input: Write a function to improve the existing function by using Python built-in functions. The given function is:
  
  def sum_array(array):
      '''A function that takes in an array of numbers and returns the sum of all the numbers'''
      total = 0
      for num in array:
          total = total + num
      return total
  
  assert sum_array([1, 2, 3, 4, 5])==15
  assert sum_array([-1, -2, -3, -4, -5])==-15
  assert sum_array([])==0
  assert sum_array([10, 20, 30])==60
  assert sum_array([0, 0, 0])==0
  
  The improved function should be:
  
  def sum_array(array):
      '''A function that takes in an array of numbers and returns the sum of all the numbers'''
      return sum(array)
output: def sum_array(array):
      '''A function that takes in an array of numbers and returns the sum of all the numbers'''
      return sum(array)