When you break lines like this, put the comma on the previous line, like

```py
return cds_cancel_primitive(a, Poly(b1, DE.t), Poly(b2, DE.t), Poly(c1, DE.t),
    Poly(c2, DE.t), DE, n)
```

Also note that you don't need the `\` because you are breaking the line in the middle of parentheses.