input: Write a function to improve the provided function by using Python built-in functions. The original function takes in an array of numbers and returns the sum of all the numbers by iterating through the array and adding each number to a total. The improved function should achieve the same result using 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([0, -1, 1]) == 0
  assert sum_array([]) == 0
  assert sum_array([5]) == 5
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)