python using __init__ vs just defining variables in class - any difference?
oop, python
Solution
When you create variables in the Class, then they are Class variables (They are common to all the objects of the class), when you initialize the variables in `__init__` with `self.variable_name = value` then they are created per instance and called instance variables.
For example,
class TestClass(object):
variable = 1
var_1, var_2 = TestClass(), TestClass()
print var_1.variable is var_2.variable
# True
print TestClass.variable is var_1.variable
# True
Since variable is a class variable, the `is` operator evaluates to `True`. But, in case of instance variables,
class TestClass(object):
def __init__(self, value):
self.variable = value
var_1, var_2 = TestClass(1), TestClass(2)
print var_1.variable is var_2.variable
# False
print TestClass.variable is var_1.variable
# AttributeError: type object 'TestClass' has no attribute 'variable'
And you cannot access an instance variable, with just the class name.
Problem
I'm new to Python - and just trying to better understand the logic behind certain things. Why would I write this way (default variables are in `__init__`): ``` class Dawg: def __init__(self): self.previousWord = "" self.root = DawgNode() self.uncheckedNodes = [] self.minimizedNodes = {} def insert( self, word ): #... def finish( self ): #... ``` Instead of this: ``` class Dawg: previousWord = "" root = DawgNode() uncheckedNodes = [] minimizedNodes = {} def insert( self, word ): #... def finish( self ): #... ``` I mean - why do I need to use `__init__` -> if I can just as easily add default variables to a class directly?