash()Functions have many application scenarios in Python programming, and the following are some common uses:

1. Dictionary keys

hash()Functions are often used in dictionary keys, and key-value pairs are quickly positioned through the hash value of an object.

my_dict = {"apple": 42, "banana": 17, "orange": 33}
print(my_dict[hash("apple")])  # 42

In this example, usehash()Functions string"apple"Convert to a hash value and then use the hash value to get the corresponding value in the dictionary.

2. Elements of the collection

hash()Functions are also often used for collection elements, and elements are quickly positioned through the hash value of the object.

my_set = {1, 2, 3, 4, 5}
print(hash(3) in my_set)  # True

In this example, usehash()Functions determine integers3Whether it is in the collection.

3. Customize the hash value of the object

You can rewrite the object's__hash__()Methods customize the hash value of the object.

class MyClass:
    def __init__(self, value):
         = value
    
    def __hash__(self):
        return hash()

obj = MyClass(42)
print(hash(obj))  # 42

In this example, a custom class is definedMyClass, and rewritten__hash__()Method, such that the hash value of the object is equal to its value.

4. Storage and search of hash tables

hash()Functions are widely used in hash table data structures and are used to store and find elements.

# Create a hash tablehash_table = {}

# Insert elementhash_table[hash("apple")] = 42
hash_table[hash("banana")] = 17
hash_table[hash("orange")] = 33

# Find elementsprint(hash_table[hash("apple")])  # 42

In this example, usehash()The function converts a string to a hash value and stores the element in a hash table, and then uses the hash value to quickly find the element.

5. Safe hashing algorithm

hash()Functions also have important applications in cryptography and can be used to generate secure hashing algorithms.

import hashlib

password = "password123"
hashed_password = hashlib.sha256(()).hexdigest()
print(hashed_password)

In this example, usehashlibModularsha256()The method hashs the password to generate a safe hash value.

6. Data sharding

hash()Functions are often used in distributed systems for data sharding, and data is scattered and stored on different nodes according to the hash value of the object.

#Storage data according to hash valuenum_shards = 4
data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
shards = [[] for _ in range(num_shards)]

for item in data:
    shard_index = hash(item) % num_shards
    shards[shard_index].append(item)

print(shards)

In this example, data is sliced ​​on different nodes according to its hash value, enabling distributed storage of data.

Make some additional information:

When hash() is used on an object, the result obtained has nothing to do with the content of the object, but only with the object's id(), that is, the memory address.

class foo(object):
    def __init__(self,x):
        =x
    def get_x(self):
        return 
    def set_x(self,x):
        =x

test=foo(1)
print(hash(test),test.get_x(),id(test))
test.set_x(0)
print(hash(test),test.get_x(),id(test))

Output:

3518817 1 56301072
3518817 0 56301072

Summarize

hash()Functions are a very useful built-in function in Python to get the hash value of an object. By rational applicationhash()Functions can realize the rapid storage, search and sharding of data, and improve the efficiency and security of the program. I hope the examples and explanations provided in this article can help you better understand and apply them.hash()Functions play a greater role in actual development.

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