Python hash() Function

The hash() function in Python returns the hash value of an object. It is commonly used in hashing data structures like sets and dictionaries.

Syntax

hash(object)

Parameters:

• object – The input object must be immutable (like int, float, str, tuple with only hashable items).

Returns:

• An integer hash value that represents the object.

Example 1: Hashing Numbers

print(hash(42))
print(hash(-42))
print(hash(3.14))

(Output will be integer values like 42 or -42 or some number)

Example 2: Hashing Strings

print(hash("hello"))
print(hash("HELLO"))

(Will return integer hash values for each string)

Example 3: Using hash() with Tuples

print(hash((1, 2, 3)))

(Returns an integer hash)

Use Case: Why use hash()?

• To store objects in sets or as dictionary keys.
• To compare objects efficiently by their hash.
• To build data structures like hash tables.

Important Notes

• Only immutable objects can be hashed.
• Mutable types like list or dict will raise a TypeError.
• Hash values may differ across Python sessions (especially for strings).

Example 4: Unhashable Object (Throws Error)

print(hash([1, 2, 3]))  # List is mutable

TypeError: unhashable type: 'list'

Custom Hash in Classes

class MyClass:
    def __init__(self, value):
        self.value = value

    def __hash__(self):
        return hash(self.value)

obj = MyClass(100)
print(hash(obj))

(Depends on the value passed)

Interview Tip

Interviewers often ask about hash-based data structures. Understanding hash() is key to explaining how dict and set work in Python.

Summary

• hash() returns a unique integer based on the object's content.
• Used in sets, dicts, and custom objects.
• Only immutable objects can be hashed.

Practice Problem

Write a program to find and print the hash values of a string, a tuple, and an integer input from the user.

text = input("Enter a string: ")
number = int(input("Enter an integer: "))
tpl = (text, number)

print("Hash of string:", hash(text))
print("Hash of integer:", hash(number))
print("Hash of tuple:", hash(tpl))