# Fractional ideals for $\mathbb{Z}$

Why isn't it possible to construct fractional ideals for the integers $\mathbb{Z}$?

```
sage: ZZ.fractional_ideal(3/5)
AttributeError: 'sage.rings.integer_ring.IntegerRing_class' object has no attribute 'fractional_ideal'
sage: II = ZZ.ideal(5)
sage: II^(-1)
TypeError: bad operand type for unary ~: 'Ideal_pid'
```

But absurdly this works:

```
sage: JJ = NumberField(x-7,"a").ring_of_integers().fractional_ideal(3/5)
sage: JJ^(-1)
Fractional ideal (5/3)
```

What should I do? Use this crude workaround?

Related: http://math.stackexchange.com/questio...

According to http://math.stackexchange.com/questio... and https://groups.google.com/d/topic/sag... this workaround is the way to go.