How to write a code to get this kind of output in IDLE

[kavindu]

In IDLE I imported sympy.matrices module

for an example
I entered the following

>>> from sympy.matrices import Matrix
>>> a=Matrix([[1,2,3],[4,5,6],[7,8,9]])
>>> a
Matrix([
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])

and also I imported a custom library created by me.
this is a part of my module

class dog:
    def __init__(self,name,age,gender):
        self.name=name
        self.age=age
        self.gender=gender

In IDLE I entered following in the same as the previous

>>> from my_modules.dog import dog
>>> b=dog("sam",5,"male")
>>> b
<my_modules.dog.dog object at 0x00460950>

the problem is I entered codes in the same way. But the outputs are in the different forms

in first example it gave the following output instead of giving an output
just like <sympy.matrices.Matrix object at 0x00512950>

Output:
Matrix([
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])

I need to know how to code my custom module to return an output just like

>>>b
Dog('sam','5years','male')

instead of <my_modules.dog.dog object at 0x00460950>

can someone help Me please