input: Write a function to improve the following code by using Python built-in functions:
  
  ### Input:
  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
  
  ### 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)
  
  assert sum_array([1, 2, 3, 4])==10
  assert sum_array([5, 10, 15])==30
  assert sum_array([0, 0, 0])==0
  assert sum_array([-1, 1, -1, 1])==0
  assert sum_array([])==0
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)