Sorts a list. Takes one or two arguments, the first being a list and the second being a function or None. The function should take the keyword argument key. If None is passed as the second argument, the function will sort by identity.

a = sort([4, 1, 7, 10, 5]) # b = [1, 4, 5, 7, 10]
b = sort([4, 1, 7, 10, 5], None) # a = [1, 4, 5, 7, 10]

def key_fn(key=''):
  return key['name']
c = sort([
  {'name': 'John'},
  {'name': 'Bob'},
  {'name': 'Charles'},
], key_fn) # c = [{'name': 'Bob'}, {'name': 'Charles'}, {'name': 'John'}]