Python hash() 方法

Python hash()函数是一个内置函数，如果对象有哈希值，则返回该对象的哈希值。哈希值是一个整数，用于在查看字典时快速比较字典键。

Python hash() 方法的语法：

Syntax : hash(obj)

Parameters : obj : The object which we need to convert into hash.

Returns : Returns the hashed value if possible.

编程需要懂一点英语

hash()函数的属性

使用 hash() 散列的对象是不可逆的，导致信息丢失。
hash() 仅返回不可变对象的哈希值，因此可用作检查可变/不可变对象的指标。

Python hash() 方法示例

示例 1：演示 hash() 的工作原理

Python3

# Python 3 code to demonstrate
# working of hash()
 
# initializing objects
int_val = 4
str_val = 'GeeksforGeeks'
flt_val = 24.56
 
# Printing the hash values.
# Notice Integer value doesn't change
# You'l have answer later in article.
print("The integer hash value is : " + str(hash(int_val)))
print("The string hash value is : " + str(hash(str_val)))
print("The float hash value is : " + str(hash(flt_val)))

Python3

# Python 3 code to demonstrate
# property of hash()
 
# initializing objects
# tuple are immutable
tuple_val = (1, 2, 3, 4, 5)
 
# list are mutable
list_val = [1, 2, 3, 4, 5]
 
# Printing the hash values.
# Notice exception when trying
# to convert mutable object
print("The tuple hash value is : " + str(hash(tuple_val)))
print("The list hash value is : " + str(hash(list_val)))

Python3

# hash() for immutable tuple object
var = ('G','E','E','K')
 
print(hash(var))

Python3

l = [1, 2, 3, 4]
print(hash(l))

Python3

class Emp:
    def __init__(self, emp_name, id):
        self.emp_name = emp_name
        self.id = id
 
    def __eq__(self, other):
       
        # Equality Comparison between two objects
        return self.emp_name == other.emp_name and self.id == other.id
 
    def __hash__(self):
       
        # hash(custom_object)
        return hash((self.emp_name, self.id))
 
emp = Emp('Ragav', 12)
print("The hash is: %d" % hash(emp))
 
# We'll check if two objects with the same
# attribute values have the same hash
emp_copy = Emp('Ragav', 12)
print("The hash is: %d" % hash(emp_copy))

输出：

The integer hash value is : 4
The string hash value is : -5570917502994512005
The float hash value is : 1291272085159665688

示例 2：演示 hash() 的属性

Python3

# Python 3 code to demonstrate
# property of hash()
 
# initializing objects
# tuple are immutable
tuple_val = (1, 2, 3, 4, 5)
 
# list are mutable
list_val = [1, 2, 3, 4, 5]
 
# Printing the hash values.
# Notice exception when trying
# to convert mutable object
print("The tuple hash value is : " + str(hash(tuple_val)))
print("The list hash value is : " + str(hash(list_val)))

输出：

The tuple hash value is : 8315274433719620810

例外：

Traceback (most recent call last):
  File "/home/eb7e39084e3d151114ce5ed3e43babb8.py", line 15, in 
    print ("The list hash value is : " + str(hash(list_val)))
TypeError: unhashable type: 'list'

示例 3：不可变元组对象的 hash()

Python3

# hash() for immutable tuple object
var = ('G','E','E','K')
 
print(hash(var))

输出：

5434435027328283763

示例 4：可变对象上的 hash()

用于不可变对象的 hash() 方法，如果我们在列表、集合、字典等可变对象上使用它，则会产生错误。

Python3

l = [1, 2, 3, 4]
print(hash(l))

输出：

TypeError: unhashable type: 'list'

示例 5：自定义对象上的 hash()

这里我们将重写 __hash()__ 方法来调用 hash()，而 __eq__() 方法将检查两个自定义对象的相等性。

Python3

class Emp:
    def __init__(self, emp_name, id):
        self.emp_name = emp_name
        self.id = id
 
    def __eq__(self, other):
       
        # Equality Comparison between two objects
        return self.emp_name == other.emp_name and self.id == other.id
 
    def __hash__(self):
       
        # hash(custom_object)
        return hash((self.emp_name, self.id))
 
emp = Emp('Ragav', 12)
print("The hash is: %d" % hash(emp))
 
# We'll check if two objects with the same
# attribute values have the same hash
emp_copy = Emp('Ragav', 12)
print("The hash is: %d" % hash(emp_copy))

输出：

The hash is: -674930604243231063
The hash is: -674930604243231063