concept _ _ init _ _ in category python

This is an excerpt from Manning's book Python Workout: 50 ten-minute exercises. Login to get full access to this book.

Table 9.1 What you need to know (view table figure)

Concept	What is it?	Example	To learn more
class	Keyword for creating Python classes	class Foo	http://mng.bz/1zAV
__init__	Method invoked automatically when a new instance is created	def __init__(self):	http://mng.bz/PAa9
__repr__	Method that returns a string containing an object’s printed representation	def __repr__(self):	http://mng.bz/Jyv0
super built-in	Returns a proxy object on which methods can be invoked; typically used to invoke a method on a parent class	super().__init__()	http://mng.bz/wB0q
dataclasses .dataclass	A decorator that simplifies the definition of classes	@dataclass	http://mng.bz/qMew

It creates a new instance of Person and holds onto it as a local variable. But then __new__ calls __init__. It passes the newly created object as the first argument to __init__, then it passes all additional arguments using *args and **kwargs, as shown in figure 9.4.

__Figure 9.4 new__ then calls __init__.

Now __init__ adds one or more attributes to the new object, as shown in figure 9.5, which it knows as self, a local variable.

Figure 9.5 __init__ adds attributes to the object.

class LoudIterator():
    def __init__(self, data):
        print('\tNow in __init__')
        self.data = data                        #1
        self.index = 0                          #2
 
    def __iter__(self):
        print('\tNow in __iter__')
        return self                             #3
 
    def __next__(self):
        print('\tNow in __next__')
        if self.index >= len(self.data):        #4
            print(
                f'\tself.index ({self.index}) is too big; exiting')
            raise StopIteration
 
        value = self.data[self.index]           #5
        self.index += 1                         #6
        print('\tGot value {value}, incremented index to {self.index}')
        return value
 
 
for one_item in LoudIterator('abc'):
    print(one_item)

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This is an excerpt from Manning's book Get Programming: Learn to code with Python. Login to get full access to this book.

31.2.1. Initializing an object with __init__

To initialize your object, you have to implement a special operation, the __init__ operation (notice the double underscores before and after the word init):

class Circle(object):
    def __init__(self):
       # code here

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The __init__ definition looks like a function, except it’s defined inside a class. Any function defined inside a class is named a method.