class Matrix(list):
    def __init__(self):
        super(Matrix, self).__init__()
        self.size = 5
    def init_field(self):
        line = [0] * self.size
        self.extend([line[:] for _ in range(self.size)])

[[0 0 0 0 0]
 [0 0 0 0 0]
 [0 0 0 0 0]
 [0 0 0 0 0]
 [0 0 0 0 0]]

    def __str__(self):
        return '\n'.join(str(row) for row in self)

import numpy as np
from UserList import UserList as ul
class Matrix(ul):
    def __init__(self):
        super(Matrix, self).__init__()
        self.size = 5
        self.init_field()
    def init_field(self):
        line = [0] * self.size
        self.extend([line[:] for _ in range(self.size)])
    def __str__(self):
        return str(np.array(self))
>>> obj=Matrix()
>>> print obj
[[0 0 0 0 0]
 [0 0 0 0 0]
 [0 0 0 0 0]
 [0 0 0 0 0]
 [0 0 0 0 0]]

>>> def func(m):
...     out = '['
...     first = True
...     for i in m:
...         if first:
...             first = False
...         else:
...             out += '\n '
...         out += str(i).replace(',', '')
...     out += ']'
...     return out
... 
>>> class A:
...     
...     lst = [[1, 2, 3], [4, 5, 6]]
...     
...     __str__ = lambda self: func(self.lst)
... 
>>> a = A()
>>> print(a)
[[1 2 3]
 [4 5 6]]
>>>