Python’s magic methods __new__
and __init__
play complementary roles in the lifecycle of an object:
π __new__
is a static method, primarily concerned with creating and returning a new instance of a class; it acts before the object is fully instantiated in memory.
π Following this, __init__
functions as an instance method, tasked with configuring the specific attributes of the newly minted object, thus defining its initial state.
This orchestrated sequence ensures that the structural foundation established by __new__
precedes the customization of the object’s properties through __init__
.
This design provides a clear and methodical approach to object creation and initialization in Python.
Minimal Example
Here’s a simple example that demonstrates the difference between __new__
and __init__
in Python:
class MyClass: def __new__(cls): print("Creating instance") return super(MyClass, cls).__new__(cls) def __init__(self): print("Initializing instance") # Creating an object of MyClass obj = MyClass()
In this example:
- When
MyClass()
is invoked,__new__
is called first. It is responsible for creating and returning a new instance of the class. Here, it prints “Creating instance” and usessuper()
to call the__new__
method of the superclass to allocate the memory for the new object. - Once the new instance is created and returned by
__new__
,__init__
is called to initialize the new object. In this case, it prints “Initializing instance”.
This output illustrates the order and roles of __new__
and __init__
in Python’s object creation process.
FAQ: Understanding __new__
and __init__
in Python
1. What is the purpose of __new__
in Python?
__new__
is a static method responsible for creating a new instance of a class. It is the first step in the instance creation process, handling memory allocation before any attributes are initialized.
2. How does __init__
differ from __new__
?
While __new__
creates the instance, __init__
is tasked with initializing the newly created object’s attributes. It sets up the initial state of the object after __new__
has already created it.
3. When would you need to override __new__
instead of __init__
?
Overriding __new__
is less common but is necessary when you need to control the creation of a new instance, such as enforcing certain patterns (like singletons), modifying immutable types, or extending immutable types like tuples and strings.
4. Can __init__
return a value?
No, __init__
should not return anything except None
. It is designed purely for initialization and not for creating new instances, which is the role of __new__
.
5. What happens if __new__
does not return an instance of the class?
If __new__
returns something that isn’t an instance of the class in which it’s defined, then __init__
will not be called. This can be used intentionally to control the type of objects your class creates or returns.
6. Is it mandatory to call the base classβs __new__
when overriding it?
Yes, generally you should call the base classβs __new__
using super()
to ensure that the object gets properly created before you attempt to initialize it in __init__
.
7. Can __init__
be called multiple times on the same instance?
Yes, __init__
can technically be called multiple times for the same instance, allowing reinitialization of the object. However, __new__
is typically called only once per object creation.
8. Are __new__
and __init__
only relevant to classes defined in Python code?
__new__
and __init__
are relevant for any class, including those from Pythonβs standard library or third-party libraries that follow the object-oriented paradigm.
π Understanding the Differences Between self and init Methods in Python Classes