Convert Python codes to Nim codes

[PMunch]

Ah, my bad. Nim doesn't have a slice operator like that AFAIK, so you'll have 
to use something like collect to get that working. As for your new error that 
is again because you're using `len` and not `high`. Nims `..` slice is 
inclusive, and iterating to the length of a collection will therefore try to 
step one step too far. If you use `high` you're looping to the highest 
available index, or you could use `..<` which loops to N-1.