# complete expansion of polynomial substitution

In the following code, I have substituted a polynomial in other polynomial and the result even after using the command ".expand" shows no complete expansion,Is there any other way to get complete expansion of polynomial substitution?

```
g1=1+ (s^2) ;
g2=g1.subs(s= 1/(z-1) ) ;
g2.expand()
```

Result: 1+ 1/((z-1)^2) is shown, but not expansion (z^2-z+2)/z^2-z+1.