Technically the __new__ method takes a class and generates an instance of that class. __init__ is used to then initialize the properties of the instance that was created by __new__. So __new__ is the constructor: Its job is to build a new instance object using the class as a template. I think it is very rare to override __new__ because its default behaviour, which is to create an empty instance of the particular class, is usually what we want.
In everyday Python programming, we just override the __init__ method to assign values to the object that was already created earlier by the default __new__ behaviour. __init__ is not the constructor, since it receives a pre-created instance object as a parameter - usually we call this parameter self. Instead, it's an initializer - it initializes an instance object.
As an example, and there are probably more ways to do this, you could override __new__ to limit the number of instances of an object that can be created, or to obtain them from a pool, that sort of idea. So there are probably use-cases for overriding __new__ but I doubt that you'd need to worry about it for everyday usage.
Update: I looked into the nomenclature, and it does not seem to me that Python has the concept of "constructor" used in the documentation in the same way that it's used for languages like Java or C++. Instead the docs mention that the call used to create an object, like say Foo(), is a constructor expression:
This constructor expression calls __new__ and then __init__ internally. I guess neither of the latter would officially be called a constructor. I think it's okay to call __init__ the constructor informally though, since it does pretty much the same kind of thing that constructors in languages like Java, C#, C++ do.
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Technically the
__new__method takes a class and generates an instance of that class.__init__is used to then initialize the properties of the instance that was created by__new__. So__new__is the constructor: Its job is to build a new instance object using the class as a template. I think it is very rare to override__new__because its default behaviour, which is to create an empty instance of the particular class, is usually what we want.In everyday Python programming, we just override the
__init__method to assign values to the object that was already created earlier by the default__new__behaviour.__init__is not the constructor, since it receives a pre-created instance object as a parameter - usually we call this parameterself. Instead, it's an initializer - it initializes an instance object.As an example, and there are probably more ways to do this, you could override
__new__to limit the number of instances of an object that can be created, or to obtain them from a pool, that sort of idea. So there are probably use-cases for overriding__new__but I doubt that you'd need to worry about it for everyday usage.Update: I looked into the nomenclature, and it does not seem to me that Python has the concept of "constructor" used in the documentation in the same way that it's used for languages like Java or C++. Instead the docs mention that the call used to create an object, like say
Foo(), is a constructor expression:docs.python.org/3/reference/datamo...
This constructor expression calls
__new__and then__init__internally. I guess neither of the latter would officially be called a constructor. I think it's okay to call__init__the constructor informally though, since it does pretty much the same kind of thing that constructors in languages like Java, C#, C++ do.