What Is The Difference Between A Constructer And Initializer In Python?

Possible Duplicate: Python (and Python C API): new versus init I'm at college just now and the lecturer was using the terms constructors and initializers interchangeably. I'm pr

Solution 1:

In most OO languages, they are the same step, so he's not wrong for things like java, c++, etc. In python they are done in two steps: __new__ is the constructor; __init__ is the initializer.

Here is another answer that goes into more detail about the differences between them.

Solution 2:

In almost all usual cases, Python does not have constructors in the same sense used by other OO languages because manually managing memory is generally discouraged. Instead, what you should usually do is define an __init__ method on the class. This method is called to initialize the new instance object automatically, first thing after it is constructed. Thus, it is not really a constructor, and talking about it as a constructor might confuse some people.

Of course some people want to call it a constructor because it is used a little bit like a constructor - fundamentally you can call it whatever you want as long as everyone understands what you are actually referring to. But in general, to be explicit and make yourself understood, call it an init method or something other than a constructor. Fundamentally, different languages just come with somewhat different terminology and speaking very clearly will always require adjustment to your subject matter and audience.

In Python it is possible to manage instance creation and destruction at a finer granularity, though you won't want to unless you know what you're doing. This is done by defining __new__ and __del__ methods to hook object instantiation and del statements. Whether these qualify as constructors and destructors precisely is a little more debatable (Python docs call the del method a destructor, but tend to be vaguer on what constitutes a constructor, e.g. including many functions which return object instances). I'd still encourage you to use the specific terminology for the language at hand, and in comparative discussions to define your terms up front. As always, your choice of terms while speaking involves tradeoffs between the audience being able to easily follow you and the audience potentially being led into confusion: if you are talking about memory management probably be as specific as possible, but if you are talking loosely then just use some word your audience understands and be ready to clarify.

Your instructor is being unclear at worst, I'm not aware of any one canonical definition of these terms but they might cause confusion for people who have learned very specific definitions from other languages.

Solution 3:

http://docs.python.org/reference/datamodel.html#basic-customization

__new__ - constructor.

__init__ - initializer.