Special __init__() method

Question

In python we can access class and object directly without using/initialize __init__ special method? Is __init__ same also a constructor?

• Barmar: Yes, it's similar to constructors in other languages.
• mkrieger1: (1) Yes, (2) no. Was there a particular problem with something you tried?
• Barmar: It's optional if you don't need to initialize anything when the new instance is created.
• blazej: This topic has been already picked up so many times on StackOverflow. I think this is the most popular: stackoverflow.com/questions/8609153/…

Answer 1

In fact it is not a constructor. As it's name says, it's "initializer". In python __new__ constructs the new instances and then __init__ initializes it.

If you don't want to do initialization, you don't need to implement it.

• kaya3: How exactly does this differ from constructors in, say, Java, which also initialise newly-created objects? Wikipedia's article on constructors says, for example, "They have the task of initializing the object's data members"; do you have a source which says that is not the job of a constructor?
• S.B: @kaya3 unfortunately I don't know about what's going on in Java. In python __new__ has the duty of creating new instance object. Of course you can interpret that and do your "initialization" there if you want and skip the __init__ method totally. But mostly we do initialization in __init__. As a proof, Try to implement __new__ method and return something else like 10. Then the __init__ won't get called at all. __init__ gets called exactly after the __new__ method created the object (if the conditions are present).
• kaya3: In Java, the new keyword creates the object, and a constructor initialises the new object, just like Python's __init__. I've heard it said that, for this reason, Java's constructors are not really constructors, they are initialisers - but this doesn't seem to agree with the way the word "constructor" is used by authoritative sources, so I'm wondering if you know of a textbook or other source which does distinguish between constructors vs. initialisers as general, language-independent terms (as opposed to in a specific language like C#).
• kaya3: Compare for example, Javascript's so-called "arrays" which are really lists, and PHP's so-called "arrays" which are really maps or associative arrays. Those languages use the word "array" in a non-standard way compared to how authoritative sources define the word "array", so it's entirely possible there's a standard by which Java's "constructors" are not truly constructors; I just don't know of one.
• S.B: @kaya3 docs.python.org/3/reference/datamodel.html#object.__new__ It uses the word constructor for __new__ and initializer for __init__