Python “自我”约定 __init__ 与方法

Question

class MyClass(object):
   def __init__(self):
       self.var = "hi"

   def some_method(self):
       print self.var

#for the example below
myClass= MyClass()

So I understand that the following statements are equivelent.

myClass.some_method()
MyClass.some_method(myClass)

It takes object and passes it as the first argument self to some_method .

But when I do:

myClass= MyClass()

How does this flow work?

I am assuming its slightly different, and some magic happens behind the scenes (someone has some memory to allocate).

How does that translate to __init__(self) ? What is passed to __init__ MyClass ?

Answer 1

myClass= MyClass() calls MyClass.__new__ method to create an instance of MyClass . After that MyClass.__init__ is called with this instance as first argument.

See the doc object.__new__ :

object. __new__ (cls[, ...])

Called to create a new instance of class cls.

object. __init__ (self[, ...])

Called when the instance is created.

Answer 2

__init__() method is called immediately after an instance of the class is created.

Dive into Python - Initializing and Coding Classes

Answer 3

MyClass() creates a brand new object, which is passed to __init__(self) as the parameter self . You can then set up whatever fields you want on self , and then MyClass() returns it.