Python error (1): takes no arguments

I'm learning python Of class when , Try running the following code ：

# Create a class
class Dog():
""" A simple attempt to simulate a puppy """
def _init_(self,name,age):
""" Initialization property namez and age"""
self.name = name
self.age = age
def sit(self):
""" Simulate a puppy crouching when ordered """
print(self.name.title()+" is now sitting.")
def roll_over(self):
""" Simulate a puppy rolling when ordered """
print(self.name.title()+" rolled over!")

appear Report errors ：

Finally found The mistake is ：

among __init__() Before and after the method should be Two “_” !

summary ：

In class , Method __init__( ) It's a special method , It supports Initialization of classes with parameters , Or for Declare the properties of this class , In the name of the method , There are... At the beginning and at the end Two underscores ！