Aivar, I have to admit that my knowledge of this is limited, but as I understand it, the attribute is "bar" in the "foo.bar" expression.

I can get beginning of the assignment by 
>>> ast.parse('foo.bar').body[0].value.value.col_offset
0

But how can I get position of the 'bar'? My guess is this:
>>> ast.parse('foo.bar').body[0].value.col_offset
but it still returns 0.

Why this two col_offsets returns the same value? How can I get the position of 'bar' in 'foo.bar'?