input: Write a function to improve the given function `sum_array(array)` by using Python built-in functions. The `sum_array(array)` function takes in an array of numbers and returns the sum of all the numbers.
  assert sum_array([1, 2, 3, 4, 5])==15
  assert sum_array([0, 0, 0, 0])==0
  assert sum_array([-1, -2, -3, -4, -5])==-15
  assert sum_array([])==0
  assert sum_array([10])==10
output: def sum_array(array):
      return sum(array)