Python hash() function is a built-in function and returns the hash value of an object if it has one. The hash value is an integer which is used to quickly compare dictionary keys while looking at a dictionary.
Syntax of Python hash() method:
Syntax : hash(obj)
Parameters : obj : The object which we need to convert into hash.
Returns : Returns the hashed value if possible.
Properties of hash() function
- Objects hashed using hash() are irreversible, leading to loss of information.
- hash() returns hashed value only for immutable objects, hence can be used as an indicator to check for mutable/immutable objects.
Python hash() methods Examples
Example 1: Demonstrating working of hash()
Python3
# Python 3 code to demonstrate# working of hash()# initializing objectsint_val = 4str_val = 'Lazyroar'flt_val = 24.56# Printing the hash values.# Notice Integer value doesn't change# You'll 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))) |
Output:
The integer hash value is : 4 The string hash value is : -5570917502994512005 The float hash value is : 1291272085159665688
Example 2: Demonstrating property of hash()
Python3
# Python 3 code to demonstrate# property of hash()# initializing objects# tuple are immutabletuple_val = (1, 2, 3, 4, 5)# list are mutablelist_val = [1, 2, 3, 4, 5]# Printing the hash values.# Notice exception when trying# to convert mutable objectprint("The tuple hash value is : " + str(hash(tuple_val)))print("The list hash value is : " + str(hash(list_val))) |
Output:
The tuple hash value is : 8315274433719620810
Exceptions :
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'
Example 3: hash() for immutable tuple object
Python3
# hash() for immutable tuple objectvar = ('G','E','E','K')print(hash(var)) |
Output:
5434435027328283763
Example 4: hash() on the mutable object
hash() method used by one immutable object, if we use this on a mutable object like list, set, dictionaries then it will generate an error.
Python3
l = [1, 2, 3, 4]print(hash(l)) |
Output:
TypeError: unhashable type: 'list'
Example 5: hash() on a Custom Object
Here we will override the __hash()__ methods to call the hash(), and __eq__() method will check the equality of the two custom objects.
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 hashemp_copy = Emp('Ragav', 12)print("The hash is: %d" % hash(emp_copy)) |
Output:
The hash is: -674930604243231063 The hash is: -674930604243231063
