'int' object has no attribute 'digits'

edit

The issue is that the range function outputs numbers of the type Python int rather than Sage Integer, and digits is only defined for the latter. You could use Sage's srange function instead:

for i in range(2):
    print(type(i))

will produce

<class 'int'>
<class 'int'>

whereas

for i in srange(2):
    print(type(i))

will give

<class 'sage.rings.integer.Integer'>
<class 'sage.rings.integer.Integer'>

This should work:

for j in range(3,4):
    print(Integer(j).digits(3))