`id` is invalid 

```
119: C0103: (invalid-name), LoncapaProblem.__init__: Invalid name "id" for type argument (should match [a-z_][a-z0-9_]{2,30}$)
119: C0103: (invalid-name), LoncapaProblem.__init__: Invalid name "id" for type variable (should match [a-z_][a-z0-9_]{2,30}$)
119: W0622: (redefined-builtin), LoncapaProblem.__init__: Redefining built-in 'id'
```