input: Write a function that improves the `sum_array` function by using Python built-in functions. The improved function should accept an array of numbers and return the sum of all the numbers in the array. If the input array is empty, the function should return 0.
  
  def sum_array(array):
      '''A function that takes in an array of numbers and returns the sum of all the numbers'''
      return sum(array)
  
  assert sum_array([1, 2, 3, 4, 5])==15
  assert sum_array([0, -1, 1])==0
  assert sum_array([])==0
  assert sum_array([-1, -2, -3, -4, -5])==-15
  assert sum_array([10, 20, 30])==60
output: def sum_array(array):
      return sum(array)