Index
- built_in_functions
- Python abs()
- Python all()
- Python any()
- Python ascii()
- Python bin()
- Python bool()
- Python bytearray()
- Python bytes()
- Python callable()
- Python chr()
- Python classmethod()
- Python compile()
- Python complex()
- Python delattr()
- Python dict()
- Python dir()
- Python divmod()
- Python enumerate()
- Python eval()
- Python exec()
- Python filter()
- Python float()
- Python format()
- Python frozenset()
- Python getattr()
- Python globals()
- Python hasattr()
- Python hash()
- Python help()
- Python hex()
- Python id()
- Python input()
- Python int()
- Python isinstance()
- Python issubclass()
- Python iter()
- Python len()
- Python list()
- Python locals()
- Python map()
- Python max()
- Python memoryview()
- Python min()
- Python next()
- Python object()
- Python oct()
- Python open()
- Python ord()
- Python pow()
- Python print()
- Python property()
- Python range()
- Python repr()
- Python reversed()
- Python round()
- Python set()
- Python setattr()
- Python slice()
- Python sorted()
- Python staticmethod()
- Python str()
- Python sum()
- Python super()
- Python tuple() Function
- Python type()
- Python vars()
- Python zip()
- Python __import__()
- python1compute
- Python Program to Find Hash of File
- Python Program to Find the Size (Resolution) of a Image
- Python Program to Merge Mails
- Python Program to Count the Number of Each Vowel - Source Code: Using a list and a dictionary comprehension
- Python Program to Count the Number of Each Vowel - Source Code: Using Dictionary
- Python Program to Illustrate Different Set Operations
- Python Program to Sort Words in Alphabetic Order
- Python Program to Remove Punctuations From a String
- Python Program to Multiply Two Matrices - Matrix Multiplication Using Nested List Comprehension
- Python Program to Multiply Two Matrices - Source Code: Matrix Multiplication using Nested Loop
- Python Program to Transpose a Matrix - Matrix Transpose using Nested List Comprehension
- Python Program to Transpose a Matrix - Matrix Transpose using Nested Loop
- Python Program to Add Two Matrices - Source Code: Matrix Addition using Nested List Comprehension
- Python Program to Check Whether a String is Palindrome or Not
- Python Program to Add Two Matrices - Source code: Matrix Addition using Nested Loop
- Python Program to Convert Decimal to Binary Using Recursion
- Python Program to Find Factorial of Number Using Recursion
- Python Program to Find Sum of Natural Numbers Using Recursion
- Python Program to Display Fibonacci Sequence Using Recursion
- Python Program to Display Calendar
- Python Program to Shuffle Deck of Cards
- Python Program to Make a Simple Calculator
- Python Program to Find Factors of Number
- Python Program to Find LCM - Without using GCD function
- Python Program to Find HCF or GCD - Source Code: Using Euclidean Algorithm
- Python Program to Find LCM - Source Code: Using GCD function
- Python Program to Find HCF or GCD - Source Code: Using Loops
- Python Program to Find ASCII Value of Character
- Python Program to Convert Decimal to Binary, Octal and Hexadecimal
- Python Program to Find Numbers Divisible by Another Number
- Python Program To Display Powers of 2 Using Anonymous Function
- Python Program to Find the Sum of Natural Numbers
- Python Program to Find Armstrong Number in an Interval
- Python Program to Check Armstrong Number - Source Code: Check Armstrong number of n digits
- Python Program to Check Armstrong Number - Source Code: Check Armstrong number (for 3 digits)
- Python Program to Print the Fibonacci sequence
- Python Program to Display the multiplication Table
- Python Program to Find the Factorial of a Number
- Python Program to Print all Prime Numbers in an Interval
- Python Program to Find the Largest Among Three Numbers
- Python Program to Check Prime Number
- Python Program to Check Leap Year
- Python Program to Check if a Number is Odd or Even
- Python Program to Check if a Number is Positive, Negative or 0 Source Code: Using Nested if
- Python Program to Check if a Number is Positive, Negative or 0 Source Code: Using if...elif...else
- Python Program to Convert Celsius To Fahrenheit
- Python Program to Generate a Random Number
- Python Program to Convert Kilometers to Miles
- Python Program to Swap Two Variables Source Code: Without Using Temporary Variable
- Python Program to Swap Two Variables Source Code: Using temporary variable
- Python Program to Solve Quadratic Equation
- Python Program to Calculate the Area of a Triangle
- Python Program to Find the Square Root Source code: For real or complex numbers using cmath module
- Python Program to Find the Square Root Source Code: For positive numbers using exponent **
- Python Program to Add Two Numbers By One Line
- Python Program to Add Two Numbers Source Code: Add Two Numbers Provided by The User
- Python Program to Add Two Numbers
- Python Program to Print Hello world!
- python2based
Description hash()
Python hash()
The hash() method returns the hash value of an object if it has one.
Hash values are just integers which are used to compare dictionary keys during a dictionary lookup quickly.
Internally, hash() method calls
__hash__()
method of an object which are set by default for any object. We'll look at this later.The syntax of hash() method is:
hash(object)
hash() Parameters
The hash() method takes a single parameter:
• object - the object whose hash value is to be returned (integer, string, float)
Return value from hash()
The hash() method returns the hash value of an object if it has one.
If an object has custom
__hash__()
method, it truncates the return value to the size of Py_ssize_t.Example 1: How hash() works in Python?
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# hash for integer unchanged
print('Hash for 181 is:', hash(181))
# hash for decimal
print('Hash for 181.23 is:',hash(181.23))
# hash for string
print('Hash for Python is:', hash('Python'))
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When you run the program, the output will be:
Hash for 181 is: 181
Hash for 181.23 is: 530343892119126197
Hash for Python is: 2230730083538390373
Example 2: hash() for immutable tuple object?
The hash() method only works for immutable objects as tuple.
-------------------------------------------------------------------------------------------------
# tuple of vowels
vowels = ('a', 'e', 'i', 'o', 'u')
print('The hash is:', hash(vowels))
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When you run the program, the output will be:
The hash is: -695778075465126279
How hash() works for custom objects?
As stated above, hash() method internally calls
__hash__()
method. So, any objects can override the __hash__() for custom hash values.But for correct hash implementation, __hash__() should always return an integer. And, both __eq__() and __hash__() methods have to be implemented.
Below are the cases for correct __hash__() override.
__eq__() | __hash__() | Description |
---|---|---|
Defined (by default) | Defined (by default) | If left as is, all objects compare unequal (except themselves) |
(If mutable) Defined | Should not be defined | Implementation of hashable collection requires key's hash value be immutable |
Not defined | Should not be defined | If __eq__() isn't defined, __hash__() should not be defined. |
Defined | Not defined | Class instances will not be usable as hashable collection. __hash__() implicity set to None Raises TypeError exception if tried to retrieve the hash. |
Defined | Retain from Parent | __hash__ = <ParentClass>.__hash__ |
Defined | Doesn't want to hash | __hash__ = None Raises TypeError exception if tried to retrieve the hash. |
Example 3: hash() for Custom Objects by overriding __hash__()
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class Person:
def __init__(self, age, name):
self.age = age
self.name = name
def __eq__(self, other):
return self.age == other.age and self.name == other.name
def __hash__(self):
print('The hash is:')
return hash((self.age, self.name))
person = Person(23, 'Adam')
print(hash(person))
------------------------------------------------------------------------------------------------------------
When you run the program, the output will be:
The hash is:
3785419240612877014Note: You don't have to implement the __eq__() method for the hash as it is created by default for all objects.