My 5th kata, and 1st in a planned series of rock climbing themed katas.
In rock climbing ([bouldering](https://en.wikipedia.org/wiki/Bouldering) specifically), the V/Vermin (USA) climbing grades start at `'VB'` (the easiest grade), and then go `'V0'`, `'V0+'`, `'V1'`, `'V2'`, `'V3'`, `'V4'`, `'V5'` etc. up to `'V17'` (the hardest grade). You will be given a `list` (`lst`) of climbing grades and you have to write a function (`sort_grades`) to `return` a `list` of the grades sorted easiest to hardest.
If the input is an empty `list`, `return` an empty `list`; otherwise the input will always be a valid `list` of one or more grades.
Please do vote, rank, and provide any feedback on the kata.
def sort_grades(gs):
  return sorted(gs, key=grade)

def grade(v):
  if v == 'VB':  return -2
  if v == 'V0':  return -1
  if v == 'V0+': return  0
  return int(v[1:])
def sort_grades(gs):
  return sorted(gs, key=grade)

def grade(v):
  if v == 'VB':  return -2
  if v == 'V0':  return -1
  if v == 'V0+': return  0
  return int(v[1:])