User-Defined Objects
By default, user-defined objects in Python are not interned. However, you can implement your own interning mechanism by overriding the __new__ method of the class. By doing so you can control object instantiation and reuse existing instances based on specific criteria.
Example :
In this code, you create two instances of MyClass with different values: 20 and 50. Since the instances have different values, they are considered different objects, and therefore a is b returns False.
However, if you were to create another instance of MyClass with the value 20, it would return the existing instance created earlier, and a is b would then return True.
Python3
class MyClass: _instances = {} def __new__(cls, value): if value in cls._instances: return cls._instances[value] else: instance = super().__new__(cls) cls._instances[value] = instance return instance def __init__(self, value): self.value = valuea = MyClass(20)b = MyClass(50)print(a is b) |
Output :
1764283301312
1764283301216
False
Object Interning In Python
Object interning is a technique used in Python to optimize memory usage and improve performance by reusing immutable objects instead of creating new instances. It is particularly useful for strings, integers and user-defined objects. By interning objects, Python can store only one copy of each distinct object in memory reducing memory consumption and speeding up operations that rely on object comparisons.
Syntax :
import sys
interned_string = sys.intern(“string_to_intern”)
- We import the
sysmodule usingimporta statement. - The
sys.intern()the function is called with a string argument that you want to the intern. - The interned string is assigned to a variable, typically with a different name to the indicate that it is interned.
Example :
In this code, you have two pairs of string variables: string1 and string2, and interned_string1 and interned_string2.
Python3
import sysstring1 = "Hello"string2 = "Hello"interned_string1 = sys.intern(string1)interned_string2 = sys.intern(string2)print(string1 is string2) print(interned_string1 is interned_string2) |
Output :
True
True